Javastudypoint

How to install Go on Windows, Linux and MacOS

2023-08-28T23:11:00.001+05:30

This post will show how to install Go on Windows, Linux, and MacOS. Before installing Go, It's essential to know what GoLang is. Go is an open-source, compiled, high-level, and statically typed programming language. It is also known as GoLang. It was designed at Google in 2007 by Robert Griesemer, Rob Pike, and Ken Thompson. It was developed to improve programming productivity in the era of multicore, networked machines, and large codebases. Go is widely used in production at Google and in many other organizations and open-source projects. For more details about GoLang refer to this article Introduction to Go Programming Language

Let's discuss how to install Go on Windows, Linux, and macOS

How to Install Go on Windows:

To install Go on a Windows system, follow these steps:

Go to the official GoLang website's download page: https://golang.org/dl/. Download the Windows installer that matches your system architecture (either 32-bit or 64-bit).
Once the installer is downloaded, double-click on it to run it. The installer will guide you through the installation process.

Click on the next and You will be asked to choose the installation location. The default location is fine but you can choose according to your preference.

After making your selections, click on next and then click the "Install" button to start the installation.

Once the installation is complete, you can verify whether Go has been installed successfully or not. Open a command prompt (CMD) or PowerShell window and type: "go version". If the Go is installed successfully, You will get a displayed Go version on the CMD screen.

How to install Go on Linux

To install Go on a Linux system, follow these steps:

Go to the official GoLang website's download page: https://golang.org/dl/. Download the tar file.

Once the tar file is downloaded, remove any previous Go installation by deleting the /usr/local/go folder (if it exists), then extract the archive you just downloaded into /usr/local


$ rm -rf /usr/local/go && tar -C /usr/local -xzf go1.21.0.linux-amd64.tar.gz

Add /usr/local/go/bin to the PATH environment variable. You can do this by adding the following line to your $HOME/.profile or /etc/profile


export PATH=$PATH:/usr/local/go/bin

Save the profile file and then run source .profile to apply the changes in the system.

Now you can check whether Go is installed successfully by using the "go version" command. If the Go is installed successfully, You will get a displayed Go version


source .profile

go version
go version go1.21.0 windows/amd64

How to install Go on MacOs

To install Go on a Mac system, follow these steps:

Go to the official Golang website download page https://golang.org/dl/. You will see different options for Golang download for different operating systems. Look at the Mac System version and download it.
Once it is downloaded start the installation process. Follow the on-screen instructions in the installer.
Once the installation is complete, you can check the Go installation using go version command


go version
go version go1.21.0 windows/amd64

What is GoLang? Introduction to Go Programming Language

2023-08-12T21:15:00.000+05:30

Go is an open-source, compiled, high-level, and statically typed programming language. It is also known as GoLang. It was designed at Google in 2007 by Robert Griesemer, Rob Pike, and Ken Thompson. It is developed to improve programming productivity in the era of multicore, networked machines, and large codebases. Go was publicly launched in 2009 and version 1.0 was released in March 2012. Go is widely used in production at Google and in many other organizations and open-source projects.

Why should you learn GoLang?

Go language is one of the fastest-growing, in-demand skills and rising programming languages and it makes sense to learn Go language to develop Software in a quicker time. Let's discuss some use cases to learn to Go Programming Language.

Cloud and Network Services:

GoLang helps enterprises build and scale cloud computing systems. Most of the cloud-native software is written in GoLang. The major cloud providers like GCP (Google Cloud Platform), AWS (Amazon Web Services), and Azure have Go APIs for services, and popular open-source libraries provide support for API tooling (Swagger), transport (protocol buffers, gRPC), monitoring (OpenCensus), Object-Relational Mapping (gORM), and authentication (JWT). The open-source community also provided several frameworks including Go Kit, Go Micro, and Gizmo which can help the developer to build the cloud-based application easily and in a quicker time.

There are two widely used Go tools for cloud computing Docker and Kubernetes. Clod Developers use docker to quickly deploy and scale applications into any environment and developers use Kubernetes to build, deliver, and scale containerized apps quickly.

CLI (Command Line Interfaces):

CLI developers prefer Golang portability, performance, and ease of creation. Developers of CLIs find Go to be ideal for designing their applications. Go compiles very quickly into a single binary, works across platforms with a consistent style, and brings a strong development community. From a single Windows or Mac laptop, developers can build a Go program for every one of the dozens of architectures and operating systems Go supports in a matter of seconds, no complicated build farms are needed. No other compiled language can be built as portably or quickly. Go applications are built into a single self-contained binary making installing Go applications trivial.

When developing CLIs in Golang, two tools are widely used: Cobra & Viper

Cobra is a Golang library for creating powerful modern CLI interfaces. In addition to providing an interface, Cobra simultaneously provides a controller to organize your application code.

Viper is a complete configuration solution for Go applications, designed to work within an app to handle configuration needs and formats. Cobra and Viper are designed to work together. Viper supports nested structures in the configuration, allowing CLI developers to manage the configuration for multiple parts of a large application. Viper also provides all of the tooling needed to easily build twelve-factor apps.

GoLang for Web Development:

Go can be an excellent choice for web development, particularly for applications that prioritize performance, scalability, and concurrent handling of requests. Go is designed to enable developers to rapidly develop scalable and secure web applications. Go have standard libraries that include packages for building web servers, handling HTTP requests, and working with templates. This reduces the need for third-party libraries and simplifies the development process.

Go has excellent support for all of the latest technologies from HTTP/2, to databases like MySQL, MongoDB, and Elasticsearch, to the latest encryption standards including TLS 1.3 that help to develop secure and user-friendly web applications.

Development Operations & Site Reliability Engineering:

Go offers several features and benefits that can greatly assist Development Operations (DevOps) and Site Reliability Engineering (SRE) teams in their day-to-day tasks and responsibilities. Go compiles very quickly into a single binary, Go's single-binary output means that DevOps and SRE teams can package their tools and services as standalone executables, reducing dependencies and easing deployment across various environments.

Go can be used to create custom automation scripts and tools that streamline CI/CD pipelines, automate testing, deployment, and monitoring, and enhance overall workflow efficiency.

How GoLang is different from other programming languages

The most notable difference between GoLang and many other programming languages is its concurrency model. Traditional general-purpose programming languages use threads provided and scheduled by the operating system (or a rather abstract concept of “workers” that are based on OS threads) to allow you to run multiple functions concurrently.

Those threads usually have a stack of a few megabytes in memory meaning that you can’t spawn too many of them, for example, 1000 threads where each consumes 1 MB of memory would require 1 GB of memory already.

Requesting a thread from the operating system isn’t cheap, you better take as many as you need during the initialization phase of your program and reuse them.

Context switches on OS threads aren’t cheap. Most registers and some caches will need to be swapped out.

The limitations associated with OS threads make writing non-blocking concurrent systems unnecessarily difficult. Go has a completely different concurrency model. In Go, you can run functions in separate so-called “goroutines”.

Go’s goroutines have a flexible stack that’s at least 2kb in memory and it grows as needed. This means that you can literally spawn millions of them compared to only thousands of threads.

Goroutines are multiplexed through an OS thread pool in the built-in runtime and can thus achieve 99.9% CPU utilization.

They’re scheduled cooperatively, meaning that they return control to the built-in user-space scheduler when they’re getting blocked (by, for example, a database operation)

Context switches on goroutines are very cheap since fewer registers need to be swapped out.

Creating and suspending goroutines is very cheap because it’s done on the application level and doesn’t require a system-space roundtrip.

Finally, what makes Go unique in a sense, is the combination of compilation to actual binary executables, the concurrency model, the runtime, the garbage collector, and the particular qualities of the language itself.

Limitations of GoLang

One of the most notable limitations of GoLang is the lack of generics, which can make code more repetitive and less abstract.
Golang doesn't have direct support for object-oriented programming. But we can achieve OOP in Go with the help of struct and interfaces.
There is no implicit type conversion in Golang, which can sometimes result in more explicit type casting in code.

Reference: Golang Offical Documentation

What is the difference between final and immutable in Java?

2020-01-28T19:16:00.000+05:30

Final: The Final in Java is a keyword that is applicable for only variables, methods, and class. The Java Final Keyword is used to restrict the user to use variables, methods, and class. The Final keyword is applicable for all the types of variables such as for instance variable, static variable, and local variable. When a variable declared as final and assigned a value, you can't change the value of the variable. The final method can't be overridden by the child class. A class that is declared final cannot be extended.

immutability: Immutability means once we create an object we are not allowed to change the content of that object. If any person trying to change the content if there is a change in the content with those changes a new object will be created. If there are no changes in the content existing object will be reused.

Final vs immutable in Java:

1. Final means that you can't change the object reference to point to another reference or another object, but you can still mutate its state (by using the setter method). Where immutable means that the object's actual value can't be changed, but you can change its reference to another one.

2. The modifier final is applicable for variables not for objects, Whereas immutability applicable for objects not for variables.

3. Final ensures that the address of the object remains the same, Whereas the immutable suggest that we can't change the state of the object once created.

4. By declaring the reference variable as final we are not going to get any immutability nature but we can perform any type of changes in the corresponding objects and we can't reassign reference variable to any new object

Java program to demonstrate the difference between final and immutability:

class Test{
 public static void main(String args[]){
  final StringBuffer sb = new StringBuffer("Java");
  
  //Even though reference variable is final
  //we can perform any changes to corresponding object.
  sb.append("studypoint");
  System.out.println(sb);
  
  //Here, we will get compile time error because
  //we can't reassign reference variable to any new object.
  sb = new StringBuffer("Hello Javastudypoint");
  System.out.println(sb);
 }
}

Output:

Diagrammatically representation of the above program.

Explanation: In the above diagram, we can see that we are creating an object of StringBuffer class by making the reference variable as final.

1. By declaring a reference variable final, it does not mean that the object is immutable in nature.
2. In the second line, we are performing append() operation on the created object and it is successfully changed.
3. If the object is immutable, the above operation can't be done.
4. But it is executed successfully as we declare reference variable as final, which means we can't reassign anything to that reference variable again.
5. Therefore when we try to create a new object of StringBuffer class then it won't be created and we will get a compile-time error.

Reference: final vs immutability in Java.

You may also like these posts:

1. How to compare two strings lexicographically in Java?
2. How to remove leading and trailing whitespaces from a string?
3. How to convert a string into a char array?
4. Types of operators in Java with example.
5. Java OOPs Concepts with Example.
6. How to replace a string in Java?

How we can create our own immutable class in java?

2020-01-26T00:07:00.000+05:30

In the previous tutorial, we have learned about String class, we explore its constructors and important methods. In this tutorial, we will learn how to create an immutable class in java. First, before creating our own immutable class, we can recall you about what is immutability.

Immutable class means once we create an object we are not allowed to change the content of that object if any person trying to change the content if there is a change in the content with those changes a new object will be created. If there is no change in the content existing object will be reused. Now let's discuss how to create an immutable class in Java. The following rules define a simple strategy for creating an immutable class.

1. The class must be declared as final so that it can't be extended.
2. Make all the fields final and private.
3. Don't provide "setter" methods — methods that modify fields or objects referred to by fields.
4. Use getter method for all the variables in it.
5. Initialize all the fields via using a parameterized constructor.

Example to create an immutable class:


public final class Test{
	//private and final data member.
	private final int i;
	//parameterized constructor.
	Test(int i){
		this.i = i;
	}
	
	/*modify method with return type test.
	because of this modify method test 
	class becomes immutable. */
	public Test modify(int i){
		/*check current objet i value is equal to
		your provided value(passing argument in constructor). 
		if both are same no change in the content 
		therefore we return current object only. */
		if(this.i == i){
			return this;
		}
		/*if there is change in the content, create 
		a new object with updated i value and return
		that object. */
		else{
			return new Test(i);
		}
	}
	public static void main(String args[]){
		Test t1 = new Test(10);
		Test t2 = t1.modify(100);
		Test t3 = t1.modify(10);
		
		System.out.println(t1 == t2); //false
		System.out.println(t1 == t3); //true;
	}
}

You may also like these posts:

1. How to remove leading and trailing whitespaces from a string?
2. How to compare two strings lexicographically in java?
3. How to find substring in java?
4. How to replace a string in java?
5. How to convert a string into a char array?

How to remove leading and trailing whitespaces from String in Java?

2020-01-09T14:21:00.000+05:30

In the last tutorial, we have learned about string class methods. In this tutorial, we will learn how to remove leading and trailing whitespaces from String. Java String trim() method is used to remove leading and trailing whitespaces from String. In this tutorial, we will learn the trim() method with a small case study. So that, you can understand Java String trim() method with much clarity. Here, we will discuss first what is the need for that method. We will explain its need with an example.

Java String trim() Method

Java String trim() method is used to remove whitespaces either from the beginning and the end of a string. It returns a copy of the string, with leading and trailing whitespace omitted. Let's understand with an example.


import java.util.Scanner;
class TrimExample{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		System.out.println("Enter Country Name: ");
		String country = sc.nextLine();
		
		if(country.equals("india")){
			System.out.println("Capital of india is delhi");
		}
		else if(country.equals("australia")){
			System.out.println("Capital of australia is canberra");
		}
		else if(country.equals("england")){
			System.out.println("Capital of england is london");
		}
		else{
			System.out.println("Please enter a valid country name.");
		}
	}
}

Here, I wrote a simple program where the user entered a country name and corresponding to the entered country name user will see a message where the country capital is printed. Let's run this program. The code compiled and run fine there is no problem at all.

But there are two biggest problems in this code from the programmer point of view.

1. In this program, the end-user is responsible to enter the country name. The end-user entered the country name either lower case or upper case or mixture. But our program always considered lower case only. If the end-user entered country name only in lower case then only our program works. By mistake, if the end-user entered the country name in the upper case letter then our program will not woks. Let's see the example.

There are two solutions to the above problem. First, We can replace equals() method with equalIgnoreCase(). But if in your program there are 1000 lines or 10000 lines then you need to replace equals() method with an equalIgnoreCase() method with 1000 or 10000 times, which is not a good practice.

The second solution is, as we know our program accepts only lower case letters. So, what we will do is, If the end-user entered the country name we will convert into a lower case letter. Then our problem will be solved. So the second solution is very easy because we need to write only one line. See the example below.


import java.util.Scanner;
class TrimExample{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		System.out.println("Enter Country Name: ");
		String country = sc.nextLine().toLowerCase();
		
		if(country.equals("india")){
			System.out.println("Capital of india is delhi");
		}
		else if(country.equals("australia")){
			System.out.println("Capital of australia is canberra");
		}
		else if(country.equals("england")){
			System.out.println("Capital of england is london");
		}
		else{
			System.out.println("Please enter a valid country name.");
		}
	}
}

Output:


Enter Country Name: INdia
Capital of india is delhi
Enter Country Name: ENGLand
Capital of england is london
Enter Country Name: AUSTRALIA
Capital of australia is canberra

2. But still, there is one more problem with this code. As we know, the end-user is responsible to enter the country name. If the end-user entered the country name with some spaces at the starting or ending then our program check is there some spaces followed by a country name is available or not. In our code, this case is not available, then our code will not works and show a message to the end-user please enter a valid country name. Let's see the example.

To resolve this problem, What we can do, before comparing the country name if any spaces entered by the end-user either at the beginning or at the end, If we remove those spaces then our problem will be solved. We can remove spaces either at the beginning or end of the string by using the trim() method.

Java String trim() Method Example


import java.util.Scanner;
class TrimExample{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter Country Name: ");
		String country = sc.nextLine().toLowerCase().trim();
		
		if(country.equals("india")){
			System.out.println("Capital of india is delhi");
		}
		else if(country.equals("australia")){
			System.out.println("Capital of australia is canberra");
		}
		else if(country.equals("england")){
			System.out.println("Capital of england is london");
		}
		else{
			System.out.println("Please enter a valid country name.");
		}
	}
}

Output:


Enter Country Name:   INdia
Capital of india is delhi
Enter Country Name:    ENGLand
Capital of england is london
Enter Country Name:     AUSTRALIA
Capital of australia is canberra

How to Compare two Strings lexicographically in Java?

2020-01-08T19:30:00.000+05:30

The Java String Class provides many ways to compare the content of the two Strings. One way to compare the content of the two strings by using the equals() method. We have learned the equals() method in our last tutorial. In this tutorial, we will learn how to compare two strings lexicographically in Java.

Java String compareTo() Method

Java String compareTo() method is used to compare the two strings lexicographically in Java. The comparison is based on the Unicode value of each character in the string. The String compareTo() method returns the positive number, negative number or 0.

If the first string is greater than the second string lexicographically, then it returns a positive number. If the first string is smaller than the second string lexicographically, then it returns a negative number. If both the strings are equal lexicographically, then it returns 0.

Java program to compare two strings lexicographically

class Lexicographically{
	public static void main(String args[]){
		String str1 = "Hello";
		String str2 = "Hi";
		String str3 = "Ram";
		String str4 = "Javastudypoint";
		String str5 = "Tutorial";
		String str6 = "Tutorial";
		
		//-4 because "e" is 4 times less than "i".
		System.out.println(str1.compareTo(str2));
		
		//2 because "T" is 2 times greater than "R".
		System.out.println(str5.compareTo(str3));
		
		//-2 because "H" is 2 times less than "J".
		System.out.println(str1.compareTo(str4));
		
		//-12 because "H" is 12 times less than "T".
		System.out.println(str1.compareTo(str5));
		
		//0 because both the strings are equal.
		System.out.println(str5.compareTo(str6));
	}
}

Output:


-4
2
-2
-12
0

How to Convert a String to char array in Java?

2020-01-08T14:38:00.000+05:30

In the last tutorial, we have learned how to convert a string to uppercase in Java. We have learned all the two variants of toUpperCase in Java. In this tutorial, we will learn how to convert a string to a char array in Java. We can convert a string to char array by using the toCharArray() method of Java String class. It returns a newly allocated character array whose length is the length of this string.

Syntax: The syntax of the Java String toCharArray() method is given below:


puyblic char[] toCharArray

It converts this string to a new character array.

Java program to convert a string to char array.


class toCharArray{
	public static void main(String args[]){
		String str = "Java";
		
		//converting string to char array.
		char ch[] = str.toCharArray();
		
		//printing the char array.
		for(int i=0; i<ch.length; i++){
			System.out.println(ch[i]);
		}
	}
}

Output:

How to Convert a String to UpperCase in Java?

2020-01-08T12:56:00.002+05:30

In the last tutorial, we have learned how to convert a string into a lowercase in Java. We discussed all the two variants to convert all the characters of a string to uppercase. In this tutorial, we will learn how to convert a string to UpperCase in Java. We can convert all the characters of a string to UpperCase by using the toUpperCase() method of Java String Class. Like, toLowerCase() method the toUpperCase() method also has two variants. In this tutorial, we will discuss all the two variants of the toUpperCase() method.

1. toUpperCase(): This is the first variant of toUpperCase() method of String class. This method converts all the characters of a string to UpperCase. This method is equivalent to toUpperCase(Locale.getDefault).

Syntax: The syntax of the first variant of the toUpperCase() method is given below:

public String toUpperCase()

Java program to convert a string to UpperCase

class toUpperCase{
	public static void main(String args[]){
		String str = "String Tutorial BY JavaStudyPoint";
		//converting all the characters of
		//a string into uppercase.
		System.out.println(str.toUpperCase());
	}
}

Output:


STRING TUTORIAL BY JAVASTUDYPOINT

2. toUpperCase(Locale locale): This is the second variant of the Java String toUpperCase() method. This method converts all the characters of a string to UpperCase using to rule of a given locale.

Syntax: The syntax of the second variant of the toUpperCase() method is given below:


public String toUpperCase(Locale locale)

Java String toUpperCase(Locale locale) Method Example


import java.util.Locale;
class toUpperCase{
	public static void main(String args[]){
		String str = "String Tutorial BY JavaStudyPoint";
		
		//Locales with the language "tr"
		//for turkish and "en" for english.
		Locale turkish = Locale.forLanguageTag("tr");
		Locale english = Locale.forLanguageTag("en");
		
		//converting string str into lowercase
		//using turkish and english language.
		String str1 = str.toUpperCase(turkish);
		String str2 = str.toUpperCase(english);
		System.out.println(str1);
		System.out.println(str2);
	}
}

Output:

How to Convert a String into Lowercase in Java?

2020-01-07T22:07:00.004+05:30

In the last tutorial, we have learned Java String's lastIndexOf() method. We have learned all the four variants of this method with an example. In this tutorial, we will learn how to convert a string into lowercase in java. We can convert all the characters of a string into lowercase by using the toLowerCase() method of Java String Class. There are two variants of the toLowerCase() method in Java. In this tutorial, we will discuss all the two variants of this method.

1. toLowerCase(): This is the first variant of toLowerCase() method of string class. This method converts all the characters of a string into lowercase. This is equivalent to calling toLowerCase(Locale.getDefault).

Syntax: The syntax of the first variant of the toLowerCase() method is given below:

public String toLowerCase()

Java program to convert a given string into lowercase

class toLowerCase{
	public static void main(String args[]){
		String str = "String Tutorial BY JavaStudyPoint";
		//converting all the characters of 
		//a string into lowecase.
		System.out.println(str.toLowerCase());
	}
}

Output:


string tutorial by javastudypoint

2. toLowerCase(Locale locale): This is the second variant of the Java String toLowerCase() method. It converts all the characters in this String to lower case using the rule of the given locale.

Syntax: The syntax of the second variant of the toLowerCase() method is given below:


public String toLowerCase(Locale locale)

Java String toLowerCase(Locale locale) Method Example


import java.util.Locale;
class toLowerCase{
	public static void main(String args[]){
		String str = "StrIng TutorIal BY JavaStudyPoint";
		
		//Locales with the language "tr"
		//for turkish and "en" for english.
		Locale turkish = Locale.forLanguageTag("tr");
		Locale english = Locale.forLanguageTag("en");
		
		//converting string str into lowercase
		//using turkish and english language.
		String str1 = str.toLowerCase(turkish);
		String str2 = str.toLowerCase(english);
		System.out.println(str1);
		System.out.println(str2);
	}
}

Output:

Java String lastIndexOf() Method with Example

2020-01-07T16:07:00.000+05:30

In the last tutorial, we have learned all about Java String indexOf() method. We discussed all the four variants of the indexOf() method. In this tutorial, we will learn about the Java String lastIndexOf() method. There are four variants of the lastIndexOf() method. Here, we will discuss all the four variants of the Java String lastIndexOf() method. Let's discuss these four variants one by one.

1. lastIndexOf(int ch): This is the first variant of Java String lastIndexOf() method. This method returns the index of the last occurrence of the specified character. If the specified character is not present there, then it will return -1.

Syntax: The syntax of the first variant of Java String lastIndexOf() method is given below:


public String lastIndexOf(int ch)

Here, ch is a character whose index we want to return.

Java String lastIndexOf(int ch) Method Example


class lastIndexOf{
	public static void main(String args[]){
		String str = "String tutorial by javastudypoint";
	    //returns the last index
		//of specified character.
		System.out.println(str.lastIndexOf('i')); //30
	}
}

Output:

2. lastIndexOf(int ch, int fromIndex): This is the second variant of Java String lastIndexOf() method. This method returns the index of the first occurrence of the specified character, starting the search from the backward specified index. This method return -1 if the specified character is not present there.

Syntax: The syntax of the second variant of Java String lastIndexOf() method is given below:


public String lastIndexOf(int ch, int fromIndex)

Here, ch is a character and fromIndex is the index position at which point the search begins.

Java String lastIndexOf(int ch, int fromIndex) Method Example


class lastIndexOf{
	public static void main(String args[]){
		String str = "String tutorial by javastudypoint";
	    //returns the last index
		//of 'i' before 15th index.
		System.out.println(str.lastIndexOf('i', 15)); //12
	}
}

Output:

3. lastIndexOf(String str): This is the third variant of Java String lastIndexOf() method. This method returns the index of the last occurrence of the specified substring. If the specified substring is not present there, it will return -1.

Syntax: The syntax of the third variant of Java String lastIndexOf() method is given below:


public String lastIndexOf(String str)

Here, str is a substring whose index we want to return

Java String lastIndexOf(String str) Method Example


class lastIndexOf{
	public static void main(String args[]){
		String str = "String tutorial in java by javastudypoint";
	    //returns the last index of
		//initial character of substring.
		System.out.println(str.lastIndexOf("java")); //27
	}
}

Output:

4. lastIndexOf(String str, int fromIndex): This is the fourth variant of Java String lastIndexOf() method. This method returns the index of the first occurrence of the specified substring, starting the search from the backward specified index. This method return -1 if the specified substring is not present there.

Syntax The syntax of the fourth variant of Java String lastIndexOf() method is given below:


public String lastIndexOf(String str, int fromIndex)

Here, str is a substring and fromIndex is the index position at which point the search begins.

Java String lastIndexOf(String str, int fromIndex) Method Example


class lastIndexOf{
	public static void main(String args[]){
		String str = "String tutorial in java by javastudypoint";
	    //returns the last index of
		//initial character of substring
		//before index 30.
		System.out.println(str.lastIndexOf("java", 30)); //27
	}
}

Output:

Java String indexOf() Method with Example

2020-01-07T12:55:00.000+05:30

In the last tutorial, we have learned how to find substring in java. We discussed all the two methods to find the substring in java. In this tutorial, we will learn the string indexOf() method with an example. The string class provides four variants of the indexOf() method. Here, we will discuss all the four variants of the Java String indexOf() method. Let's discuss one by one.

1. indexOf(int ch): This is the first variant of the Java String indexOf() method. This method returns the index of the first occurrence of the specified character. If the specified character is not present there then it will return -1.

Syntax: The syntax of the first variant of the indexOf() method is given below:

public int indexOf(int ch)

Here, ch is a character whose index we want to return.

Java String indexOf(int ch) Method Example


class StringIndexOf{
	public static void main(String args[]){
		String str = "String tutorial by javastudypoint";
	    //returns index of first
		//occurrence of a.
		System.out.println(str.indexOf('a')); //13
	}
}

Output:

2. indexOf(int ch, int fromIndex): This is the second variant of the Java String indexOf() method. This method returns the index of the first occurrence of the specified character, starting the search from the specified index. If the specified character is not present there then it will return -1.

Syntax: The syntax of the second variant of the indexOf() method is given below:


public int indexOf(int ch, int fromIndex)

Here, ch is a character and fromIndex is the index position at which point the search begins.

Java String indexOf(int ch, int fromIndex) Method Example


class StringIndexOf{
	public static void main(String args[]){
		String str = "String tutorial by javastudypoint";
	    //returns index of a
		//after 15th index at position.
		System.out.println(str.indexOf('a', 15)); //20
	}
}

Output:

3. indexOf(String str): This is the third variant of the Java String indexOf() method. This method returns the index of the first occurrence of the specified substring. If the specified substring is not present there then it will return -1.

Syntax: The syntax of the third variant of the Java String indexOf() method is given below:

public String indexOf(String str)

Here, str is a substring whose index we want to return.

Java String indexOf(String str) Method Example


class StringIndexOf{
	public static void main(String args[]){
		String str = "String tutorial by javastudypoint";
	    //returns the index of 
		//initial character of substring 
		System.out.println(str.indexOf("java")); //19
	}
}

Output:

4. indexOf(String str, int fromIndex): This is the fourth variant of the indexOf() method. This method returns the index of the first occurrence of the specified substring, starting the search from the specified index. If the specified substring is not present there then it will return -1.

Syntax: The syntax of the fourth variant of the indexOf() method is given below


public String indexOf(String str, int fromIndex)

Here, str is a substring and fromIndex is the index position at which point the search begins.

Java String indexOf(String str, int fromIndex) Method Example


class StringIndexOf{
	public static void main(String args[]){
		String str = "String tutorial in java by javastudypoint";
	    //returns the index of initial character  
		//of substring after 20th position
		System.out.println(str.indexOf("java", 20)); //27
		
		//returns -1 because specified substring	
		//is not present there. 
		System.out.println(str.indexOf("Java Tutorial", 10)); //-1
	}
}

Output:

27
-1

Java String substring() method with Example

2020-01-06T17:38:00.000+05:30

In the last tutorial, we will learn how to find substring in Java. Basically, there are two forms of the substring method is used to find the substring in Java. In the previous tutorial, we have learned the first form of the substring method. The first of the substring(int startIndex) method, returns a substring from the specified index to the end of the string. But if you want to return a string that allows you to specify both the beginning and ending index of the substring, then we should go for the second form of the substring method.

The second form of the substring(int startIndex, int endIndex) method returns a new string that is a substring of this string. The substring begins at the specified startIndex and extends to the character at index endIndex-1. Like the first form of the substring(int startIndex) method, it throws StringIndexOutOfBoundsException if the startIndex is negative, or endIndex is larger than the length of this String object, or startIndex is larger than endIndex.

Syntax: The syntax of the second form of the substring method is given below:


public String substring(int startIndex, int endIndex)

Here, startIndex specifies the beginning index, and the endIndex specifies the stopping point.

Example of Java substring() Method:

class SubString{
	public static void main(String args[]){
		String str = "String Tutorial by Javastudypoint is best";
		//returns a new string from specified
		//starting index to ending index.
		//returns Tutorial by Javastudypoint
		System.out.println(str.substring(7,33));
		
	}
}

Output:


Tutorial by Javastudypoint

Note: Remember that it throws StringIndexOutOfBoundsException if the startIndex is negative, or endIndex is larger than the length of this String object, or startIndex is larger than endIndex. Let's see the example:


class SubString{
	public static void main(String args[]){
		String str = "String Tutorial by Javastudypoint is best";
	      //throws exception because in this case
		//starting index is larger than 
		//ending index.
		System.out.println(str.substring(33,7));
	}
}

Output:

How to find substring in Java | Java substring() Method

2020-01-06T15:16:00.000+05:30

Because String objects are immutable, whenever you want to modify a String, you must either copy it into a StringBuffer or use one of the following String methods. which will construct a new copy of the string with your modifications complete. In this tutorial, we will learn how to find substring in Java. A substring is a part of the string. The substring(int startIndex) method of the String class is used to find the substring in java. There are two forms of the substring method. Here, we can discuss only the first form and we will discuss the second form in our next tutorial. It throws StringIndexOutOfBoundsException if the specified index is negative or larger than the length of this String object.

Syntax: The syntax of the substring(int startIndex) method in java is given below:


public String substring(int startIndex)

Here, startIndex specifies the index at which the substring will begin. It returns a new string that is a substring of this string. It returns the string from the specified index to the end of the string.

Example of Substring in Java:

class SubString{
	public static void main(String args[]){
		String str = "String Tutorial by Javastudypoint";
		//returns Tutorial by Javastudypoint.
		System.out.println(str.substring(7));
	}
}

Output:


Tutorial by Javastudypoint

Note: Remember that, this method throws StringIndexOutOfBoundsException if the specified index is negative or larger than the length of the string. Let's see the example.


class SubString{
	public static void main(String args[]){
		String str = "String Tutorial by Javastudypoint";
		//throws StringIndexOutOfBoundsException
		//if specified index is negative or 
		//larger than the length of the string.
		System.out.println(str.substring(-1));
		
	}
}

Output:

How to replace a String in Java? | replace() vs replaceAll() vs replaceFirst()

2020-01-04T17:01:00.002+05:30

In the last tutorial, we have learned how to find the length of the string in java. In this tutorial, we will learn how to replace a string in java. The replace() method of String class is used to replace all the occurrences of an old character in this string with a new character.

Syntax: The syntax of the string replace() method is given below:


public String replace(char oldChar, char newChar)

Here, oldChar specifies the characters to be replaced by the character specified by newChar.

Example of Java String replace() Method:


class StringReplace{
	public static void main(String args[]){
		String str1  = "Streng Tutoreal";
		//replacing e with i.
		System.out.println(str1.replace('e', 'i'));
	}
}

Output:


String Tutorial

replaceAll() method in Java

This method returns a String replaces each substring with this string that matches given regular expression with the given replacement.

Syntax: The syntax of the replaceAll() method is given below:


public String replaceAll(String regex, String replacement)

Example of replaceAll() method in Java:


class StringReplace{
	public static void main(String args[]){
		String str1  = "String Tutorial is javastudypoint";
		//replacing all the occurencres of is with by.
		System.out.println(str1.replaceAll("is", "by"));
		//removing all the whitespaces.
		System.out.println(str1.replaceAll("\\s",""));
	}
}

Output:


String Tutorial by javastudypoint
StringTutorialisjavastudypoint.

Remember that, it throws PatternSyntaxException if the regular expression syntax is invalid. Let's see the example.


class StringReplace{
	public static void main(String args[]){
		String str1  = "String Tutorial is javastudypoint";
		//throws PatternSyntaxException
		System.out.println(str1.replaceAll("[", ""));
	}
}

Output:

replaceFirst() method in Java

This method is used to replaces the first substring of this string that matches the given regular expression with the given replacement. It throws PatternSyntaxException if the regular expression is invalid.

Syntax: The syntax of the replaceFirst() method is given below:


public String replaceFirst(String regex, String replacement)

Example of replaceFirst() method in Java:


class StringReplace{
	public static void main(String args[]){
		String str1  = "String Tutorial by author";
		//repalces first occuerence of author with Prashant.
		System.out.println(str1.replaceFirst("author","Prashant"));
	}
}

Output:


String Tutorial by Prashant

How to find String length in Java using length method?

2020-01-04T12:22:00.000+05:30

In the last tutorial, we have learned how to check a string is empty or not. In this tutorial, we will learn how to find the string length in java. We can find string length in java using the length() method of the String class. This method returns the length of the string. Remember that the length variable is used in the array whereas the length() method is used in the string. If you try to use the length variable to find the string length then complier will get a compile-time error.

Syntax: The syntax of the string class length() method is given below:


public int length()

Example of Java String length() Method:


class StringLength{
	public static void main(String args[]){
		String str1 = "Javastudypoint";
		String str2 = "Prashant";
		//14 is the length of the str1.
		System.out.println("The length of the str1 is: "+str1.length());
		//8 is the length of the str2.
		System.out.println("The length of the str2 is: "+str2.length());
	}
}

Output:


The length of the str1 is: 14
The length of the str2 is: 8

Let's see an example of what happened if we are using length variable instead of length() method in case of a string. If you do so, then the compiler will get a compile-time error saying cannot find the symbol. Let's see the example.


class StringLength{
	public static void main(String args[]){
		String str1 = "Javastudypoint";
		String str2 = "Prashant";
		//using length variable instead of length().
		System.out.println("The length of the str1 is: "+str1.length);
		//using length variable instead of length().
		System.out.println("The length of the str2 is: "+str2.length);
	}
}

Output:

Java String isempty() method with Example

2020-01-03T23:24:00.000+05:30

In the last tutorial, we have learned how to compare two strings in Java. In this tutorial, we will learn how to check the string is empty or not. The isEmpty() method of the String class is used to check whether the string is empty or not. If the string is empty then the isEmpty() method returns true otherwise it returns false. In other words, we can say that this method returns true if the string length is 0.

Syntax: The syntax of the isEmpty() of string class is given below:


public boolean isEmpty()

Example of String isEmpty() method in Java:

class StringEmpty{
 public static void main(String args[]){
  // Non-empty string.
  String str1 = "Javastudypoint";
  //empty string.
  String str2 = "";
  //returns false.
  System.out.println(str1.isEmpty());
  //retuens true.
  System.out.println(str2.isEmpty());
 }
}

Output:

How to compare two Strings using equalsIgnoreCase() Method in Java?

2020-01-03T21:24:00.000+05:30

In the last tutorial, We have learned how to compare two strings using equals() method. But there is one limitation of the equals() method. By default equals() method check the content including case also i.e. The comparison is case sensitive. If the comparison is case insensitive it returns false. To overcome this problem we can use the equalsIgnoreCase() method in Java. Let's first see the example of, what the problem to use equals() method.


class StringCompare{
	public static void main(String args[]){
		String str1 = "Javastudypoint";
		String str2 = new String("JAVA");
		String str3 = new String("Javastudypoint");
		String str4 = "Java";
		System.out.println(str1.equals(str3)); //true
		System.out.println(str2.equals(str4)); //false
		System.out.println(str1.equals(str2)); //false
		
	}
}

Output:

true
false
false

The problem with the above code is it check the case also. In the above code, the str2 and the str3 have the same content but the case is different therefore the equals() method returns false.

equalsIgnoreCase() in Java:

To overcome the above problem, we can use the equalsIgnoreCase() method. This method is used to perform the comparison that ignores the case differences. When it compares two strings, it considered A-Z the same as a-z.

Syntax: The syntax of the equalsIgnoreCase() is given below:


public boolean equalsIgnoreCase()

Comparison of two strings using the method equalsIgnoreCase()

Let's understand the equalsIgnoreCase() method in Java with an example.


class StringCompare{
	public static void main(String args[]){
		String str1 = "Javastudypoint";
		String str2 = "javaSTUDYpoint";
		String str3 = "JAVASTUDYPOINT"; 
		String str4 = "Java Tutorial";
               //true because content and case are same
		System.out.println(str1.equalsIgnoreCase(str3));
               //false because content and case are not the same.
		System.out.println(str2.equalsIgnoreCase(str4)); 
               //true because content and case are same
		System.out.println(str1.equalsIgnoreCase(str2)); 
		
	}
}

Output:

How to compare two Strings in Java using equals() Method?

2020-01-03T19:37:00.000+05:30

The Java String class provides several methods to compare the content of the two Strings. We can use equals() method to compare the content of the two strings. It returns true, if the content of the two Strings is the same otherwise it returns false. The equals() method by default check the content including case also i.e. The comparison is case sensitive. If the comparison is case insensitive it returns false. We can discuss the other way to compare the two strings in our next tutorials. Here, we can discuss only the equals() method.

Syntax: The syntax of the equals() method of String class is given below:


boolean equals(Object obj)

Here, obj is the String object being compared with the invoking String object.

Example of compare two Strings by equals() Method

The simple way to compare the two string is by using the equals() method. By default, it checks the content including also case also. Let's see the example.


class StringCompare{
	public static void main(String args[]){
		String str1 = "Javastudypoint";
		String str2 = new String("Java");
		String str3 = new String("Javastudypoint");
		String str4 = "Java";
		System.out.println(str1.equals(str3)); //true
		System.out.println(str2.equals(str4)); //true
		System.out.println(str1.equals(str2)); //false
		
	}
}

Output:

How to Concatenate two Strings using concat() Method in Java?

2020-01-03T15:01:00.000+05:30

We can concatenate two strings in Java by using concat() method of String class. It concatenates the specified string to the end of this string. If the length argument of the string is 0 then this string object is returned otherwise a new string object is created.

Syntax: The syntax of the concat() method in java is given below:

public String concat(String str)

Here str, specifies the string to be concatenated at the end of another string.

String Concatenate in Java by using concat() Method

We can concatenate the two string by using concat() method. It returns the newly created string object. Let's see the example.


class charAtExample{
	public static void main(String args[]){
		String str = "Java";
		String str1 = str.concat("studypoint"); //concat the string
		System.out.println("The newly concatenated string is: " +str1);
	    
	}
}

Output:

Java String Class charAt() Method with Example

2020-01-03T13:06:00.000+05:30

The charAt() method of String class is used to return the char value at the specified index. An index ranges from 0 to length() - 1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing. If the specified index is not there then you will get StringIndexOutOfBoundExceptions: string index out of range.

Syntax: The syntax of the String class charAt() method is given below.


public char charAt(int index)

Here, the index is the index of the character that you want to obtain. The charAt() method returns the character at the specified position.

Java String Class charAt() method Example.

Let's understand the String charAt() method with an example.


class charAtExample{
	public static void main(String args[]){
		String str = "Javastudypoint";
	    char ch = str.charAt(7); //returns the char value at 7th index.
	    System.out.println("The value at 7th index is: " +ch);
	}
}

Output:

 The value at 7th index is: d

StringIndexOutOfBoundsException with charAt() Method.

The charAt() method of String class throws StringIndexOutOfBoundsException if the specified index argument is negative or the greater of the length of the string. Let's see the example.

Case 1: When the index argument is greater than the length of the string.


class charAtExample{
	public static void main(String args[]){
		String str = "Javastudypoint";
	    char ch = str.charAt(20); //StringIndexOutOfBoundsException
	    System.out.println("The value at 7th index is: " +ch);
	}
}

Output:

Case 2: When the index argument is negative. Let's see the example.


class charAtExample{
	public static void main(String args[]){
		String str = "Javastudypoint";
	    char ch = str.charAt(-10); //StringIndexOutOfBoundsException
	    System.out.println("The value at -10th index is: " +ch);
	}
}

Output:

String Class in Java | Why String is Immutable in Java?

2020-01-03T00:49:00.001+05:30

In Java, a string is a sequence of characters. But, unlike many other languages that implement strings as character arrays, Java implements strings as objects of type string. String class in Java is defined in the java.lang package. Thus, this class available to all the programs automatically. When you create a String Class object, you are creating a string that cannot be changed. Hence, the objects of the String class are immutable.

What is String immutability?

String objects in Java are immutable that means you cannot change the content of a string once they created. Let's understand the concept of string immutability with an example. In this example, we created a string object with the help of a new keyword that contains the string "Java" and in the next statement, we want to concat this string with other string "Tutorial".

But when we concat the string a new object will be created in the existing object, and we can't able to perform any changes. When we concat "Java" with "Tutorial" it will become Java Tutorial. But this new object is not assigning with any reference variable then automatically this object eligible for the garbage collector. That's why we will get only "Java" as an output. See the image given below:


class StringExample{
	public static void main(String args[]){
		String str = new String("Java");
	    str.concat("Tutorial");
	    System.out.println(str);
	}
}

Output:

Java

How to create a string object in Java?

We can create a string object in java by using two ways:
1. By using String literals.

2. By using the new Keyword.

1. By using String literals: We can create a string object by using string literals. In String literals, we can create a string by using double-quotes. For example:


String str = "Javastudypoint";

Each time when you create a String by using String literal, the JVM first checks whether the object is present in the string pool or not. If it is already present then the same reference is returned otherwise a new object will be created in the string pool and then return the reference.

2. By using the new keyword: When we create a String using the new keyword, the JVM creates a new String object in heap memory and the String literal "Javastudypoint" will be placed inside the String pool and the variable str will refer to the String object in heap.


String str = new String("Javastudypoint");

Advantage of String Constant Pool:

The biggest advantage of String constant pool is the same object can be reused multiple times instead of creating new objects. Therefore memory will be saved and performance will be improved.

Disadvantage of String Constant Pool:

As we know, because of the string constant pool one object can be reused by multiple references. If one reference any person can try to change then all the remaining references can be affected this is the biggest disadvantage of String Constant Pool.

Why String class objects are immutable?

The meaning of the immutable string is once we create a string its value cannot be changed. The String is immutable in nature because it uses the concept of String literals. Let's take an example to understand this:
String str1 = "Java";
String str2 = "Java";
In this example, the two reference variables refer to the same object. if one reference variable changes the value of the object(suppose "java" to "python"), It will affect to all the reference variable. That's why the String object is immutable in nature.

Java String class constructors:

The String class in java supports several constructors. The most commonly used constructors are given below:

1. String(): Initializes a newly created String object so that it represents an empty character sequence. For example:

 String str = new String();

2. String(char chars[]): This constructor can be used to create a string initialized by an array of characters. For example.


char chars[] = {'a', 'b', 'c'};
String str = new String(chars);  //abc

3. String(char chars[], int startIndex, int numChars): This constructor can be used to specify a subrange of a character array as an initializer. Here, startIndex specifies the index at which the subrange begins, and numChars specifies the number of characters to use. For example.


char chars[] = {'a', 'b', 'c', 'd', 'e', 'f'};
String str = new String(chars, 2, 3);  //cde.

4. String(String strObj): We can use this constructor to construct a String object that contains the same character sequence as another string object. Here, stringObj is a string object. For example.


char ch[] = {'J', 'a', 'v', 'a'};
String str1 = new String(ch);  //Java.
String str2 = new String(str1); //Java.

5. String(byte[] b ): This constructor is used to create a new string object by decoding the byte array. These byte values are converted into corresponding characters. For example.


byte[] b = {97, 98, 99, 100);
String str = new String(b);
System.out.println(str); //abcd

6. String(StringBuffer buffer): This constructor is used to create a new string that contains the sequence of characters currently contained in the StringBuffer argument. For example.


StringBuffer buffer = new StringBuffer("Javastudypoint");
String str = new String(buffer); // Javastudypoint

7. String(StringBuilder builder): This constructor is used to create a new string that contains the sequence of characters currently contained in the StringBuilder argument. For example.


StringBuilder builder = new StringBuilder("Javastudypoint");
String str = new String(builder); // Javastudypoint

String class Methods in Java

The String Class in Java provides many methods. The most commonly used methods are given below. We can discuss each method in detail in our next tutorials. Here, we can only introduce these methods.

1. char charAt(int index): This method is used to return the char value at the specified index. If the specified index is not there then you will get StringIndexOutOfBoundExceptions: string index out of range.

2. String concat(String str): This method is used to concatenates the specified string to the end of this string.

3. boolean equals(Object obj): This method is used for content comparison. It is the overriding method of the object class. The equals() method by default check content including case also i.e. The comparison is case sensitive. If the comparison is case insensitive then this method returns false.

4. boolean equalsIgnoreCase(String str): This method is used to perform the comparison that ignores the case differences. When it compares two strings, it considered A-Z to the same as a-z.

5. boolean isEmpty(): This method is used to check whether the string is empty or not. If the string is empty, it returns true else it returns false.

6. int length(): This method is used to returns the number of characters in the string. Remember that the length variable is used for array and the length() method is used for String. If you can use the length variable to find the length of the string then the compiler will get a compile-time error.

7. String replace(char oldChar, char newChar): This method is used to replacing all the occurrences of the oldChar in this string with newChar.

8. String substring(int startIndex): This method returns the string from the beginning index to the end of the string. Here, startIndex specifies the index at which the substring will begin.

9. String substring(int startIndex, int endString): This method returns String from the beginning index, up to, but not including, the ending index.

10. int indexOf(int ch): This method returns the index of the first occurrence of the specified character. If the specified character is not present there then it returns -1.

11. int lastIndexOf(int ch): This method returns the index of the last occurrence of the specified character.

12. int indexOf(int ch, int fromIndex): This method returns the index of the first occurrence of the specified character, starting the search from the specified index.

13. int lastIndexOf(int ch, int fromIndex): This method returns the index of the last occurrence of the specified character, starting the search from the backward specified index.

14. int indexOf(String str): This method returns the index of the first occurrence of the specified substring.

15. int lastIndexOf(String str): This method returns the index of the last occurrence of the specified substring.

16. int indexOf(String str, int fromIndex): This method returns the index of the first occurrence of the specified substring, starting the search from the specified index.

17. int lastIndexOf(String str, int fromIndex): This method returns the index of the last occurrence of the specified substring, starting the search from the backward specified index.

18. String toLowerCase(): This method converts all the characters in a string from uppercase to the lowercase.

19. String toUpperCase(): This method converts all the characters in a string from lowercase to the uppercase.

20. String trim(): This method returns the copy of the string by removing whitespaces at both ends. It doesn't remove the whitespaces in the middle.

21. char[] toCharArray(): This method is used to convert a string into a char array.

22. int compareTo(String str): This method is used to compare the two strings lexicographically. It returns a positive number, negative number or 0.

Array in Java with Example | How to Initialize Array in java

2019-12-28T15:39:00.000+05:30

Array in Java is an object that holds multiple values in a single variable. The array can hold the value of only a similar data type. If you want to represent the huge number of values by using a single variable then you can go for Array. We can create an array of any type and may have one or more dimensions. The length of an array is established when an array is created. After creation, the length of the array is fixed. Array in Java is based on the index. Each item in an array called an element, and each element is accessed by its index number. The index number begins with 0 and the 9th element, for example, would, therefore, be accessed at index 8.

Advantages of Array:

1. We can represent a huge number of values by using a single variable.
2. We can easily search any element of an array by using the index number.

Disadvantages of Array:

1. Arrays are fixed in size. The length of an array is established when an array is created. Once we create an array with some size then there is no chance of increasing or decreasing the size of an array based on our requirements.
2. Arrays can hold only homogenous data type of elements.

Note: To overcome the limitation of an array we should go for collection in Java.

Types of Array in java:

There are two types of Array in Java:
1. One-dimensional Array.
2. Multidimensional Array.

How to declare Array in Java?

We can declare an array by using different ways. The general form of a one-dimensional array declaration is:


data-type[] variable-name; Or
data-type []variable-name; Or
data-type variable-name[];

All the above-mentioned declaration is valid. You can use any one of the above declarations. Here data-type describe the what type of data the array will hold and variable-name describe the reference of the array.

How to instantiate an Array in Java?

Once an array is declared, the only reference of an array is created. But you need to use it now to allocate memory for arrays. We can use the new keyword to instantiate an array. The general form of instantiating an array appears as follows:


variable-name = new data-type[size];

Here data-type specifies the type of data being allocated, size specifies the number of elements in the array, and variable-name specifies the reference of an array that is referred to the array.

How to initialize an array in Java?

Arrays can be initialized when they declared or later in the program as per your requirements. We can initialize the array by a list of comma-separated expressions surrounded by curly braces. The commas separate the value of the array elements. The general form of one-dimensional array initialization is as follows:


int array[] = {10, 20, 40, 50}; OR
arrayRefvarName[index-number] = value;

Example of Array in Java

Let's understand the concept of an array with an example. In this example, we create an array of int type, we initialize the array and traverse the array to print the values of array.


class ArrayExample{
	public static void main(String args[]){
		//Array declaration.
		int[] array;
		
		// Array instantiate.
		array = new int[5];
		
		//Array initialization.
		array[0] = 10;
		array[1] = 20;
		array[2] = 30;
		array[3] = 40;
		array[4] = 50;
		
		//traverse the array.
		for(int i = 0; i<array.length;i++){
			System.out.println("Element at index " +i+ " is: " +array[i]);
		}
	}
}

Output:


Element at index 0 is: 10
Element at index 1 is: 20
Element at index 2 is: 30
Element at index 3 is: 40
Element at index 4 is: 50

Multidimensional Array in Java:

Multidimensional Arrays in Java are actually arrays of arrays. The elements of a multidimensional array are stored in the form of row and column also known as matrix form

How to declare a Multidimensional Array in Java?

The general form of declaration of Multidimensional Array is as follow:


data-type[][] arrayRefVarName; (OR)
data-type arrayRefVaName[][];  (OR)
data-type [][]arrayRefVarName;

How to instantiate a Multidimensional Array?

Once an array is declared, the only reference of an array is created. But you need to use it now to allocate memory for arrays. The general form of instantiating a Multidimensional array appears as follows:


int[][] array = new int[2][2] //2 row & 2 column

How to initialize a Multidimensional array in Java?

Multidimensional Arrays can be initialized when they declared or later in the program as per your requirements. The general form of multidimensional array initialization is as follows:


int[][] array = {{1,2,3}, {4,5,6}, {7,8,9}};

Example of Multidimensional Array in Java:

Let's see a simple example to understand the Multidimensional array. In this example, we declare and initialize the multidimensional array and we can also print the value of this array in the form to row and column.


class ArrayExample{
	public static void main(String args[]){
		
		//Declaration and initialization.
		// of 2-D array
		int[][] array = {{1,2,3}, {4,5,6}, {7,8,9}};
		
		//loop for row and column.
		for(int i=0; i<3; i++){
			for(int j=0;j<3;j++){
				//print the elements of 2-D array.
				System.out.print(array[i][j] + " ");
			}
			System.out.println();
		}
	}
}

Output:


1 2 3
4 5 6
7 8 9

How to copy data from one array to another?

The System class has an arraycopy method that you can use to efficiently copy data from one array into another. The syntax is given below:


public static void arraycopy(Object src, int srcPos,
                             Object dest, int destPos, int length);

The two Object arguments specify the array to copy from and the array to copy to. The three int arguments specify the starting position in the source array, the starting position in the destination array, and the number of array elements to copy.

Example of copying an array in java:

In this example, we can declare an array of char elements. It uses the System.arraycopy method to copy a subsequence of array component into the second array. Let's see the example.


class ArrayCopy{
    public static void main(String[] args){
		
		//declaring a source array.
        char[] copyFrom = { 'd', 'e', 'j', 'a', 'v', 'a', 's',
			    't', 'u', 'd', 'y', 'p', 'o','i','n','t'};
				
		 //declaring a destination array.		
        char[] copyTo = new char[14];
		
         //copying an array using arraycopy method.
        System.arraycopy(copyFrom, 2, copyTo, 0, 14);
		
		 //printing the destination array.
        System.out.println(new String(copyTo));
    }
}

Output:


javastudypoint

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Interface in Java with Example - Multiple Inheritance using Interface

2019-12-27T10:57:00.000+05:30

An interface in java is syntactically similar to classes, but they do not have instance variable and their method are declared without any body. The methods declared inside an interface are by default abstract(only method signature, not implementation) and the variables declared inside an interface are public, static, and final by default. The interface in java is a mechanism to achieve abstraction. Once an interface is defined, any number of classes can implement this interface. Also, one class can implement any number of interfaces.

Why interface in java is used.

1. An interface in Java can be used to achieve total abstraction(100 % abstraction).
2. As we know, Java does not support multiple inheritance in the case of class but using the interface we can achieve multiple inheritance in java.
3. It can also be used to achieve loose coupling.

How to define an Interface.

An Interface is defined much like a class. It can have methods and variables like class. But in Interface, all the methods are by default abstract and all the variables are by default public static, and final. This is the general form of an interface:


interface name{
  return-type method-name1(parameter-list);
  return-type method-name2(parameter-list);
  type varname1 = value;
  type varname2 = value;
  //.....
  return-type method-nameN(parameter-list);
  type varnameN = value;
}

How to implement an Interface.

Once an interface has been defined, one or more classes can implement that interface. To implement an interface, include the implements clause in a class definition, and create the methods defined by the interface. The general form of a class that includes the implements clauses look like this:


class classname implements interface-name{
    // class body
}

To implement an interface, a class must create a complete set of methods defined by the interface. However, each class is free to determine the details of its own implementation. If a class implements more than one interface, then the interfaces are separated with a comma.

Example of Interface in Java:

Let's understand the interface with the help of a real-world example of banks like PNB, SBI, OBC, etc. they have common functionality such as rate of interest. So we can make an interface and put all the common functionality inside this interface, and lets PNB, SBI, and OBC, etc implement these functionalities in their own class in their own way.


interface Bank{
	float rateOfInterest();
}
class PNB implements Bank{
	public float rateOfInterest(){
		return 9.5f;
	}
}
class SBI implements Bank{
	public float rateOfInterest(){
		return 8.5f;
	}
}
class OBC implements Bank{
	public float rateOfInterest(){
		return 7.5f;
	}
}
class InterfaceExample{
	public static void main(String args[]){
		Bank b = new PNB();
		System.out.println("Rate of interest of PNB is: " +b.rateOfInterest());
	}
}

Output:

Rate of interest of PNB is: 9.5

Multiple Inheritance by using the interface in java:

As we know, we cannot achieve multiple inheritance in the case of class because of the ambiguity problem. but using the interface we can achieve multiple inheritance in java. Let's see the example.

Java program for multiple inheritance using interface:


interface InterfaceOne{
	public void display();
}
interface InterfaceTwo{
	public void display();
}
class Main implements InterfaceOne,InterfaceTwo{
	public void display(){
		System.out.println("Display() method implementation");
	}
	public static void main(String args[]){
		Main obj = new Main();
		obj.display();
	}
}

Output:

Display() method implementation

Interface and Inheritance:

As we know, A class can implement an interface but an interface cannot implement another interface. One interface can extend another interface. One interface can extend another interface by use of extends keyword. The syntax is the same as for inheriting the classes. When a class implements an interface that inherits another interface, it must provide the implementation for all methods defined within the interface. Let's see the example:


interface InterfaceOne{
	public void display();
}
interface InterfaceTwo extends InterfaceOne{
	public void show();
}
class Main implements InterfaceTwo{
	public void display(){
		System.out.println("Display() method implementation.");
	}
	public void show(){
		System.out.println("Show() method implementation.");
	}
	public static void main(String args[]){
		Main obj = new Main();
		obj.display();
		obj.show();
	}
}

Output:


Display() method implementation.
Show() method implementation.

Access Modifiers in Java - Private, Default, Protected, Public Modifiers

2019-12-26T17:53:00.002+05:30

Access Modifiers in Java are used to restricts access of a class, constructor, data member, and method in another class. There are four types of access modifiers available in Java:

1. Private Access Modifier.
2.Default Access Modifier.
3. Protected Access Modifier.
4. Public Access Modifier.

Access Modifiers Table: Let's understand Java access modifiers with the help of the table.

1. Private Access Modifier:

The private access modifier is only accessible within the same class in which they are declared. The data member and method declared as private cannot be accessed from outside the class. If you try to access the private data member and method from outside the class then the compiler will give you a compile-time error.

Example of Private Access Modifier:

class PrivateModifier{
	private int num = 10;
	private void display(){
		System.out.println("Value of num is: " +num);
	}
}
class AccessModifiers{
	public static void main(String args[]){
		PrivateModifiers obj = new PrivateModifiers();
		System.out.println(obj.num);
		obj.display();
	}
}

Output:


Compile time error:
error: num has private access in PrivateModifier(class)
          System.out.println(obj.num);
error: display() has private access in PrivateModifier(class)
          obj.display();

2. Default Access Modifier:

The class, data member, and method that are not declared using any modifier, it treated as default access modifier by default. The default access modifier will be accessible within the same package. If you try to access the default modifier from outside the package then the compiler will give you a compile-time error.

Example of Default Access Modifier:

In this example, we will create two packages pack1 and pack2 and the classes inside the packages are default access modifier and we accessing the class A from outside the package. Since class A is not public therefore it cannot be accessible from outside the package.


//save by A.java
package pack1;
class A{
	void display(){
		System.out.println("Inside class A method. ");
	}
}


//save by B.java
package pack2;
import pack1.*;
class B{
	public static void main(String args[]){
		A obj = new A();
		obj.display(); //compile-time error.
	}
}

Output:


compile time error.

3. Protected Access Modifier:

The data member and method declared as protected can be only accessible within the same package and outside the package through inheritance only. It cannot be applied to classes.

Example of Protected Access Modifier:

In this example, we will create two packages pack1 and pack2 and class A in the package pack1 is made public so it can be accessed from outside the package but the method display() declared inside this package is protected, so it can be accessed from outside the class through inheritance only.


//save by A.java
package pack1;
class A{
	protected void display(){
		System.out.println("Inside class A method. ");
	}
}


//save by B.java
package pack2;
import pack1.*;
class B extens A{
	public static void main(String args[]){
		B obj = new B();
		obj.display(); 
	}
}

Output:


inside class A method.

4. Public Access Modifier:

The members, methods, and classes declared as public can be accessed from anywhere. This modifier can be accessed from within the class, outside the class, within the package, and outside the package.

Example of Public Access Modifier:

In this example, we will create two packages pack1 and pack2 and class A and method display() inside the package pack1 is public, so it can be accessed from anywhere.


//save by A.java
package pack1;
public class A{
	public void display(){
		System.out.println("Inside class A method. ");
	}
}


//save by B.java
package pack2;
import pack1.*;
class B{
	public static void main(String args[]){
		A obj = new A();
		obj.display(); //compile-time error.
	}
}

Output:


inside class A method.

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Packages in Java | How to create and use Packages in Java

2019-12-25T23:12:00.000+05:30

A package in java is defined as the group of related classes and interfaces into a single unit. For example: Suppose you want to perform database operations, the required classes and interfaces are grouped into a single unit which is java.sql package. Therefore we can say that packages are the encapsulation mechanism to group related classes and interfaces into a single unit. There are two types of packages in Java: built-in packages and user-defined packages.

Advantages of using Packages in Java:

1. Naming Conflicts: There are 2 Date classes available in Java, one inside the SQL package and second inside the util package. So, by using the packages we can able to differentiate java.util.date and java.sql.Date. If a package statement is not there than it is impossible to have 2 date classes. By using a package, we can able to resolve naming conflicts.

2. Modularity and Maintainability: As we know, Packages are the group of related classes and interfaces, therefore, Modularity and the Maintainability of the application are gone to be improved.

3. Security: Suppose you have a class inside a package pack1. Assume this class is not public if it is not public then outside person not able to access this class because the default is only accessible within the same package. The package provides security to our component.

Types of packages in Java.

There are two types of packages in Java:

1. Built-in package: The packages which are already defined and part of Java API is known as Built-in packages. Some commonly used built-in packages are given below:

i) java.lang: This package contains language support classes.

ii) java.util: This package contains utility classes such as LinkedList, Dictionary, etc.

iii) java.io: This package contains classes for file read/write operations.

iv) java.net: This package contains classes for networking operations.

v) java.applet: This package contains classes for creating the applets.

2. User-defined package: The packages that are defined by the user is known as a user-defined package.

How to create packages in Java.

Creating a package in Java is not a difficult task. You can create a package in java by using the package keyword. for example:


package MyPackage;

Here package is a keyword and MyPackage is a package name.

How to compile and run Java Package.

Suppose we have a file called HelloWorld.java, and we want to put this file in a package world. for example:


package World;
public class HelloWorld{
	public static void main(String args[]){
		System.out.println("Hello World");
	}
}

Now compile this file as:


javac -d . HelloWorld.java

Here -d specifies the destination where to put the class file and . (dot) specifies the current working directory.

You can run this file as:


java World.HelloWorld

We need to use the fully qualified name to run the class. Here World is a package and HelloWorld is a class inside this package.

How to access the package from another package.

There are three ways to access the package from another package.
1. import package.*;
2. import package.classname;
3. using a fully qualified class name.

1. Using a package name:

If we use package.* then all the classes and interfaces of this package accessible. We can use the import keyword to access the classes and interfaces of another package to the current package. Let's see the example.

**Example of Java package that imports the package-name.*;**


//save by class1.java.
package pack1;
public class Class1{
	public void display(){
		System.out.println("Inside class1 method.")
	}
}


//save by Class2.java
package pack2;
import pack1.*;
class Class2{
	public static void main(String args[]){
		Class1 obj = new Class1();
		obj.display();
	}
}

Output:


Inside class1 method.

2. Using the package.classname:

We can use the import package.classname to access the only declared class of this package. Let's see the example.

Example of the package in java using the package.classname


//save by class1.java.
package pack1;
public class Class1{
	public void display(){
		System.out.println("Inside class1 method.")
	}
}


//save by Class2.java
package pack2;
import pack1.Class1;
class Class2{
	public static void main(String args[]){
		Class1 obj = new Class1();
		obj.display();
	}
}

Output:


Inside class1 method.

3. Using a fully qualified class name.

If we use a fully qualified class name then only declared class of this package will accessible and there is no need to import. In this case, we need to use a fully qualified name every time when you are accessing the class or interface.

Example of a package in Java using a fully qualified class name:


//save by class1.java.
package pack1;
public class Class1{
	public void display(){
		System.out.println("Inside class1 method.")
	}
}


//save by Class2.java
package pack2;
class Class2{
	public static void main(String args[]){
                //using fully qualified class name.
		pack1.Class1 obj = new pack1.Class1(); 
		obj.display();
	}
}

Output:


Inside class1 method.

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