Extreme Java

How to use Verbose options in Java

2012-11-29T11:08:00.000+05:30

When running a Java program, verbose options can be used to tell the JVM which kind of information to see. JVM suports three verbose options out of the box. As the name suggests, verbose is for displaying the work done by JVM. Mostly the information provided by these parameters is used for debugging purposes. Since it is used for debugging, its use is in development. One would never have to use

How String equals method works

2012-11-18T22:44:00.001+05:30

equals method is declared in Object class and hence is inherited by all classes in Java. The purpose of equals method is to provide logical equality. The default implementation of equals method is: public boolean equals(Object obj) { return (this == obj); } Thus the default behavior of equals method is same as == operator. equals method in String class checks if the two strings have same

Overflow And Underflow of data types in Java

2012-11-10T12:56:00.000+05:30

Overflow and underflow of values of various data types is a very common occurence in Java programs. This is usually because the beginners dont' pay proper attention to the default values of various data types. If we are creating a byte type variable and assigning it a value, we should be aware that the value will be treated as an int and hence a potential overflow condition. In Java the overflow

Java HashMap Working

2012-07-15T20:38:00.000+05:30

Hash based collections in Java work on same concepts. There are a few things to keep in mind when working with them. The details listed in this article will help you to make your programs efficient and easy to maintain. I will describe the internal details of HashMap followed by some tips. Though I am choosing HashMap here but this discussion is applicable to all collection classes.

How to set Session Attributes in Java,set Session Attribute

2012-04-28T22:31:00.000+05:30

Session set Attribute Attributes are a way to store information in a Java web application for later use. By setting attributes inside a web application, one can keep the information till the point the user is active in the application. Session attributes are created for individual users and destroyed when the user session gets destroyed. The following code example shows how to get session

Invoke methods of an object using reflection

2012-04-27T21:43:00.000+05:30

How to invoke methods of class using reflection Reflection helps in getting all the information of a class from a Java program. The use of reflection also helps in invoking the methods present in a class by passing the appropriate arguments when invoking the method. The following program shows how methods of a class can be invoked by using reflection in Java. package com.example; import

How to invoke a Java application from JAR file

2012-04-26T20:45:00.000+05:30

Running JAR Files as Applications If there is a JAR file which you want to run as a Java application then there is an option to do so by using java command line tool. java -jar jar-file The -jar flag tells the interpreter that the application is packaged in the JAR file format. For running the above command, one has to make sure that a class with main method exists and the same has been

Some important points to note about Wrapper Classes

2012-04-25T20:33:00.000+05:30

How to use wrapper classes in Java Wrapper classes are just normal classes but they have gained significance because of there close association with primitive data types. Here are some important points to note about wrapper classes in Java. 1) Wrapper classes were introduced in JDK1.5 2) Wrapper classes are Immutable 3) Wrapper classes were introduced so that primitive data types could be

String class constructors,Constructors present in String class

2012-04-24T20:26:00.000+05:30

String Constructors in Java Strings are almost unavoidable in any kind of application. The String class in Java provides a number of ways for creating instances of String class. This includes the overloaded constructors, de-serialization and string literals. Here we will see all the overloaded constructors which are present in the String class in Java: String() Initializes a newly created

Replace a String at multiple places in another string

2012-04-23T16:19:00.000+05:30

Replace a String at multiple places in another string String class in Java provides a number of powerful API method for string manipulation in Java. This includes replacing all occurrences of a string by another in a parent string in Java. package com.example; /** This class is a demo for Java Tutorial on how to replace all occurrences of a substring in Java * * @author Extreme Java *

Parse Comma Delimited List

2012-04-22T14:43:00.000+05:30

Parse Comma Delimited List Parsing the contents of string having some delimiter is a common task to be performed in a Java application. There are multiple ways in which strings can be parsed on the basis of delimiter in Java which includes the split method of String class and the StringTokenizer class The following Java program parses a comma separated list of strings and then splits it based

Count number of occurrences of substring in a string

2012-04-21T12:00:00.000+05:30

Count number of occurrences of substring in a string There is no direct API method present in the String class which can count the number of occurrence of a substring in another string and return the count. But there are other API methods which can help in counting the number of times one string occurs in other string. The following code does the job of counting the search string in parent

equals() vs == in Java Strings,Compare Strings in Java

2012-04-20T11:13:00.000+05:30

equals() vs == in Java Strings equals method is declared in Object class and hence is available to all classes including the String class. But String class overrides the equals method to check for the equality of string content. On the other hand the default behaviour of equals method and == operator is same which is to check if the two references are pointing to the same object or not. Thus if

String HashCode,hashcode() method in String class Java

2012-04-19T22:39:00.000+05:30

String HashCode Hashcode is an important aspect of programs which use hash based collections like HashMap, Hashtable or HashSet. The String class's objects are very frequently used as keys for key,value pairs. The following code shows how the hashcode method of String class looks like: /** * Returns a hash code for this string. The hash code for a * String object is computed as

String concatenation in System.out.println(),Concatenate Strings

2012-04-18T22:38:00.000+05:30

String concatenation in System.out.println() The + operator is overloaded for performing the concatenation operation in Java. When used in System.out.println() then it automatically invokes the toString method and then uses the + operator to concatenate the strings being used with + operator. package com.example; /** This class is a Java tutorial for concatenation of Strings in Java * * @

Remove leading and trailing white space from string

2012-04-17T22:37:00.000+05:30

Remove leading and trailing white space from string The following program shows how to use regular expressions for trimming leading and trailing spaces in a string object. package com.example; /** This class is a Java tutorial for triming left and right spaces in Java * * @author Extreme Java */ public class Test{ /** This method shows how to trim white spaces in Java * * @param args */

Compairing String and StringBuffer contents,Compare Strings

2012-04-16T22:35:00.000+05:30

Comparing String and StringBuffer contents StringBuffer class's objects act like a buffer for adding string contents. As very popularly known that StringBuffer objects are mutable and modifying the contents of string buffer doesn't create new objects. But sometimes, one requires to compare the contents of String object with the contents of StringBuffer object. package com.example; /** This

Autoboxing and Auto-Unboxing,How to autobox and auto-unbox

2012-04-15T22:35:00.000+05:30

Autoboxing and Auto-Unboxing Autoboxing and auto-unboxing is a very useful feature added to JDK which automatically makes sure that primitive to wrapper happens whenever there is a need to do so. The following program shows how auto-boxing and auto-unboxing works in Java programs: package com.example; /** This class is a Java tutorial for auto-boxing and auto-unboxing in Java * * @author

Alternatives to JUnit for unit testing

2012-04-14T22:33:00.000+05:30

Alternatives to JUnit for unit testing JUnit is very popular unit testing framework for Java projects. The best part of it is that Eclipse IDE comes with built in suport for latest version of JUnit. But still there are some features which are not right now available in JUnit and alternatives have been developed for the same. The following list shows some of the best alternatives for JUnit which

Widening and Narrowing conversion in Java,Type Conversion in Java

2012-04-13T22:32:00.000+05:30

Widening and Narrowing conversion in Java In Java data types can be converted from one form to another. But since each data type has a range of values which can be assigned and the use of type casting and assignment from wider and narrow data types can happen. For example int and long are compatible data types where int value can be assigned to long variable and long value to an int variable.

Toggle String case in Java,Lower Upper Case in Java Program

2012-04-12T16:01:00.000+05:30

Toggle String case in Java The String class API allows for changing the case of a String to upper or lower case. However there is no method for detecting the case and then change the case accordingly. One can use the Character class to detect the case and then toggle the case of each of the character present in the String. package com.example; /** This class is a Java tutorial for toggling

Using lastIndexOf in Strings Java,get Character from String

2012-04-11T15:59:00.000+05:30

How to use lastIndexOf in String class The String API has methods for searching a particular character starting from reverse of the String. The method lastIndexOf is used to find the last occurrence of a character in a String. Once you get the index of last occurrence, simply get the character using charAt method which accepts integer index as argument. package com.example; /** This class is a

Convert String to character array to String

2012-04-10T15:57:00.000+05:30

Convert String to character array to String The String class internally uses the character array for storing the characters present in the string. This means that we can convert a String object into character array and also convert a character array to String object. The code to convert a character array to String is shown below: public class MyTest{ public static void main(String[] args) {

How to create custom annotation in Java

2012-04-09T15:55:00.000+05:30

How to create custom annotation in Java Annotations were introduced in JDK 1.5 and act like meta data. In this tutorial, we will see how to create a new annotation and then use it in other classes. The following code shows how to create annotation in Java. public @interface MyAnnotation { public String str1(); public String str2(); } In order to apply the above annotation to

How to capitalize the first character of string

2012-04-08T21:02:00.000+05:30

How to capitalize the first character of string If you are searching for the logic to automatically capatializing the first character of a string then the code shown below should be used to do so. package com.example; /** This class is a Java tutorial for making the first character as capital in Java * * @author Extreme Java */ public class Test{ /** This method shows how to