Programming with Java

New Features in Java

2014-06-02T12:07:00.002+05:30

New Features in Java

There are many new features that have been added in java. There are major enhancement made in Java5, Java6 and Java7 like auto-boxing, generics, var-args, java annotations, enum, premain method etc.

Most of the interviewers ask questions from this chapter.

Do You Know ?

1. How to create generic class and generic method in java ?

2. What is annotation and how to create custom annotation ?

3. What is the advantage of assertion and where we should not use it ?

4. What is variable argument and what rules are defined for variable argument ?

5. What is the difference between import and static import ?

6. How autoboxing is applied in method overloading. Which concept beats autoboxing ?

7. What is enum type and how to specify specific value to the enum constants ?

J2SE 4 Features

The important feature of J2SE 4 is assertions. It is used for testing.

Assertion (Java 4)

J2SE 5 Features

The important features of J2SE 5 are generics and assertions. Others are auto-boxing, enum, var-args, static import, for-each loop (enhanced for loop etc.

For-each loop (Java 5)
Varargs (Java 5)
Static Import (Java 5)
Autoboxing and Unboxing (Java 5)
Enum (Java 5)
Covariant Return Type (Java 5)
Annotation (Java 5)
Generics (Java 5)

JavaSE 6 Features

The important feature of JavaSE 6 is premain method (also known as instrumentation).

Instrumentation (premain method) (Java 6)

JavaSE 7 Features

The important features of JavaSE 7 are try with resource, catching multiple exceptions etc.

String in switch statement (Java 7)
Binary Literals (Java 7)
The try-with-resources (Java 7)
Caching Multiple Exceptions by single catch (Java 7)
Underscores in Numeric Literals (Java 7)

JavaSE 8 Features

Let’s look at 5 features that we feel are an absolute must for you to know about:

1. Lambda expressions

Even if we really didn’t want to go mainstream here, there’s little doubt that from a developer’s perspective, the most dominant feature of Java 8 is the new support for Lambda expressions. This addition to the language brings Java to the forefront of functional programming, right there with other functional JVM-based languages such as Scala and Clojure.

We’ve previously looked into how Java implemented Lambda expressions, and how it compared to the approach taken by Scala. From Java’s perspective this is by far one of the biggest additions to the language in the past decade.

At minimum, it’s recommended you become familiar with the Lambda syntax, especially as it relates to array and collection operations, where Lambdas have been tightly integrated into the core language libraries. It is highly likely that you’ll start seeing more and more code like the snippet below in both 3rd party and within your organization’s code.

view source

print?

1.Map<Person.Sex, List<Person>> byGender =

2.roster.stream().collect(Collectors.groupingBy(Person::getGender));

* A pretty efficient way of grouping a collection by the value of a specific class field.

2. Parallel operations

With the addition of Lambda expressions to arrays operations, Java introduced a key concept into the language of internal iteration. Essentially as developers we’re used to use loop operations as one of the most basic programming idioms, right up there with if and else.

The introduction of Lambda expressions turned that paradigm around with the actual iteration over a collection over which a Lambda function is invoked is carried out by the core library.

You can think of this as an extension of iterators where the actual operation of extracting the next item from a collection on which to operate is carried out by an iterator. An exciting possibility opened by this design pattern is to enable operations carried out on long arrays such as sorting, filtering and mapping to be carried out in parallel by the framework. When dealing with server code that’s processing lengthy collections on a continuous basis, this can lead to major throughput improvements with relative work from your end.

Here’s the same snippet as above, but using the framework’s new parallel processing capabilities -

view source

print ?

1.ConcurrentMap<Person.Sex, List<Person>> byGender =

2.roster.parallelStream().collect(

3.Collectors.groupingByConcurrent(Person::getGender))

* It’s a fairly small change that’s required to make this algorithm run on multiple threads.

3. Java + JavaScript = ❤

Java 8 is looking to right one of its biggest historical wrongs – the ever growing distance between Java and JavaScript, one that has only increased in the past few years. With this new release, Java 8 is introducing a completely new JVM JavaScript engine – Nashorn. This engine makes unique use of some of the new features introduced in Java 7 such as invokeDynamic to provide JVM-level speed to JavaScript execution right there with the likes of V8 and SpiderMonkey.

This means that the next time you’re looking to integrate JS into your backend, instead of setting up a node.js instance, you can simply use the JVM to execute the code. The added bonus here is the ability to have seamless interoperability between your Java and JavaScript code in-process, without having to use various IPC/RPC methods to bridge the gap.

4. New date / time APIs

The complexity of the current native Java library API has been a cause of pain for Java developers for many years. Joda time has been filling this vacuum for years now, and with Java 8. An immediate question that arose early on was why didn’t Java 8 adopt Joda as its native time framework. Due to what was perceived as a design flaw in Joda, Java 8 implemented its own new date / time API from scratch. The good news is that unlike Calendar.getInstance(), the new APIs were designed with simplicity in mind, and clear operations to operate on manipulated values in both human readable and machine time formats.

5. Concurrent accumulators

One of the most common scenarios in concurrent programming is updating of numeric counters accessed by multiple threads. There have been many idioms to do this over the years, starting from synchronized blocks (which introduce a high level of contention), to read/write locks to AtomicInteger(s). While the last ones are more efficient, as they rely directly on processor CAS instructions, they require a higher degree of familiarity to implement the required semantics correctly.

With Java 8 this problem is solved at the framework level with new concurrent accumulator classes that enable you to very efficiently increase / decrease the value of a counter in a thread safe manner. This is really a case where it’s not a question of taste, or preference – using these new classes in your code is really a no-brainer.

Are there any other language features you think every developers should know about? Add them in the comments section.

Loading JDBC drivers

2014-01-12T19:17:00.000+05:30

Loading JDBC drivers

I split these examples into two specific categories which are good and dumb.


class dr1
{
    public static void main(String args[]) throws Exception
    {
        Class.forName("oracle.jdbc.driver.OracleDriver");
    }
}


class dr2
{
    public static void main(String args[]) throws Exception
    {
        // Choosing the driver at runtime
        Class.forName(args[0]);
    }
}


class dr3
{
    public static void main(String args[]) throws Exception
    {
        // Choosing the driver at runtime by a temporary
        // property
        Class.forName(System.getProperty("my.driver"));
    }
}

For executing this, you should write

java -Dmy.driver=oracle.jdbc.driver.OracleDriver dr3

The -D option is followed by the property name (without space) and =followed by the driver class. Don't forget the class name. It is damn important!

Note: The second, third and fourth ways have a common problem. Here if we aren't decisive about which driver to use and give it at runtime we need to change the URL (to connect to the database) too. Because, different drivers have different urls. So, there must be some conditional logic written which connects to the database via appropriate URL corresponding to the given class name. This becomes a bit messy. Isn't it?


class dr4
{
    public static void main(String args[])
    {
        // Choosing the driver at runtime by a permanent
        // property
        System.out.println("Driver loaded "+System.getProperty("jdbc.drivers"));
    }
}

Well, where is the code? I'll explain, everything lies in executing the program. You should execute this in this way.

java -Djdbc.drivers=oracle.jdbc.driver.OracleDriver dr4

Now, this loads the driver. The jdbc.drivers is an environment property of Java that corresponds to the JDBC drivers. The default value for this property is null. While executing, you are changing its value to the driver class name.

3 Dumb ways


class dr5
{
    public static void main(String args[])
    {
        // Creating an object for the driver class
        new oracle.jdbc.driver.OracleDriver();
    }
}

I call this dumb because, we are creating an object for this class which is absolutely unnecessary. Here is a simple question to you

Why create an object for a class when you are not going to use it? If you want to load the static block of the class? Isn't it enough to load the class into the memory using Class.forName() instead of creating an object for it?


class dr6
{
    public static void main(String args[]) throws Exception
    {
        // Using the registerDriver
        DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
    }
}

This way is double-dumb because you are loading the driver twice. Yes, thestatic block of the oracle.jdbc.driver.OracleDriver already contains a call to the registerDriver(). The statement, new oracle.jdbc.driver.OracleDriver(); loads it into memory (therefore, static block is executed) and creates an object for the driver class and then register the driver.


class dr7 extends oracle.jdbc.driver.OracleDriver
{
    public static void main(String args[])
    {
        System.out.println("Driver is loaded.");
    }
}

Simple Chat Application

2013-08-25T09:31:00.003+05:30

SIMPLE CHAT APPLICATION
1.Download this file compile and run and keep the command prompt open.....
This is the server code....

import java.io.*;
import java.net.*;
class VikramServer
{
public static void main (String args[]) throws Exception
{
try
{
String CStr="";
String UStr="";
System.out.println("********************* Server**********************");
ServerSocket SS = new ServerSocket(8888);
Socket OS = SS.accept();
DataInputStream Cinp =new DataInputStream(OS.getInputStream());
DataInputStream Uinp =new DataInputStream(System.in);
PrintStream PS = new PrintStream(OS.getOutputStream());
while(true)
{

CStr=Cinp.readLine();
System.out.println("Client : " +CStr);
if(CStr.equals("exit"))
break;
System.out.print("Server : ");
UStr=Uinp.readLine();
PS.println(UStr);

}
}catch(Exception e){System.err.println(e);};

}
}

2.Download this file compile and run and keep the command prompt open.....

This is the Client code ....

import java.io.*;
import java.net.*;
class VikramClient
{
public static void main(String args[]) throws Exception
{
try
{
String Schat="";
String Sstr="";
Socket SC = new Socket("localhost",8888);
DataInputStream Uinp =new DataInputStream(System.in);
DataInputStream Sinp =new DataInputStream(SC.getInputStream());
PrintStream PS = new PrintStream(SC.getOutputStream());
System.out.println("********************* Client**********************");
while(true)
{
System.out.print("Client : ");
Schat=Uinp.readLine();
if(Schat.equals("exit"))
break;
PS.println(Schat);
Sstr=Sinp.readLine();
System.out.println("Server : "+Sstr);
}
}catch(Exception e){System.err.println(e);};
}
}

Predict the Output !!!!!

2013-07-11T22:38:00.001+05:30

Public class Vikram
{
public static void main(String[] args)
{
http://vikram-programmingwithjava.blogspot.in/
System.out.println("Why is the URL allowed above?");
}
}
Will the Program Compile ???
If Yes what would be the Output and will http://vikram-programmingwithjava.blogspot.in/ be displayed in screen ?
If No what is the error in the program ???
Post your answers below.........

Program to find maximum and minimum number for a n*n matrix

2013-03-28T08:53:00.001+05:30

import java.io.*;
class test
{
public static void main(String[] asd)throws IOException
{
BufferedReader obj=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter the values of Rows and Columns of Matrix.");
String num=obj.readLine();
int r=Integer.parseInt(num);
num=obj.readLine();
int c=Integer.parseInt(num);
int m[][]= new int[r][c];
int max=0, min=0;
System.out.println("Enter the values of the matrix not more then "+(r*c)+".");
for(int i=0;i<r;i++)
for(int j=0;j<c;j++)
{
num=obj.readLine();
m[i][j]=Integer.parseInt(num);
}
System.out.println("Original matrix::");
for(int i=0;i<r;i++)
{
for(int j=0;j<c;j++)
{
System.out.print(m[i][j]+" ");
}
System.out.println();
}
// MAXIMUM element of the matrix max=m[0][0];
for(int i=0;i<r;i++)
{
for(int j=0;j<c;j++)
{
if(m[i][j]>max) max=m[i][j];
}
}
System.out.println("Maximum of the matrix is "+max+".");
//MINIMUM element of the matrix min=m[0][0];
for(int i=0;i<r;i++)
{
for(int j=0;j<c;j++)
{
if(m[i][j]<min) min=m[i][j];
}
}
System.out.println("Minimum of the matrix is "+min+".");
}
}

Four different ways to create an object in java

2013-03-27T18:21:00.001+05:30

1. Using new keyword
This is the most common way to create an object in java. I read somewhere that almost 99% of objects are created in this way.
MyObject object = new MyObject();
2. Using Class.forName()
If we know the name of the class & if it has a public default constructor we can create an object in this way.
MyObject object = (MyObject) Class.forName("subin.rnd.MyObject").newInstance();
3. Using clone()
The clone() can be used to create a copy of an existing object.
MyObject anotherObject = new MyObject();
MyObject object = anotherObject.clone();
4. Using object deserialization
Object deserialization is nothing but creating an object from its serialized form.
ObjectInputStream inStream = new ObjectInputStream(anInputStream );
MyObject object = (MyObject) inStream.readObject();

How To Create A War File In Netbeans

2013-03-19T09:29:00.005+05:30

Right click on your project name in the Explorer
Select Properties
In the Build | Packaging section, check "Compress War file" option.
Select file/folder and select your project then u can see war file in dist folder

Login with Swings

2013-02-01T18:04:00.000+05:30

Create a Login form and Index form with netbeans ide and inside Login form you can put two labels Name and password with a jTextField1 and jPasswordField1 and two buttons Submit and Cancel

Login

Submit
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
String s=jTextField1.getText();
String s1=jPasswordField1.getText();
Index i=new Index();
if(s.equals("Vikram")&&s1.equals("vikram"))
{
i.setVisible(true);
}
else if(!"Vicky".equals(s))
{
JOptionPane.showMessageDialog(this,"User Name Is Incorrect");
}
else
{

JOptionPane.showMessageDialog(this,"Password Is Incorrect");
}

}

Cancel

private void jButton2ActionPerformed(java.awt.event.ActionEvent evt)

{

System.exit(0);

}

Index

Date can be set to the textfield using the below code :

private void formWindowActivated(java.awt.event.WindowEvent evt)

{

Date d=new Date();

SimpleDateFormat da=new SimpleDateFormat("dd/MM/yyyy");

jTextField1.setText(da.format(d));

SimpleDateFormat vi=new SimpleDateFormat("hh:mm:ss");

jTextField2.setText(vi.format(d));

}

Jsp connection with mysql database

2013-02-01T17:47:00.002+05:30

Create a folder named user inside your web server (Tomcat) C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps and inside the user create WEB-INF and META-INF so that you can create a file inside META-INF named Content.xml and you need to create a empty folder WEB-INF and you can create and place the file test.jsp inside C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\user

Content.xml
<?xml version="1.0" encoding="UTF-8"?>
<Context antiJARLocking="true" path="/user"/>

test.jsp
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">

<%@ page import="java.sql.*" %>
<%@ page import="java.io.*" %>

<html>
<head>
<title>Connection with mysql database</title>
</head>
<body>
<h1>Connection status </h1>

<%
String connectionURL = "jdbc:mysql://localhost:3306/usermaster";
Connection connection = null;
ResultSet rst=null;
Statement st=null;

try
{
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(connectionURL, "root", "a");
st = connection.createStatement();
}
catch(Exception e)
{
System.out.println(e.getMessage());
}
if(request.getParameter("action") != null)
{
String un=request.getParameter("un");
String pw=request.getParameter("pwd");
rst=st.executeQuery("select * from login");
%>

<h2>Login/h2>
<table border="1" cellspacing="0" cellpadding="0">
<tr>

<td><b>User name</b></td>
<td><b>Password</b></td>
</tr>
<%

while(rst.next()){
%>
<tr>

<td><%=rst.getString("un")%></td>
<td> <%=rst.getString("pwd")%></td>
</tr>

<%

rst.close();
st.close();
connection.close();

%>
</table>
</body>
</html>
Please provide feedback readers.
Thank you
Vikram.S

EMBED APPLETS IN HTML

2012-10-31T18:23:00.000+05:30

When you put an applet on your page you will need to save the applet on your server as well as the HTML page the applet is embedded in. When the page is loaded by a visitor the applet will be loaded and inserted on the page where you embedded it.

Applets have the file extension "class". An example would be "myapplet.class". Some applets consist of more than just one class file, and often other files need to be present for the applet to run (such as JPG or GIF images used by the applet). Make sure to check the documentation for the applet to see if you have all files for it to run.
Before embedding an applet on your page you need to upload the required files to your server.

Below is a short example showing how simple it is to embed an applet on a page.

<Html>
<Head>
<Title>Java Example</Title>
</Head>

<Body>
This is my page<br>
Below you see an applet<br>
<br>
<Applet Code="MyApplet.class" width=200 Height=100>
</Applet>
</Body>
</Html> 

Two HTML tags are relevant according to applets: <Applet> and <Param>.

The <Applet> tag embeds the applet in your HTML page.
The <Param> tag is used to enter parameters for the applet.

The following attributes can be set for the <Applet> tag:

Attribute	Explanation	Example
Code	Name of class file	Code="myapplet.class"
Width=n	n=Width of applet	Width=200
Height=n	n=Height of applet	Height=100
Codebase	Library where the applet is stored. If the applet is in same directory as your page this can be omitted.	Codebase="applets/"
Alt="Text"	Text that will be shown in browsers where the ability to show applets has been turned off.	alt="Menu Applet"
Name=Name	Assigning a name to an applet can be used when applets should communicate with each other.	Name="starter"
Align= Left Right Top Texttop Middle Absmiddle Baseline Bottom Absbottom	Justifies the applet according to the text and images surrounding it.	Align=Right
Vspace=n	Space over and under the applet.	Vspace=20
Hspace=n	Space to the left and right of applet.	Hspace=40

The <Param> tag has the general syntax:

<Param Name=NameOfParameter Value="ValueOfParameter"> 

Each applet has different parameters that should be set.
Typical parameters for an applet would be:

color used by the applet

font and font size to be used on text in the applet

name of an image file to be inserted in the applet

Top 8 Java People You Should Know

2012-10-16T16:20:00.003+05:30

8. Tomcat & Ant Founder

James Duncan Davidson, while he was software engineer at Sun Microsystems (1997–2001), created Tomcat Java-based web server, still widely use in most of the Java web projects, and also Ant build tool, which uses XML to describe the build process and its dependencies, which is still the de facto standard for building Java-based Web applications.

Related Links

7. Test Driven Development & JUnit Founder

Kent Beck, creator of the Extreme Programming and Test Driven Development software development methodologies. Furthermore, he and Erich Gamma created JUnit, a simple testing framework, which turn into the de facto standard for testing Java-based Web applications. The combine of JUnit and Test Driven Development makes a big changed on the way of coding Java, which causes many Java developers are not willing to follow it.

Related Links

News & Interviews

Kent Beck Books

6. Java Collections Framework

Joshua Bloch, led the design and implementation of numerous Java platform features, including JDK 5.0 language enhancements and the award-winning Java Collections Framework. In June 2004 he left Sun and became Chief Java Architect at Google. Furthermore, he won the prestigious Jolt Award from Software Development Magazine for his book, “Effective Java”, which is arguably a must read Java’s book.

Related Links

News & Interviews

Joshua Bloch Books

5. JBoss Founder

Marc Fleury, who founded JBoss in 2001, an open-source Java application server, arguably the de facto standard for deploying Java-based Web applications. Later he sold the JBoss to RedHat, and joined RedHat to continue support on the JBoss development. On 9 February 2007, he decided to leave Red Hat to pursue other personal interests, such as teaching, research in biology, music and his family.

Related Links

News & Interviews

4. Struts Founder

Craig Mcclanahan, creator of Struts, a popular open source MVC framework for building Java-based web applications, which is arguably that every Java developer know how to code Struts. With the huge success of Struts in early day, it’s widely implemented in every single of the old Java web application project.

Related Links

News & Interviews

3. Spring Founder

Rod Johnson, is the founder of the Spring Framework, an open source application framework for Java, Creator of Spring, CEO at SpringSource. Furthermore, Rod’s best-selling Expert One-on-One J2EE Design and Development (2002) was one of the most influential books ever published on J2EE.

Related Links

News & Interviews

Rod Johnson Books

2. Hibernate Founder

Gavin King, is the founder of the Hibernate project, a popular object/relational persistence solution for Java, and the creator of Seam, an application framework for Java EE 5. Furthermore, he contributed heavily to the design of EJB 3.0 and JPA.

Related Links

News & Interviews

Gavin King Books

1. Father of the Java programming language

James Gosling, generally credited as the inventor of the Java programming language in 1994. He created the original design of Java and implemented its original compiler and virtual machine. For this achievement he was elected to the United States National Academy of Engineering. On April 2, 2010, he left Sun Microsystems which had recently been acquired by the Oracle Corporation. Regarding why he left, Gosling wrote on his blog that “Just about anything I could say that would be accurate and honest would do more harm than good.”

Related Links

News & Interviews

Note

Oracle 11g Release 2 Installation Steps

2012-10-02T12:10:00.002+05:30

The Oracle Database 11g Release 2 files are broken down into two zip files on the Oracle site. That means you need to download both files, and then expand them into an installation directory. I called my installation directory C:\OracleInstall, but you can call it whatever works for you. Here’s a screen shot of the directory after expanding both compressed files (done with WinZip 15).

You should notice that the two expanded compressed files put everything into a database directory (or folder). Within the installation folder (C:\OracleInstall\database), you double click on the oui icon to launch (start) the Oracle Universal Installer. It’ll open a command prompt that may dwell on the screen for a few seconds up to maybe fifteen seconds.

It’s a good idea to provide an email address for security updates no matter what. You can uncheck the box if you don’t want updates via Oracle Support Services. Click the Next button to continue.

Most developers want to Create and configure a database. If that’s your desire, leave the default radio button checked. Click the Next button to continue.

Most developers install their test instance on a desktop or laptop. If that’s your desire, leave the defaultDesktop Class radio button checked. Click the Next button to continue.

These are default settings and generally the easiest to use. I’d suggest you change the Character Set drop down to Unicode. Then, enter a password twice. Oracle requires that you use at least one capital letter and one number in a 6 character or more long password. Click the Next button to continue.

The next screen is a progress bar that checks for prerequisites. You shouldn’t have to do anything here because it automatically advances you to the next dialog screen. This generally takes less than a minute to run but can take two or so. If you’re much beyond 3 minutes there may be a resource problem with your Windows PC or virtual machine.

This shows you all the selected values for the installation. Unless you want to abort the installation, click the Finish button to proceed.

This screen is the main progress bar, and you’ll be here somewhere between 5 and 10 minutes. The downside is that there are some dialogs that will popup during this phase and you need to authorize them, so it’s a bad time to take a break.

The first popup screen requires you to authorize the Java runtime to call home. You should click the Allow Access button to proceed.

When the progress bar starts configuring the instance, failures can occur. The first may occur during the network configuration, which typically happens if you didn’t preconfigure the hosts file. You don’t need to do anything but watch here unless the installer triggers an error.

The following progress bar is launched by the Oracle Database Configuration Assistant. It typically runs without a problem. You don’t need to do anything but watch here unless the installer triggers an error. This takes a few minutes, and unfortunately requires you to stick aroung to again authorize Java.

The second popup screen requires you to authorize the Java runtime to call home. You should click theAllow Access button to proceed.

The third and last popup screen asks you to whether you want to open other scheme. Generally, you should click the OK button to proceed.

The next dialog shows you that the network and database instances are configured. It’s also running the OEM (Oracle Enterprise Manager) installation. You can wait here but it won’t be a long wait.

This is the last dialog and says you’ve installed Oracle Database 11g Release 2 successfully. You can theClose button to complete the installation.

Connecting Java and MySQL

2012-09-05T19:56:00.001+05:30

As you all know Java is one of the best programming languages around and MySQL is the world’s most popular open source database. Often these are used to build business applications. There arises the need to connect both of these technologies. But for a newbie like me it is quite a daunting task to make them talk to each other. So, I am putting forward a tutorial showing how to accomplish the task.

I am assuming that the reader have installed both Java and MySQL.

First of all we need MySQL Connector/J driver. It is the official JDBC driver for MySQL. Which can be downloaded from http://dev.mysql.com/downloads/connector/j/ .Moreover I have enclosed the driver used for this tutorial.

It was the easy part. Now the most confusing part if you don’t know how to set classpath. Classpath can be set in more than one way. I shall use the method which I prefer the most.

The file name of the MySQL Connector/J driver I have downloaded is

mysql-connector-java-5.1.11-bin.jar

I have kept this file in C:\Program Files\Java\jdk1.6.0_12\lib in my system. You can place it anywhere you like.

JAR file (or Java ARchive) collection of many files into one. Java developers generally use .jar files to distribute Java applications or libraries, in the form of classes and associated metadata and resources. In this case mysql-connector-java-5.1.11-bin.jar file contains all the classes required for Java, MySQL connection.

Now I shall set the classpath so that our program can use this library to connect the MySQL database.

Click Start or the Windows icon in the bottom left corner of your screen. Then Select Computer, Properties.

Now Select Advanced System Settings

Select Environment Variable in the System Properties Window

Choose ClassPath from the System Variable Pane and click Edit Button.

Enter the Path of mysql-connector-java-5.1.11-bin.jar file after putting a semicolon in case there are previous settings. In most cases there you would find some. Click Ok couples of time. That’s all. You have set the classpath. In some instances you might have to restart your system.
Now we shall write the code to connect MySQL database.

import java.sql.*;

public class TestConnection{
public static void main(String[] args) {
System.out.println("MySQL Connect Example.");
Connection conn = null;
String url = "jdbc:mysql://localhost:3306/";
String dbName = "test";
String driver = "com.mysql.jdbc.Driver";
String userName = "root";
String password = "";
try {
Class.forName(driver).newInstance();
conn = DriverManager.getConnection(url+dbName,userName,password);
System.out.println("Connected to the database");
conn.close();
System.out.println("Disconnected from database");
} catch (Exception e) {
e.printStackTrace();
}
}
}
mysql-connector-java-5.1.11-bin.jar is the best as i am connnected with it with the latest version am facing some issues will post after correcting them......
Thank you guys............Stay tuned !!!!!!!!

Send HTTP request & fetching data using Java

2012-09-02T08:26:00.000+05:30

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.net.URL;

public class Main {

    public static void main(String[] args)  {

        try {

            URL my_url = new URL("http://www.vikram-programmingwithjava.blogspot.in");

            BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));

            String strTemp = "";

            while(null != (strTemp = br.readLine())){

            System.out.println(strTemp);

        }

        } catch (Exception ex) {

            ex.printStackTrace();

        }

    }

}

Connecting to Oracle using Java JDBC

2012-09-02T08:01:00.003+05:30

import java.util.*;
import java.sql.*;

public class OracleJdbcTest

{

String driverClass = "oracle.jdbc.driver.OracleDriver";

Connection con;

public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException

{

Properties props = new Properties();

props.load(fs);

String url = props.getProperty("db.url");

String userName = props.getProperty("db.user");

String password = props.getProperty("db.password");

Class.forName(driverClass);

con=DriverManager.getConnection(url, userName, password);

}

public void fetch() throws SQLException, IOException

{

PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");

ResultSet rs = ps.executeQuery();

while (rs.next())

{

// YOUR LOGIC

}

rs.close();

ps.close();

}

public static void main(String[] args)

{

OracleJdbcTest test = new OracleJdbcTest();

test.init();

test.fetch();

}

Java and My Sql datatypes

2012-08-26T16:24:00.000+05:30

The following table represent the default Java mapping for various common MySQL data types:

MySQL Type	Java Type
CHAR	String
VARCHAR	String
LONGVARCHAR	String
NUMERIC	java.math.BigDecimal
DECIMAL	java.math.BigDecimal
BIT	boolean
TINYINT	byte
SMALLINT	short
INTEGER	int
BIGINT	long
REAL	float
FLOAT	double
DOUBLE	double
BINARY	byte []
VARBINARY	byte []
LONGVARBINARY	byte []
DATE	java.sql.Date
TIME	java.sql.Time
TIMESTAMP	java.sql.Tiimestamp

CHAR, VARCHAR and LONGVARCHAR
MySQL data types CHAR, VARCHAR, LONGVARCHAR are closely related. CHAR represents a small, fixed-length character string, VARCHAR represents a small, variable-length character string, and LONGVARCHAR represents a large, variable-length character string. There is no need for Java programmer to distinguish these three MySQL data types. These can be expressed identically in Java. These data types could be mapped in Java to either String or char[]. But String seemed more appropriate type for normal use. Java String class provide a method to convert a String into char[] and a constructor for converting a char[] into a String.

The method ResultSet.getString allocates and returns a new String. It is suitable for retrieving data from CHAR, VARCHAR and LONGVARCHAR fields. This is suitable for retrieving normal data, but LONGVARCHAR MySQL type can be used to store multi-megabyte strings. So that Java programmers needs a way to retrieve the LONGVARCHAR value in chunks. To handle this situation, ResultSet interface have two methods for allowing programmers to retrieve aLONGVARCHAR value as a Java input stream from which they can subsequently read data in whatever size chunks they prefer. These methods are getAsciiStream andgetCharacterStream, which deliver the data stored in a LONGVARCHAR column as a stream of ASCII or Unicode characters.

NUMERIC and DECIMALThe NUMERIC and DECIMAL MySQL data types are very similar. They both represent fixed point numbers where absolute precision is required. The most convenient Java mapping for theseMySQL data type is java.math.BigDecimal. This Java type provides math operations to allowBigDecimal types to be added, subtracted, multiplied, and divided with other BigDecimaltypes, with integer types, and with floating point types.

We also allow access to these MySQL types as simple Strings and char []. Thus, the Java programmers can use the getString() to retrieve the NUMERICAL and DECIMAL results.

BINARY, VARBINARY and LONGVARBINARY
These MySQL data types are closely related. BINARY represents a small, fixed-length binary value, VARBINARY represents a small, variable-length binary value and LONGVARBINARYrepresents a large, variable-length binary value. For Java programers there is no need to distinguish among these data types and they can all be expressed identically as byte arrays in Java. It is possible to read and write SQL statements correctly without knowing the exactBINARY data type. The ResultSet.getBytes method is used for retrieving the DECIMAL andNUMERICAL values. Same as LONGVARCHAR type, LONGVARBINARY type can also be used to return multi-megabyte data values then the method getBinaryStream is recommended.

BITThe MySQL type BIT represents a single bit value that can be 'zero' or 'one'. And this MySQLtype can be mapped directly to the Java boolean type.

TINYINT, SMALLINT, INTEGER and BIGINT
The MySQL TINYINT type represents an 8-bit integer value between 0 and 255 that may be signed or unsigned. SMALLINT type represents a 16-bit signed integer value between -32768 and 32767. INTEGER type represents a 32-bit signed integer value between -2147483648 and 2147483647. BIGINT type represents an 64-bit signed integer value between -9223372036854775808 and 9223372036854775807. These MySQL TINYINT, SMALLINT, INTEGER, and BIGINT types can be mapped to Java's byte, short, int and long data types respectively.

REAL, FLOAT and DOUBLE
The MySQL REAL represents a "single precision" floating point number that supports seven digits of mantissa and the FLOAT and DOUBLE type represents a "double precision" floating point number that supports 15 digits of mantissa. The recommended Java mapping for REALtype to Java float and FLOAT, DOUBLE type to Java double.

DATE, TIME and TIMESTAMP
These three MySQL types are related to time. The DATE type represents a date consisting of day, month, and year, the TIME type represents a time consisting of hours, minutes, and seconds and the TIMESTAMP type represents DATE plus TIME plus a nanosecond field. The standard Java class java.util.Date that provides date and time information but does not match any of these three MySQL date/time types exactly, because it has DATE and TIME information but no nanoseconds.
That's why we define three subclasses of java.util.Date. These are:
- java.sql.Date for SQL DATE information.
- java.sql.Timestamp for SQL TIMESTAMP information.

Java with MySql

2012-08-26T16:12:00.002+05:30

1. Java Database Connectivity (JDBC)

The interface for accessing relational databases from Java is JDBC. Via JDBC you maintain the databases connection, issue database queries and updates and receive the results.

JDBC is an interface independently of any database. For each database you require the database specific implementation of the JDBC driver.

2. Introduction to MySQL

To learn to install and use MySQL please see MySQL - Tutorial.

The following will assume that you have successfully installed MySQL and know how to access MySQL via the command line.

3. MySQL JDBC driver

To connect to MySQL from Java you have to use the JDBC driver from MySQL. The MySQL JDBC driver is called "MySQL Connector/J". You should be able to find the latest MySQL JDBC driver on this pagehttp://dev.mysql.com/downloads/connector/j .

The download contains a jar file which we require later.

4. Create example database

Start the MySQL command line client and paste the following SQL script into it to create a sample database which we can use as an example.

create database feedback;
use feedback;
CREATE USER sqluser IDENTIFIED BY 'sqluserpw'; 
grant usage on *.* to sqluser@localhost identified by 'sqluserpw'; 
grant all privileges on feedback.* to sqluser@localhost;

CREATE TABLE COMMENTS (id INT NOT NULL AUTO_INCREMENT, 
    MYUSER VARCHAR(30) NOT NULL,
    EMAIL VARCHAR(30), 
    WEBPAGE VARCHAR(100) NOT NULL, 
    DATUM DATE NOT NULL, 
    SUMMERY VARCHAR(40) NOT NULL,
    COMMENTS VARCHAR(400) NOT NULL,
    PRIMARY KEY (ID));

INSERT INTO COMMENTS values (default, 'lars', 'myemail@gmail.com','http://www.vogella.com', '2009-09-14 10:33:11', 'Summery','My first comment');

5. Java JDBC

Create a Java project and a package "de.vogella.mysql.first".

Create a folder "lib" and copy the JDBC driver into this folder. Add the JDBC driver to your classpath. SeeAdding jars to the classpath for details.

Create the following class to connect to the MySQL database and perform queries, inserts and deletes. It also prints the metadata (table name, column names) of a query result.

package de.vogella.mysql.first;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;

public class MySQLAccess {
  private Connection connect = null;
  private Statement statement = null;
  private PreparedStatement preparedStatement = null;
  private ResultSet resultSet = null;

  public void readDataBase() throws Exception {
    try {
      // This will load the MySQL driver, each DB has its own driver
      Class.forName("com.mysql.jdbc.Driver");
      // Setup the connection with the DB
      connect = DriverManager
          .getConnection("jdbc:mysql://localhost/feedback?"
              + "user=sqluser&password=sqluserpw");

      // Statements allow to issue SQL queries to the database
      statement = connect.createStatement();
      // Result set get the result of the SQL query
      resultSet = statement
          .executeQuery("select * from FEEDBACK.COMMENTS");
      writeResultSet(resultSet);

      // PreparedStatements can use variables and are more efficient
      preparedStatement = connect
          .prepareStatement("insert into  FEEDBACK.COMMENTS values (default, ?, ?, ?, ? , ?, ?)");
      // "myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
      // Parameters start with 1
      preparedStatement.setString(1, "Test");
      preparedStatement.setString(2, "TestEmail");
      preparedStatement.setString(3, "TestWebpage");
      preparedStatement.setDate(4, new java.sql.Date(2009, 12, 11));
      preparedStatement.setString(5, "TestSummary");
      preparedStatement.setString(6, "TestComment");
      preparedStatement.executeUpdate();

      preparedStatement = connect
          .prepareStatement("SELECT myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
      resultSet = preparedStatement.executeQuery();
      writeResultSet(resultSet);

      // Remove again the insert comment
      preparedStatement = connect
      .prepareStatement("delete from FEEDBACK.COMMENTS where myuser= ? ; ");
      preparedStatement.setString(1, "Test");
      preparedStatement.executeUpdate();
      
      resultSet = statement
      .executeQuery("select * from FEEDBACK.COMMENTS");
      writeMetaData(resultSet);
      
    } catch (Exception e) {
      throw e;
    } finally {
      close();
    }

  }

  private void writeMetaData(ResultSet resultSet) throws SQLException {
    //   Now get some metadata from the database
    // Result set get the result of the SQL query
    
    System.out.println("The columns in the table are: ");
    
    System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
    for  (int i = 1; i<= resultSet.getMetaData().getColumnCount(); i++){
      System.out.println("Column " +i  + " "+ resultSet.getMetaData().getColumnName(i));
    }
  }

  private void writeResultSet(ResultSet resultSet) throws SQLException {
    // ResultSet is initially before the first data set
    while (resultSet.next()) {
      // It is possible to get the columns via name
      // also possible to get the columns via the column number
      // which starts at 1
      // e.g. resultSet.getSTring(2);
      String user = resultSet.getString("myuser");
      String website = resultSet.getString("webpage");
      String summery = resultSet.getString("summery");
      Date date = resultSet.getDate("datum");
      String comment = resultSet.getString("comments");
      System.out.println("User: " + user);
      System.out.println("Website: " + website);
      System.out.println("Summery: " + summery);
      System.out.println("Date: " + date);
      System.out.println("Comment: " + comment);
    }
  }

  // You need to close the resultSet
  private void close() {
    try {
      if (resultSet != null) {
        resultSet.close();
      }

      if (statement != null) {
        statement.close();
      }

      if (connect != null) {
        connect.close();
      }
    } catch (Exception e) {

    }
  }

}

Create the following main program to test your class.

package de.vogella.mysql.first.test;

import de.vogella.mysql.first.MySQLAccess;

public class Main {
  public static void main(String[] args) throws Exception {
    MySQLAccess dao = new MySQLAccess();
    dao.readDataBase();
  }


}

JDBC – Insert A Record

2012-08-18T11:53:00.003+05:30

Here’s an example to show you how to insert a record into table via JDBC statement. To issue a insert statement, calls theStatement.executeUpdate() method like this :

Statement statement = dbConnection.createStatement();
// execute the insert SQL stetement
statement.executeUpdate(insertTableSQL);

Full example…

package com.mkyong.jdbc;
 
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
 
public class JDBCStatementInsertExample {
 
 private static final String DB_DRIVER = "oracle.jdbc.driver.OracleDriver";
 private static final String DB_CONNECTION = "jdbc:oracle:thin:@localhost:1521:MKYONG";
 private static final String DB_USER = "user";
 private static final String DB_PASSWORD = "password";
 private static final DateFormat dateFormat = new SimpleDateFormat(
   "yyyy/MM/dd HH:mm:ss");
 
 public static void main(String[] argv) {
 
  try {
 
   insertRecordIntoDbUserTable();
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  }
 
 }
 
 private static void insertRecordIntoDbUserTable() throws SQLException {
 
  Connection dbConnection = null;
  Statement statement = null;
 
  String insertTableSQL = "INSERT INTO DBUSER"
    + "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) " + "VALUES"
    + "(1,'mkyong','system', " + "to_date('"
    + getCurrentTimeStamp() + "', 'yyyy/mm/dd hh24:mi:ss'))";
 
  try {
   dbConnection = getDBConnection();
   statement = dbConnection.createStatement();
 
   System.out.println(insertTableSQL);
 
   // execute insert SQL stetement
   statement.executeUpdate(insertTableSQL);
 
   System.out.println("Record is inserted into DBUSER table!");
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  } finally {
 
   if (statement != null) {
    statement.close();
   }
 
   if (dbConnection != null) {
    dbConnection.close();
   }
 
  }
 
 }
 
 private static Connection getDBConnection() {
 
  Connection dbConnection = null;
 
  try {
 
   Class.forName(DB_DRIVER);
 
  } catch (ClassNotFoundException e) {
 
   System.out.println(e.getMessage());
 
  }
 
  try {
 
   dbConnection = DriverManager.getConnection(
                               DB_CONNECTION, DB_USER,DB_PASSWORD);
   return dbConnection;
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  }
 
  return dbConnection;
 
 }
 
 private static String getCurrentTimeStamp() {
 
  java.util.Date today = new java.util.Date();
  return dateFormat.format(today.getTime());
 
 }
 
}

Result

A record is inserted into a table named “DBUSER”.

INSERT INTO DBUSER(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) 
VALUES(1,'mkyong','system', to_date('2011/04/04 13:59:03', 'yyyy/mm/dd hh24:mi:ss'))
Record IS inserted INTO DBUSER TABLE!

JDBC - Create A Table

2012-08-18T11:51:00.000+05:30

JDBC Statement Example – Create A Table

Here’s an example to show you how to create a table in database via JDBC statement. To issue a create statement, calls the Statement.execute() method like this :

Statement statement = dbConnection.createStatement();
// execute create SQL stetement
statement.execute(createTableSQL);

Full example…

package com.mkyong.jdbc;
 
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
 
public class JDBCStatementCreateExample {
 
 private static final String DB_DRIVER = "oracle.jdbc.driver.OracleDriver";
 private static final String DB_CONNECTION = "jdbc:oracle:thin:@localhost:1521:MKYONG";
 private static final String DB_USER = "user";
 private static final String DB_PASSWORD = "password";
 
 public static void main(String[] argv) {
 
  try {
 
   createDbUserTable();
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  }
 
 }
 
 private static void createDbUserTable() throws SQLException {
 
  Connection dbConnection = null;
  Statement statement = null;
 
  String createTableSQL = "CREATE TABLE DBUSER("
    + "USER_ID NUMBER(5) NOT NULL, "
    + "USERNAME VARCHAR(20) NOT NULL, "
    + "CREATED_BY VARCHAR(20) NOT NULL, "
    + "CREATED_DATE DATE NOT NULL, " + "PRIMARY KEY (USER_ID) "
    + ")";
 
  try {
   dbConnection = getDBConnection();
   statement = dbConnection.createStatement();
 
   System.out.println(createTableSQL);
                        // execute the SQL stetement
   statement.execute(createTableSQL);
 
   System.out.println("Table \"dbuser\" is created!");
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  } finally {
 
   if (statement != null) {
    statement.close();
   }
 
   if (dbConnection != null) {
    dbConnection.close();
   }
 
  }
 
 }
 
 private static Connection getDBConnection() {
 
  Connection dbConnection = null;
 
  try {
 
   Class.forName(DB_DRIVER);
 
  } catch (ClassNotFoundException e) {
 
   System.out.println(e.getMessage());
 
  }
 
  try {
 
   dbConnection = DriverManager.getConnection(
     DB_CONNECTION, DB_USER,DB_PASSWORD);
   return dbConnection;
 
  } catch (SQLException e) {
 
   System.out.println(e.getMessage());
 
  }
 
  return dbConnection;
 
 }
 
}

Result

Here’s the result.

CREATE TABLE DBUSER(
  USER_ID NUMBER(5) NOT NULL, 
  USERNAME VARCHAR(20) NOT NULL, 
  CREATED_BY VARCHAR(20) NOT NULL, 
  CREATED_DATE DATE NOT NULL, 
  PRIMARY KEY (USER_ID) 
)
TABLE "user" IS created!

2012-08-16T23:56:00.004+05:30

Connect To Oracle DB Via JDBC Driver

Here’s an example to show you how to connect to Oracle database via JDBC driver.

1. Download MySQL JDBC Driver

Get Oracle JDBC driver here – ojdbcxxx.jar

2. Java JDBC Connection Example

Code snippets to use JDBC to connect a Oracle database.

Class.forName("org.postgresql.Driver");
Connection connection = null;
connection = DriverManager.getConnection(
 "jdbc:oracle:thin:@localhost:1521:mkyong","username","password");
connection.close();

See a complete example below :
File : OracleJDBC.java

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
 
public class OracleJDBC {
 
 public static void main(String[] argv) {
 
  System.out.println("-------- Oracle JDBC Connection Testing ------");
 
  try {
 
   Class.forName("oracle.jdbc.driver.OracleDriver");
 
  } catch (ClassNotFoundException e) {
 
   System.out.println("Where is your Oracle JDBC Driver?");
   e.printStackTrace();
   return;
 
  }
 
  System.out.println("Oracle JDBC Driver Registered!");
 
  Connection connection = null;
 
  try {
 
   connection = DriverManager.getConnection(
     "jdbc:oracle:thin:@localhost:1521:mkyong", "username",
     "password");
 
  } catch (SQLException e) {
 
   System.out.println("Connection Failed! Check output console");
   e.printStackTrace();
   return;
 
  }
 
  if (connection != null) {
   System.out.println("You made it, take control your database now!");
  } else {
   System.out.println("Failed to make connection!");
  }
 }
 
}

2. Run It

Assume OracleJDBC.java is store in “C:\jdbc-test” folder, together with Oracle JDBC driver (ojdbc6.jar), then run following commands :

C:\jdbc-test>javac OracleJDBC.java
 
C:\jdbc-test>java -cp c:\jdbc-test\ojdbc6.jar;c:\jdbc-test OracleJDBC
-------- Oracle JDBC Connection Testing ------------
Oracle JDBC Driver Registered!
You made it, take control your database now!
 
C:\jdbc-test>

Done

2012-08-16T23:55:00.004+05:30

Connect To MySQL With JDBC Driver

Here’s an example to show you how to connect to MySQL database via JDBC driver.

1. Download MySQL JDBC Driver

Get a MySQL JDBC driver from here -MySQL JDBC Driver Download Here

2. Java JDBC Connection Example

Code snippets to use JDBC to connect a MySQL database.

  Class.forName("com.mysql.jdbc.Driver");
  Connection connection = null;
  connection = DriverManager.getConnection(
          "jdbc:mysql://hostname:port/dbname","username", "password");
  connection.close();

See a complete example below :
File : JDBCExample.java

package com.mkyong.common;
 
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
 
public class JDBCExample {
 
 public static void main(String[] argv) {
 
  System.out.println("-------- MySQL JDBC Connection Testing ------------");
 
  try {
 
   Class.forName("com.mysql.jdbc.Driver");
 
  } catch (ClassNotFoundException e) {
 
   System.out.println("Where is your MySQL JDBC Driver?");
   e.printStackTrace();
   return;
 
  }
 
  System.out.println("MySQL JDBC Driver Registered!");
  Connection connection = null;
 
  try {
   connection = DriverManager
     .getConnection("jdbc:mysql://localhost:3306/mkyongcom",
       "root", "password");
 
  } catch (SQLException e) {
   System.out.println("Connection Failed! Check output console");
   e.printStackTrace();
   return;
  }
 
  if (connection != null) {
   System.out.println("You made it, take control your database now!");
  } else {
   System.out.println("Failed to make connection!");
  }
 }
}

3. Run It

Assume JDBCExample.java is store in c:\test folder, together with MySQL JDBC driver

C:\test>java -cp c:\test\mysql-connector-java-5.1.8-bin.jar;c:\test JDBCExample
-------- MySQL JDBC Connection Testing ------------
MySQL JDBC Driver Registered!
You made it, take control your database now!
 
C:\test>

Android Button Example

2012-08-16T23:54:00.002+05:30

Android Button Example

In Android, just use “android.widget.Button” class to display a normal button.

In this tutorial, we show you how to display a normal button, add a click listener, when user click on the button, open an URL in your Android’s internet browser.

P.S This project is developed in Eclipse 3.7, and tested with Android 2.3.3.

Note
For more advance function, like image, please refer to this ImageButton example and also this ImageButton selector example.

1. Add Button

Open “res/layout/main.xml” file, add a button.

File : res/layout/main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
 
    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button - Go to mkyong.com" />
 
</LinearLayout>

2. Code Code

Attach a click listener to the button.

When user click on it, open mobile browser and display URL : http://www.mkyong.com.

File : MyAndroidAppActivity.java

package com.mkyong.android;
 
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
 
public class MyAndroidAppActivity extends Activity {
 
 Button button;
 
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 
  addListenerOnButton();
 
 }
 
 public void addListenerOnButton() {
 
  button = (Button) findViewById(R.id.button1);
 
  button.setOnClickListener(new OnClickListener() {
 
   @Override
   public void onClick(View arg0) {
 
     Intent browserIntent = 
                            new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.mkyong.com"));
       startActivity(browserIntent);
 
   }
 
  });
 
 }
 
}

3. Demo

Run the application.

1. Result, a normal button.

2. Click on the button, display URL in browser.

How To Make A Phone Call In Android

2012-08-12T10:54:00.002+05:30

How To Make A Phone Call In Android

In this tutorial, we show you how to make a phone call in Android,and monitor the phone call states viaPhoneStateListener.

P.S This project is developed in Eclipse 3.7, and tested with Android 2.3.3.

1 Android Layout Files

Simpel layout file, to display a button.

File : res/layout/main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
 
    <Button
        android:id="@+id/buttonCall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="call 0377778888" />
 
</LinearLayout>

2. Activity

Use below code snippet to make a phone call in Android.

 Intent callIntent = new Intent(Intent.ACTION_CALL);
 callIntent.setData(Uri.parse("tel:0377778888"));
 startActivity(callIntent);

File : MainActivity.java – When the button is call, make a phone to 0377778888.

package com.mkyong.android;
 
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
 
public class MainActivity extends Activity {
 
 private Button button;
 
 public void onCreate(Bundle savedInstanceState) {
 
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 
  button = (Button) findViewById(R.id.buttonCall);
 
  // add button listener
  button.setOnClickListener(new OnClickListener() {
 
   @Override
   public void onClick(View arg0) {
 
    Intent callIntent = new Intent(Intent.ACTION_CALL);
    callIntent.setData(Uri.parse("tel:0377778888"));
    startActivity(callIntent);
 
   }
 
  });
 
 }
 
}

3 Android Manifest

To make a phone call, Android need CALL_PHONE permission.

<uses-permission android:name="android.permission.CALL_PHONE" />

File : AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mkyong.android"
    android:versionCode="1"
    android:versionName="1.0" >
 
    <uses-sdk android:minSdkVersion="10" />
 
 <uses-permission android:name="android.permission.CALL_PHONE" />
 
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
 
        <activity
            android:label="@string/app_name"
            android:name=".MainActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
 
</manifest>

4. PhoneStateListener Example

Ok, now we update the above activity, to monitor the phone call states, when a phone call is ended, come back to the original activity (actually, it just restart the activity). Read comment, it should be self-explanatory.

Note
Run it and refer to the logcat console to understand how PhoneStateListener works.

File : MainActivity.java

package com.mkyong.android;
 
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
 
public class MainActivity extends Activity {
 
 final Context context = this;
 private Button button;
 
 public void onCreate(Bundle savedInstanceState) {
 
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 
  button = (Button) findViewById(R.id.buttonCall);
 
  // add PhoneStateListener
  PhoneCallListener phoneListener = new PhoneCallListener();
  TelephonyManager telephonyManager = (TelephonyManager) this
   .getSystemService(Context.TELEPHONY_SERVICE);
  telephonyManager.listen(phoneListener,PhoneStateListener.LISTEN_CALL_STATE);
 
  // add button listener
  button.setOnClickListener(new OnClickListener() {
 
   @Override
   public void onClick(View arg0) {
 
    Intent callIntent = new Intent(Intent.ACTION_CALL);
    callIntent.setData(Uri.parse("tel:0377778888"));
    startActivity(callIntent);
 
   }
 
  });
 
 }
 
 //monitor phone call activities
 private class PhoneCallListener extends PhoneStateListener {
 
  private boolean isPhoneCalling = false;
 
  String LOG_TAG = "LOGGING 123";
 
  @Override
  public void onCallStateChanged(int state, String incomingNumber) {
 
   if (TelephonyManager.CALL_STATE_RINGING == state) {
    // phone ringing
    Log.i(LOG_TAG, "RINGING, number: " + incomingNumber);
   }
 
   if (TelephonyManager.CALL_STATE_OFFHOOK == state) {
    // active
    Log.i(LOG_TAG, "OFFHOOK");
 
    isPhoneCalling = true;
   }
 
   if (TelephonyManager.CALL_STATE_IDLE == state) {
    // run when class initial and phone call ended, 
    // need detect flag from CALL_STATE_OFFHOOK
    Log.i(LOG_TAG, "IDLE");
 
    if (isPhoneCalling) {
 
     Log.i(LOG_TAG, "restart app");
 
     // restart app
     Intent i = getBaseContext().getPackageManager()
      .getLaunchIntentForPackage(
       getBaseContext().getPackageName());
     i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
     startActivity(i);
 
     isPhoneCalling = false;
    }
 
   }
  }
 }
 
}

Update Android Manifest file again, PhoneStateListener need READ_PHONE_STATE permission.

<uses-permission android:name="android.permission.READ_PHONE_STATE" />

File : AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mkyong.android"
    android:versionCode="1"
    android:versionName="1.0" >
 
    <uses-sdk android:minSdkVersion="10" />
 
    <uses-permission android:name="android.permission.CALL_PHONE" />
    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
 
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
 
        <activity
            android:label="@string/app_name"
            android:name=".MainActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
 
</manifest>

5. Demo

Activity started, just display a button.

When button is clicked, make a phone call to 0377778888.

When phone call is hang out or ended, restart the main activity.

Register variables

2012-08-12T10:51:00.002+05:30

Register variables are stored in the CPU registers. Its default value is a garbage value. Scope of a register
variable is local to the block in which it is defined. Lifetime is till control remains within the block in which the
register variable is defined. Variable stored in a CPU register can always be accessed faster than the one that is stored in memory. Therefore, if a variable is used at many places in a program, it is better to declare its storage class as register
Example:
register int x=5;
Variables for loop counters can be declared as register. Note that register keyword may be ignored by some
compilers.

Static variable

2012-08-12T10:50:00.000+05:30

A static variable is a special variable that is stored in the data segment unlike the default automatic variable that
is stored in stack. A static variable can be initialized by using keyword static before variable name.
Example:
static int a = 5;
A static variable behaves in a different manner depending upon whether it is a global variable or a local variable.
A static global variable is same as an ordinary global variable except that it cannot be accessed by other files in the same program / project even with the use of keyword extern. A static local variable is different from local variable. It is initialized only once no matter how many times that function in which it resides is called. It may be used as a count variable.
Example:
#include <stdio.h>
//program in file f1.c
void count(void) {
static int count1 = 0;
int count2 = 0;
count1++;
count2++;
printf("\nValue of count1 is %d, Value of count2 is %d", count1, count2);
}/
*Main function*/
int main(){
count();
count();
count();
return 0;
}
Output:
Value of count1 is 1, Value of count2 is 1
Value of count1 is 2, Value of count2 is 1
Value of count1 is 3, Value of count2 is 1