Applet Life Cycle in Java with Example

Applet in Java

Applet in Java is a special Java program that are primarily used in a internet programming.

Applet Life Cycle is very important to know in Java Applet Programming.

As we have already seen how to run program from command prompt, but there were no GUI.

To provide Graphical user interface(GUI) Java Applet is used.

Applet program runs on a web browser at client side. Applet program are used to make the web site more dynamic.

1 Life Cycle of Applet Stages

When the applet program is loaded is passes through several stages:

Born or initialization
Running
Idle  or stopped                                                                                                              
Dead or terminate

Born or initialization

Running

Idle or stopped

Dead or terminate

A Applet Born State

Also known as initialization state.

It is the first state of applet lifecycle.

Applet enters in a born/ initialization state when it is first loaded.

Applet moves in a born state when init() method of Applet class executes.

Applet initialization occurs once in a applet lifecycle.

Inside the init() method we initialize all the variables.

Syntax of init() method in Java Applet

public void init(){				
}

1 2	public void init(){ }

B Applet Running State

Applet enters in a running state from born state when a start() method of Applet class executes.

Running sates call automatically when the initialization phase completes.

Applet also comes in a running state from idle state when idle applet again get processor.

Running sates call automatically when the initialization phase completes.

Applet also comes in a running state from idle state when idle applet again get processor.

Syntax of start()

public void start(){				
}

1 2	public void start(){ }

C Applet Idle State

A running appletenters in a idle sate from running state when execution of start complete.

In a another words when we leave the page of running applet then automatically it enters in a idle sate from running state.

Applet moves in idle state when stop() method executes and it moves idle to running state when again start() calls.

Syntax of stop()

public void stop(){				
}

1 2	public void stop(){ }

D Applet Dead State

An applet is moved to dead state when we quit the web browser. When applet moves in a dead state it removed from memory.

The Applet will be terminate when destroy () method calls. In a applet lifecycle, applet terminates/destroys ones.

Syntax of destroy()

public void destroy(){				
}

1 2	public void destroy(){ }

E Applet Display State

The Display state executes immediately after when applet enters in a running state.

In this state we display the information on the output screen using paint() method.

public void paint(Graphics  g){						
}

1 2	public void paint(Graphics g){ }

2 Applet Life Cycle Program in Java Example

Lets see one program to demonstrate the life cycle of applet.

import java.applet.Applet;
import java.awt.Graphics;
/* 
<applet code="AppletLifeCycle.class" width="500" height="500"> 
</applet> 
 */
public class AppletLifeCycle extends Applet {
    String s;
    public void init() {
        s = "Welcome to Java Applet";
        System.out.println("Inside init method");
    }
    public void start() {
        System.out.println("Inside start method");
    }
    public void paint(Graphics g) {
        System.out.println("Inside paint method");
        g.drawString(s, 100, 100);
    }
    public void stop() {
        System.out.println("Inside stop method");
    }
    public void destroy() {
        System.out.println("Inside destroy method");
    }
}

import java.applet.Applet;

import java.awt.Graphics;

</applet>

public class AppletLifeCycle extends Applet {

String s;

public void init() {

s = "Welcome to Java Applet";

System.out.println("Inside init method");

}

public void start() {

System.out.println("Inside start method");

}

public void paint(Graphics g) {

System.out.println("Inside paint method");

g.drawString(s, 100, 100);

}

public void stop() {

System.out.println("Inside stop method");

}

public void destroy() {

System.out.println("Inside destroy method");

}

Life cycle methods are called and System.out.println() statement is written to check the execution.

On execution you will get following result.

Compile and Run the program

>javac AppletLifeCycle.java
>appletviewer AppletLifeCycle.java

Applet Life Cycle in Java Example — Fig: Java Applet Life Cycle Example

Output At Console

Inside init method
Inside start method
Inside paint method
Inside stop method
Inside destroy method

Inside init method

Inside start method

Inside paint method

Inside stop method

Inside destroy method

On running Applet It will print first 3 line from output.

On closing applet it will call stop and destroy method.

init() method can be used to initialize various values and objects that are going to use in program.

Similarly to release resource we can use destroy().

Example: Write a program to read file and show in java applet.

import java.applet.Applet;
import java.awt.Graphics;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;


/* 
<applet code="AppletLifeCycle.class" width="800" height="800"> 
</applet> 
 */
public class AppletLifeCycle extends Applet {

    File file;
    Scanner scanner;

    public void init() {
        sb = new StringBuffer();
        file = new File("D:\\test.txt");
        System.out.println("Inside init method: created StringBuffer and File Object");
    }

    public void start() {
        System.out.println("Inside start method");
    }
    public void paint(Graphics g) {
        System.out.println("Inside paint method");
        try {
            int i = 0;
            scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                g.drawString(scanner.nextLine(), 100, 100 + i);
                i += 30;
            }
        } catch (FileNotFoundException ex) {
            System.out.println("Exception " + ex);
        }

        System.out.println("Reading file and showing at applet");
    }
    public void stop() {
        System.out.println("Inside stop method");
    }

    public void destroy() {
        scanner.close();
        System.out.println("Inside destroy method: closed scanner object");
    }
}

import java.applet.Applet;

import java.awt.Graphics;

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;

</applet>

public class AppletLifeCycle extends Applet {

File file;

Scanner scanner;

public void init() {

sb = new StringBuffer();

file = new File("D:\\test.txt");

System.out.println("Inside init method: created StringBuffer and File Object");

}

public void start() {

System.out.println("Inside start method");

}

public void paint(Graphics g) {

System.out.println("Inside paint method");

try {

int i = 0;

scanner = new Scanner(file);

while (scanner.hasNextLine()) {

g.drawString(scanner.nextLine(), 100, 100 + i);

i += 30;

}

} catch (FileNotFoundException ex) {

System.out.println("Exception " + ex);

}

System.out.println("Reading file and showing at applet");

}

public void stop() {

System.out.println("Inside stop method");

}

public void destroy() {

scanner.close();

System.out.println("Inside destroy method: closed scanner object");

}

Output

Inside init method: created StringBuffer and File Object
Inside start method
Inside paint method
Reading file and showing at applet
Inside stop method
Inside destroy method: closed scanner object

Inside init method: created StringBuffer and File Object