What is Applet in Java? How to Create & Run?

Java applets are short programs created in Java or another programming language that combines Java bytecode and is provided to users as Java bytecode. Java applet was launched by the user from a web page, and it was then processed within a Java virtual machine (JVM) in a procedure distinct from the web browser. A Java applet might appear in a web page frame, a new application window, Sun’s AppletViewer, or a standalone applet testing tool.

Applets give interactive capabilities to web applications that HTML cannot deliver. They can record mouse input and feature controls such as buttons or checkboxes. In addition, an applet can modify the offered graphic information in response to user activities. As a result, applets are ideal for presentation, visualisation, and education.

An applet is a web application embedded in an HTML page with the APPLET or OBJECT tag and hosted on a web server. Applets are utilised to enhance the website’s dynamic and engaging nature.

 Example of an Applet

 import java.applet.*;

import java.awt.*;

public class MyApplet extends Applet

{

 int height, width;

 public void init()

 {

  height = getSize().height;

  width = getSize().width;

  setName(“MyApplet”);

 }

 public void paint(Graphics g)

 {

  g.drawRoundRect(10, 30, 120, 120, 2, 3);

 }

}

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 Here’s an example of a Java source code for making a simple calculator using an Applet. The result of the application is also presented below:

/*Java Program to Demonstrate a Basic Calculator using Applet*/

import java.awt.*;

import java.applet.*;

import java.awt.event.*;

public class Calculator extends Applet implements ActionListener

{

TextField inp;

//Function to add features to the frame

public void init()

{

         setBackground(Color.white);

         setLayout(null);

         int i;

         inp = new TextField();

         inp.setBounds(150,100,270,50);

         this.add(inp);

         Button button[] = new Button[10];

         for(i=0;i<10;i++)

         {

         button[i] = new Button(String.valueOf(9-i));

         button[i].setBounds(150+((i%3)*50),150+((i/3)*50),50,50);

         this.add(button[i]);

         button[i].addActionListener(this);

         }

         Button dec=new Button(“.”);

         dec.setBounds(200,300,50,50);

         this.add(dec);

         dec.addActionListener(this);

     Button clr=new Button(“C”);

         clr.setBounds(250,300,50,50);

         this.add(clr);

         clr.addActionListener(this)

         Button operator[] = new Button[5];

         operator[0]=new Button(“/”);

         operator[1]=new Button(“*”);

         operator[2]=new Button(“-“);

         operator[3]=new Button(“+”);

         operator[4]=new Button(“=”);

         for(i=0;i<4;i++)

         {

         operator[i].setBounds(300,150+(i*50),50,50);

         this.add(operator[i]);

         operator[i].addActionListener(this);

         }

         operator[4].setBounds(350,300,70,50);

         this.add(operator[4]);

         operator[4].addActionListener(this);

}

String num1=””;

String op=””;

String num2=””;

//Function to calculate the expression

public void actionPerformed(ActionEvent e)

{

         String button = e.getActionCommand();

     char ch = button.charAt(0);

         if(ch>=’0′ && ch<=’9’|| ch==’.’)

         {

         if (!op.equals(“”))

                     num2 = num2 + button;

         else

                     num1 = num1 + button;  

         inp.setText(num1+op+num2);

         }

         else if(ch==’C’)

         {

         num1 = op = num2 = “”;

         inp.setText(“”);

         }

         else if (ch ==’=’)

         {

         if(!num1.equals(“”) && !num2.equals(“”))

         {

                     double temp;

                 double n1=Double.parseDouble(num1);

                     double n2=Double.parseDouble(num2);

                     if(n2==0 && op.equals(“/”))

                     {

                     inp.setText(num1+op+num2+” = Zero Division Error”);

                     num1 = op = num2 = “”;

                     }

                     else

                     {

                     if (op.equals(“+”))

                         temp = n1 + n2;

                     else if (op.equals(“-“))

                         temp = n1 – n2;

                     else if (op.equals(“/”))

                         temp = n1/n2;

                     else

                         temp = n1*n2;

                     inp.setText(num1+op+num2+” = “+temp);

                     num1 = Double.toString(temp);

                     op = num2 = “”;

             }

         }

         else

         {

                     num1 = op = num2 = “”;

                     inp.setText(“”);

         }

     }

         else

         {

         if (op.equals(“”) || num2.equals(“”))

                     op = button;

         else

         {

                     double temp;

                     double n1=Double.parseDouble(num1);

                     double n2=Double.parseDouble(num2);

                     if(n2==0 && op.equals(“/”))

                     {

                     inp.setText(num1+op+num2+” = Zero Division Error”);

                     num1 = op = num2 = “”;

                     }

                     else

                     {

                     if (op.equals(“+”))

                         temp = n1 + n2;

                     else if (op.equals(“-“))

                         temp = n1 – n2;

                     else if (op.equals(“/”))

                         temp = n1/n2;

                     else

                         temp = n1*n2;

                     num1 = Double.toString(temp);

                     op = button;

                     num2 = “”;

             }

         }

         inp.setText(num1+op+num2);

     }

}

}

/*

<applet code = Calculator.class width=600 height=600>

</applet>

*/

</> Copy Code

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 Advantages of an Applet:

1. Since an applet is a short Java application, it is a platform-neutral code that can run on any browser.
2. On client-side computers, applets may execute various minor activities. They can play music, display images, receive user inputs, mouse clicks, and even keystrokes, among other things.
3. Applets are client-side visuals that are distinct and independent of the client-side platform.
4. Although applets are less in size than stand-alone applications, their ability to be shared across a network makes them more usable.
5. Since applets run on client browsers, they may import graphics and audio snippets depending on URLs.
6. Due to their access to resources, applets are highly secure.
7. Applets are safe and protected to use since they cannot modify the local system.
8. Applets operating via Intranets may perform multiple tiny activities such as login, inventory checking, and task scheduling.

 Limitations of an Applet:

 Since applets are received from distant workstations and might affect client-side machines, they are subject to several security constraints. Here are a few examples:

1. If someone is running an applet from an unreliable supplier, security is critical.
2. Any programme on the local system cannot be started or modified by the applet.
3. Applets do not have access to client-side resources such as files, operating systems, and so on.
4. Applets may be granted specific rights. They must be labelled as trustworthy applets and registered with APS (Applet Security Manager).
5. When it comes to interacting, Applet has few constraints. It can only communicate with the machine that loaded it.
6. Applets are unable to interact with native methods.
7. The only information an applet may collect about a client machine is its name, java edition, operating system, version, and so on.
8. Applets are notoriously sluggish to execute because all of the classes and resources they require must be sent across the network.