• AdditionApplet.java
    
    // Fig. 3.13: AdditionApplet.java
    // Adding two floating-point numbers.
    
    // Java packages
    import java.awt.Graphics;   // import class Graphics
    import javax.swing.*;       // import package javax.swing
    
    public class AdditionApplet extends JApplet {
       double sum;  // sum of values entered by user
    
       // initialize applet by obtaining values from user
       public void init()
       {
          String firstNumber;   // first string entered by user
          String secondNumber;  // second string entered by user
    
          double number1;       // first number to add
          double number2;       // second number to add
    
          // obtain first number from user
          firstNumber = JOptionPane.showInputDialog(
             "Enter first floating-point value" );
    
          // obtain second number from user
          secondNumber = JOptionPane.showInputDialog(
             "Enter second floating-point value" );
    
          // convert numbers from type String to type double
          number1 = Double.parseDouble( firstNumber ); 
          number2 = Double.parseDouble( secondNumber );
    
          // add numbers
          sum = number1 + number2;
    
       } // end method init
    
       // draw results in a rectangle on applet background
       public void paint( Graphics g )
       {
          // call superclass version of method paint
          super.paint( g );
    
          // draw rectangle starting from (15, 10) that is 270 
          // pixels wide and 20 pixels tall
          g.drawRect( 15, 10, 270, 20 );
    
          // draw results as a String at (25, 25)
          g.drawString( "The sum is " + sum, 25, 25 );
    
       } // end method paint
    
    } // end class AdditionApplet