additionapplet.java

经典的<<C how to program>一书第三版的例程。非常适合于C的初学者。

// Fig. 24.19: AdditionApplet.java
// Adding two floating-point numbers
import java.awt.Graphics;   // import class Graphics
import javax.swing.*;       // import package javax.swing

public class AdditionApplet extends JApplet {
   double sum;  // sum of the values entered by the user

   public void init()
   {
      String firstNumber,   // first string entered by user
             secondNumber;  // second string entered by user
      double number1,       // first number to add
             number2;       // second number to add

      // read in first number from user
      firstNumber =
         JOptionPane.showInputDialog(
            "Enter first floating-point value" );

      // read in 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 the numbers
      sum = number1 + number2;
   }

   public void paint( Graphics g )
   {
      // draw the results with g.drawString
      g.drawRect( 15, 10, 270, 20 );
      g.drawString( "The sum is " + sum, 25, 25 );
   }
}

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