The Applet will give the result of adding two fractions together - but still lacks a great deal of meaningful functionality.

Nothing different here, except there are a lot more objects on the screen.

Set up a panel with GridLayout to hold the labels and boxes in two rows and three columns.

Call the Fraction constructor with two ints to create new Fraction objects a and b.

Add them together.

An Applet to demonstrate the working of the Fraction Class:

Source code: TestFraction.java

import java.applet.Applet;
 import java.awt.*;
 import java.awt.event.*;
 /**
 * Tests the operation of the Fraction Class
 *
 * @author Mr J
 * @version 20040212
 */
 public class TestFraction extends Applet implements ActionListener
 {
   // input boxes
   Label topLabel = new Label("Numerators:");
   Label botLabel = new Label("Demoninators:");
   TextField n1 = new TextField("n1");
   TextField n2 = new TextField("n2");
   TextField d1 = new TextField("d1");
   TextField d2 = new TextField("d2");

   private Button addButton = new Button("Add");
   private Label greeting = new Label("Applet that adds two fractions");

  /**
   * Add objects to the Applet
   */
   public void init()
   {
     Panel inputPanel = new Panel();
     inputPanel.setLayout(new GridLayout(2, 3));
     inputPanel.add(topLabel);
     inputPanel.add(n1);
     inputPanel.add(n2);
     inputPanel.add(botLabel);
     inputPanel.add(d1);
     inputPanel.add(d2);
     add(inputPanel);
     add(addButton);
     add(greeting);
     // Causes button presses to be detected
     addButton.addActionListener(this);
   }
   /**
   * When an event occurs on an object with an ActionListener attached,   * this method is carried out.
   *
   * @param e carries details about the event that occurred
   */
   public void actionPerformed(ActionEvent e)
   {
     // Get the data from the boxes and make the fraction objects
     Fraction a = new Fraction( Integer.parseInt(n1.getText()),
                                Integer.parseInt(d1.getText()) );
     Fraction b = new Fraction( Integer.parseInt(n2.getText()),
                                Integer.parseInt(d2.getText()) );
     // add them together
     Fraction c = Fraction.add( a, b );
     greeting.setText("" + c.toString());
   }
}

Of course, our Fraction Class doesn't work too well, it doesn't have a lot of functionality and it doesn't reduce fractions (eg 10/25 is not reduced to 2/5 but we can always fix that later). However, hopefully it illustrates a few useful points about Classes and methods.

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On to selection - how to make choices in your code.

Related: [ Java Home | previous methods & classes | next:selection ]

To use, put the fractions in the box, the result of adding them appears in the label.

Students who complete this activity quickly might like to try to write a method that reduces a fraction to its lowest common denominator.

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