Java Tech - Chapter 4

In this demo we begin with StartApplet4.java, which includes the classes Test1 and Test2, each of which implements an interface called Testable.

The classes implement aMethod() from Testable. We created a Testable array that references instances of Test1 and Test2. We loop through this array and invoke aMethod()to illustrate the power of an interface to add a common method to different classes.

InterfaceApplet.java
(Output goes to browser's Java console.)

public class InterfaceApplet extends java.applet.Applet
{
  public void init () {
    Testable [] array = new Testable[2];
    array[0] = new Test1 ();
    array[1] = new Test2 ();

    for (int i=0; i < 2; i++) {
        System.out.println ("Call aMethod() in Test" + array[i].aMethod ());
    }
  }

  // Paint message in Applet window.
  public void paint (java.awt.Graphics g) {
     g.drawString ("InterfaceApplet", 20, 20);
  }
}

/** Test1 implements Testable. **/
class Test1 implements Testable
{
  public int aMethod () {
    return 1;
  }
}

/** Test2 also implements Testable. **/
class Test2 implements Testable
{
  public int aMethod () {
    return 2;
  }
}

/** Testable interface holds one method. **/
interface Testable
{
  public int aMethod ();
}

InterfaceApp.java