Introduction

Content

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Examples of class methods

In the same way that a class can provide variables and constants, a class can also provide useful methods that do not require an object of the class.

An example of a class method used in previous units is:

nextGuess = Math.random();

This example is a method that returns a random value from 0.0 up to (but not including) 1.0. There is no need for an instance of the Math class for some other object to use this public static method.

We could define a class method addUp() for a class Counter, that when provided with an integer returns the total of numbers. For example, if provided with the number 3, would return (1 + 2 + 3) = 6. Such a class and its public static method would look as follows:

public class Counter

  {

  public static int addUp( int limit )

    {

    int total = 0;

    int i = 1;

    while( i <= limit)

      {

      total += i;

      i = i + 1;

      }

      return total;

    }

  }

An applet to make use of this class method, without creating an instance of the class, is as follows:

// <APPLET code="ClassMethodApplet.class" width=275 height=200></APPLET>

import java.applet.Applet;

import java.awt.*;

public class ClassMethodApplet extends Applet

  {

  public void paint (Graphics g)

    {

    int x = 20;

    int y = 20;

    // use Class method 'addUp()'

    int result = Counter.addUp( 4 );

    g.drawString("result = " + result, x, y);

    }

  }

Notice how there is never an instance of the class Counter created. The class method is invoked through the sending of a message to the Counter class itself:

Counter.addUp( 4 )

	Activity 1 ?Geometric class constants Activity 2 ?Factorial class Activity 3 ?SavingsAccount class
	Exercise 6 ?DiceThrower

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