Java Examples in a Nutshell, 3rd Edition

A Rectangle Class

Example 2-1 shows a class that represents a rectangle. Each instance of this Rect class has four fields, x1, y1, x2, and y2, that define the coordinates of the corners of the rectangle. The Rect class also defines a number of methods that operate on those coordinates.

Note the toString( ) method. This method overrides the toString( ) method of java.lang.Object, which is the implicit superclass of the Rect class. toString( ) produces a String that represents a Rect object. As you’ll see, this method is quite useful for printing out Rect values.

Example 2-1. Rect.java

package je3.classes; /** * This class represents a rectangle. Its fields represent the coordinates * of the corners of the rectangle. Its methods define operations that can * be performed on Rect objects. **/ public class Rect { // These are the data fields of the class public int x1, y1, x2, y2; /** * The is the main constructor for the class. It simply uses its arguments * to initialize each of the fields of the new object. Note that it has * the same name as the class, and that it has no return value declared in * its signature. **/ public Rect(int x1, int y1, int x2, int y2) { this.x1 = x1; this.y1 = y1; this.x2 = x2; this.y2 = y2; } /** * This is another constructor. It defines itself in terms of the above **/ public Rect(int width, int height) { this(0, 0, width, height); } /** This is yet another constructor. */ public Rect( ) { this(0, 0, 0, 0); } /** Move the rectangle by the specified amounts ...