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.javapackage 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 */ public void move(int deltax, int deltay) { x1 += deltax; x2 += deltax; y1 += deltay; y2 += deltay; } /** Test whether the specified point is inside the rectangle */ public boolean isInside(int x, int y) { return ((x >= x1)&& (x <= x2)&& (y >= y1)&& (y <= y2)); } /** * Return the union of this rectangle with another. I.e. return the * smallest rectangle that includes them both. **/ public Rect union(Rect r) { return new Rect((this.x1 < r.x1) ? this.x1 : r.x1, (this.y1 < r.y1) ? this.y1 : r.y1, (this.x2 > r.x2) ? this.x2 : r.x2, (this.y2 > r.y2) ? this.y2 : r.y2); } /** * Return the intersection of this rectangle with another. * I.e. return their overlap. **/ public Rect intersection(Rect r) { Rect result = new Rect((this.x1 > r.x1) ? this.x1 : r.x1, (this.y1 > r.y1) ? this.y1 : r.y1, (this.x2 < r.x2) ? this.x2 : r.x2, (this.y2 < r.y2) ? this.y2 : r.y2); if (result.x1 > result.x2) { result.x1 = result.x2 = 0; } if (result.y1 > result.y2) { result.y1 = result.y2 = 0; } return result; } /** * This is a method of our superclass, Object. We override it so that * Rect objects can be meaningfully converted to strings, can be * concatenated to strings with the + operator, and can be passed to * methods like System.out.println( ) **/ public String toString( ) { return "[" + x1 + "," + y1 + "; " + x2 + "," + y2 + "]"; } } |