/* * To change this template, choose Tools | Templates * and open the template in the editor. */package chenchao3;/** * * @author williechen */public class Ex4 {}interface Centered {    void setCenter(double x, double y);    double getCenterX();    double getCenterY();}class CenteredRectangle extends Rectangle implements Centered {    // New instance fields    private double cx,  cy;    // A constructor    public CenteredRectangle(double cx, double cy, double w, double h) {        super(w, h);        this.cx = cx;        this.cy = cy;    }    // We inherit all the methods of Rectangle but must    // provide implementations of all the Centered methods.     public void setCenter(double x, double y) {        cx = x;        cy = y;    }    public double getCenterX() {        return cx;    }    public double getCenterY() {        return cy;    }}class CenteredCircle extends Circle implements Centered {    // New instance fields    private double cx,  cy;    // A constructor    public CenteredCircle(double cx, double cy, double r) {        super(r);        this.cx = cx;        this.cy = cy;    }    // We inherit all the methods of Rectangle but must    // provide implementations of all the Centered methods.     public void setCenter(double x, double y) {        cx = x;        cy = y;    }    public double getCenterX() {        return cx;    }    public double getCenterY() {        return cy;    }}