1.图形类

package com.yfs.javase;public class Shape {	//计算面积方法	public double getArea() {		System.out.println("计算面积");		return 0;	}}

 2.圆

package com.yfs.javase;public class Circle extends Shape {		private double r;		public Circle(double r) {		this.r = r;		System.out.println("创建圆形面积");	}		public double getArea() {//覆盖父类的方法		System.out.println("计算圆形面积...");		return 3.14 * r * r;	}}

 3.矩形

package com.yfs.javase;public class Rangton  extends Shape {		private double width;	private double length;		public Rangton(double width, double length) {		this.width = width;		this.length = length;		System.out.println("创建矩形面积");	}		public double getArea() {		System.out.println("计算矩形面积...");		return width * length;	}}

 4.三角形

package com.yfs.javase;public class Trantangle  extends Shape {		private double height;	private double width;		public Trantangle(double height, double width) {		this.height = height;		this.width = width;		System.out.println("创建三角形面积");	}		public double getArea() {		System.out.println("计算三角形面积...");		return 1.0 / 2 * width * height;	}}

 5.测试

package com.yfs.javase;import java.util.Random;public class Test1 {	/**	 * 编写一个图形类，提供计算面积的方法。	 * 通过继承图形类，封装三角形，圆形，正方形类，	 * 覆盖父类的方法。在测试类里随机产生10个图形，	 * 面积求和。	 */	public static void main(String[] args) {		Shape[]  shapes = new Shape[10];//存放子类对象		Random ran = new Random();		double sum = 0;		//创建随即图形		for (int i = 0; i < shapes.length; i++) {			int r = ran.nextInt(101);			if(r > 65) {				shapes[i] = new Circle(ran.nextInt(10));			} else if( r > 35 ){				shapes[i] = new Rangton(ran.nextInt(10),ran.nextInt(10));				//shapes[i].setWidth();			} else {				shapes[i] = new Trantangle(ran.nextInt(10), ran.nextInt(10));			}		}		System.out.println("================");		//计算随机图形面积		for (int i = 0; i < shapes.length; i++) {//			Circle c = (Circle)shapes[i];//			sum += c.getArea();			sum += shapes[i].getArea();//子类对象计算面积		}		System.out.println("sum = " + sum);	}}