java新手笔记16 面积

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);

	}

}