因为第一期的代码和解释很清楚了，本次直接上代码

1. 建立一个抽象Shape类，有Circle（圆形）和Rect（矩形）子类。Shape类有zhouchang()和area()两种抽象方法。

Rect类有cha()方法用于比较长宽的差,若长大于宽输出“长比宽大”，否则输出“宽比长大”。（正方形）Squ为Rect子类，在Squ类中，重写cha（）方法，并输出“长等于宽”

要求：

要提供Circle和Rect类重写父类Shape的zhouchang()和area()方法。

Circle类要有静态常量PI。

为Circle类，Rect类，Squ类提供构造方法，为属性赋初值。

编写测试类，测试上述程序。

 1.创建Shape

public abstract class Shape {

	public abstract void zhouchang();
	public abstract void area();
	private double dLong = 0;
	private double width = 0;
	private double height = 0;
	
	public double getdLong() {
		return dLong;
	}
	public void setdLong(double dLong) {
		this.dLong = dLong;
	}
	public double getWidth() {
		return width;
	}
	public void setWidth(double width) {
		this.width = width;
	}
	public double getHeight() {
		return height;
	}
	public void setHeight(double height) {
		this.height = height;
	}
	
}

 2.创建Circle

public class Circle extends Shape{
	static double IP=3.14;
	@Override
	public void zhouchang() {
		System.out.println(2*IP*this.getHeight());
	}
	@Override
	public void area() {
		System.out.println(IP*IP*this.getHeight());
	}
	public void cha() {
		System.out.print("圆的周长：");
		zhouchang();
		System.out.print("圆的面积：");
		area();
	}
	public Circle(double height) {
		 System.out.print("自动赋值：");
		   this.setHeight(height);
	}
}

 3.创建Rect

public class Rect extends Shape{
	@Override
	public void zhouchang() {
		// TODO Auto-generated method stub
		System.out.println("周长为："+(double)2*this.getdLong()+(double)2*this.getWidth());
	}
	@Override
	public void area() {
		// TODO Auto-generated method stub
		System.out.println("面积为："+this.getdLong()*this.getWidth());
	}
	public void cha() {
		double result = this.getdLong()-this.getWidth();
		String shape="长为"+this.getdLong()+"宽为"+this.getWidth();
		String str="";
		if(result>0){
		  str=",此图形为长方形。";
		}
		else{
		   str=",长等于宽，此图形为正方形。";
		}
		System.out.println(shape+str);
	}
	 public Rect(double dlong,double width) {
		   System.out.print("自动赋值：");
		   this.setdLong(dlong);
		   this.setWidth(width);
		 }
}

 4.创建Squ

public class Squ extends Rect{
	public Squ(double dlong, double width) {
		super(dlong, width);
	}
	private void cah() {
		//如果需要重写
	}
}

5.RectTest测试类

package test4;

public class RectTest {
	 public static void main(String[] args) {
		  Rect rect = new Rect(25,20);
		  rect.cha();
		  
		  Circle circle=new Circle(10);
		  circle.cha();
		 }
}

 运行截图：