JAVA的多态

多态

abstract class MyShape {
    public abstract void getArea();

    public abstract void getLength();
}

class Circle extends MyShape {

    public static final double PI = 3.14;
    double r;

    public Circle(double r) {
        this.r = r;
    }

    public void getArea() {
        System.out.println("圆形的面积：" + PI * r * r);
    }

    public void getLength() {
        System.out.println("圆形的周长：" + 2 * PI * r);
    }
}

class Rect extends MyShape {

    int width;
    int height;

    public Rect(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public void getArea() {
        System.out.println("矩形的面积：" + width * height);
    }

    public void getLength() {
        System.out.println("矩形的周长：" + 2 * (width + height));
    }
}

public class Demo {
    // 1、定义一个函数接收任意类型的图形对象
    public static void printThe(MyShape s) {
        s.getArea();
        s.getLength();
    }

    // 2、定义一个函数返回任意类型的图形对象
    public static MyShape getSharp(int i) {
        if (i == 0) {
            return new Circle(4.0);
        } else {
            return new Rect(3, 4);
        }
    }

    public static void main(String[] args) {
        Circle c = new Circle(4.0);
        printThe(c);
        Rect r = new Rect(3, 4);
        printThe(r);

        MyShape ms = getSharp(0);
        ms.getArea();
        ms.getLength();
    }
}