5.22 JAVA 多态

几个点：

重载方法：要求子类中的方法 参数要和Super不同

覆盖方法：返回值类型 方法名 参数 都要和Super相同

/*
Online Java - IDE, Code Editor, Compiler

Online Java is a quick and easy tool that helps you to build, compile, test your programs online.
*/
abstract class Shape{
    String name;
    public Shape(){}
    public Shape(String name){
        this.name = name;
    }
    public abstract double getS();
    public abstract double getC();
}
class Circle extends Shape{
    private double radius;
    public Circle(){
        this(0.0);
    }
    public Circle(double radius){
        this.radius = radius;
    }
    public double getRadius(){
        return radius;
    }
    @Override
    public double getC(){
        return 2.0*Math.PI * radius;
    }
    @Override
    public double getS(){
        return Math.PI * radius * radius;
    }
    @Override
    public String toString(){
        return "[园] radius = "+ radius;
    }
}
class Rectangle extends Shape{
    private double radius;
    public Rectangle(){
        this(0.0);
    }
    public Rectangle(double radius){
        this.radius = radius;
    }
    public double getRadius(){
        return radius;
    }
    @Override
    public double getC(){
        return 4.0 * radius;
    }
    @Override
    public double getS(){
        return radius * radius;
    }
    @Override
    public String toString(){
        return "[正方形] radius = "+ radius;
    }
}
public class Main
{
    public static double Cal(Shape[] shapes){
        double s = 0;
        for(var shape : shapes){
            System.out.println(shape.getS());
            s = s + shape.getS();
        }
        return s;
    }
    public static void main(String[] args) {
        var shapes = new Shape[5];
        for(var i = 0; i < shapes.length; i++){
            var d = Math.random();
            if(d > 0.5)shapes[i] = new Circle(1);
            else shapes[i] = new Rectangle(2);
        }
        var s_s = Cal(shapes);
        System.out.printf("形状的总面积 = %.2f",s_s);
    }
}