java - day12 - ShapeTest

　　抽象类的定义及使用

抽象类不能实例化，但抽象类名的数组类型可以，见案例

 package com.example;

 public class ShapeTest {
     public static void main(String[] args){
         Shape[] shapes = new Shape[3];  //shape为抽象类，不可以实例化；shape[]为数组类，可以实例化
         shapes[0] = new Square(3.1);
         shapes[1] = new Circle(1.5);
         shapes[2] = new Circle(2.4);
         ShapeTest x = new ShapeTest();
         System.out.println(x.areaMax(shapes));
     }

     double areaMax(Shape[] shapes){
         double areamax = shapes[0].area();
         for(int i=0;i<shapes.length;i++){
             double max = shapes[i].area();
             if(max>areamax){
                  areamax = max;
             }
         }
         return areamax;
     }
 }

 abstract class Shape{
     double a;
     abstract double area();
 }

 //子类继承父类抽象方法--重写
 class Square extends Shape{
     Square(double a){
             this.a = a;
         }
     }
     @Override
     double area(){
         return 0.0625*a*a;
     }
 }

 class Circle extends Shape{
     Circle(double a){
         this.a = a;
     }
     @Override
     double area(){
         return 0.0796*a*a;
     }
 }