java

　　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
 1 package com.example;
 2 
 3 
 4 public class ShapeTest {
 5     public static void main(String[] args){
 6         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
 7         shapes[0] = new Square(3.1);
 8         shapes[1] = new Circle(1.5);
 9         shapes[2] = new Circle(2.4);
10         ShapeTest x = new ShapeTest();
11         System.out.println(x.areaMax(shapes));
12     }
13 
14     double areaMax(Shape[] shapes){
15         double areamax = shapes[0].area();
16         for(int i=0;i<shapes.length;i++){
17             double max = shapes[i].area();
18             if(max>areamax){
19                  areamax = max;
20             }
21         }
22         return areamax;
23     }
24 }
25 
26 abstract class Shape{
27     double a;
28     abstract double area();
29 }
30 
31 //子类继承父类抽象方法--重写
32 class Square extends Shape{
33     Square(double a){
34             this.a = a;
35         }
36     }
37     @Override
38     double area(){
39         return 0.0625*a*a;
40     }
41 }
42 
43 class Circle extends Shape{
44     Circle(double a){
45         this.a = a;
46     }
47     @Override
48     double area(){
49         return 0.0796*a*a;
50     }
51 }