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     @Override38     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     @Override48     double area(){49         return 0.0796*a*a;50     }51 }