我的java学习-多态和继承

原创于 2018-10-16 22:19:09 发布 · 172 阅读

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本文通过实例演示了Java中多态的概念，展示了如何通过继承抽象类Shape并重写getArea方法来实现不同形状面积的计算。涉及Circle、Rectangle、Triangle和Ladder等类的定义及使用。

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一直以来，我都以为java的多态主要表现在由于方法所自带的参数，类型不同，数目多少不同而带来的同名称方法的重用。
原来还有对抽象类方法的继承和重写，也是多态的一种表现。
下面的代码里面，几个类class都是继承了Shape类，同时重写了里面的getArea方法，也是一种多态的表现。

abstract class Shape {
public abstract double getArea();
}

class Circle extends Shape{
    private double r;
    public Circle(double r){
        this.r = r;
    }
    public double getArea(){
        return 3.14 * r * r;
    }
}
class Rectangle extends Shape{
    private double a, b;
    public Rectangle(double a, double b){
        this.a = a;
        this.b = b;
    }
    public double getArea(){
        return a * b;
    }
}
class Triangle extends Shape{
    private double a, b, c;
    public Triangle(double a, double b, double c){
        this.a = a;
        this.b = b;
        this.c = c;
    }
    public double getArea(){
        double temp = 0.5 * (a + b + c);
        return Math.sqrt(temp * (temp -a) * (temp -b) *(temp -c));
    }
}
class Ladder extends Shape{
     private double a, b, h;
    public Ladder(double a, double b, double h){
        this.a = a;
        this.b = b;
        this.h = h;
    }
    public double getArea(){        
        return 0.5 * (a + b) * h;
    }
}

public class Test2{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        
        System.out.println("请输入圆的半径：");
        double r = sc.nextDouble();
        Shape area1 = new Circle(r);
        System.out.println("圆的面积是：" + area1.getArea());
        
        System.out.println("请输入矩形的两条边长，回车键分隔：");
        double a1 = sc.nextDouble();
        double a2 = sc.nextDouble();
        Shape area2 = new Rectangle(a1, a2);
        System.out.println("矩形的面积是" + area2.getArea());
        
        System.out.println("请输入梯形的上下边长和高，回车键分隔：");
        double b1 = sc.nextDouble();
        double b2 = sc.nextDouble();
        double b3 = sc.nextDouble();
        Shape area3 = new Ladder(b1, b2, b3);
        System.out.println("梯形的面积是：" + area3.getArea());
        
        System.out.println("请输入三角形的三条边，回车键分隔：");
        double c1 = sc.nextDouble();
        double c2 = sc.nextDouble();
        double c3 = sc.nextDouble();
        Shape area4 = new Triangle(c1, c2, c3);
        System.out.println("三角形的面积是：" + area4.getArea());
        
        double area = area1.getArea() + area2.getArea() +
                area3.getArea() + area4.getArea();
        System.out.println("几个图形面积的和是：" + area);
    }    
}