ellipse1.java

《Java2程序设计实用教程(第2版)》课件

//【例3.8】  抽象类与抽象方法。

public class Ellipse1 extends PlaneGraphics1   //椭圆类 
{
    protected double radius_a;         //a轴半径
    protected double radius_b;         //b轴半径

    public Ellipse1(double radius_a, double radius_b)
    {                                  //构造方法
        super("椭圆");
        this.radius_a = radius_a;
        this.radius_b = radius_b;
    }

    public Ellipse1(double radius_a)   //圆是椭圆的特例
    {
        super("圆");
        this.radius_a = radius_a;
        this.radius_b = radius_a;
    }

    public Ellipse1()
    {
        this(0,0);
    }

    public double area()               //计算椭圆面积，实现父类的抽象方法
    {
        return Math.PI * this.radius_a * this.radius_b;
    }
}