java例子5：平面圆，继承圆

[root@gdc1000 java]# cat PlaneCircle.java 
public class PlaneCircle extends Circle {
	public double cx, cy;
	public PlaneCircle ( double r, double x, double y) {
		super.r = r;
		this.cx = x;
		this.cy = y;
	}

	public boolean isInside(double x, double y) {
		double dx = x - cx, dy = y - cy;
		double distance = Math.sqrt(dx*dx + dy*dy);
		return (distance < r);
	}
} 
[root@gdc1000 java]# 

[root@gdc1000 java]# cat PlaneTest.java 
public class PlaneTest {
	public static void main(String[] args) {
		int input = 0;
		if(0 == args.length)
                {
			System.out.println("default input");
			input = 0;		
		}
		else
		{
			input = Integer.parseInt(args[0]);
		}	
		PlaneCircle c = new PlaneCircle(input, 0, 0);
		System.out.println(c.area());
		System.out.println(c.isInside(3,5));
	}
	
}

这里使用了super, this分别指代类中不同的关系，父亲，自己。

使用了extends关键词