抽象方法和抽象类（49）

abstract class Fig {
	protected int x, y;
	//定义抽象方法
	abstract double area();
	Fig(int a, int b) {
		x = a;
		y = b;
	}
}

class Rect extends Fig {
	//调用父类构造方法
	Rect(int a, int b) {
		super(a, b);
	}
	//计算矩形面积
	double area() {
		return x * y;
	}
}

class Tria extends Fig {
	//调用父类构造方法
	Tria(int a, int b) {
		super(a,b);
	}
	//计算三角形面积
	double area() {
		return 0.5 * x * y;
	}
}

public class ExtendsProject {
	//定义静态方法
	public static void useArea(Fig f) {
		System.out.println("f.area()=" + f.area());
	}
	
	public static void main(String argv[]) {
		Rect r = new Rect(8, 6);
		Tria t = new Tria(8, 6);
		Fig f;
		f = r;
		useArea(f);
		
		f = t;
		useArea(f);
	}
}