问题：
编写一个抽象类Shape,声明计算图形面积的抽象方法。再分别定义Shape的子类Circle(圆)和
答案：
public abstract class AShape { public abstract double getArea(); } public class Cycle extends AShape { public double radius=3.0; public double getArea() { System.out.println("compute a cycle's area:"+3.14*radius*radius); return 3.14*radius*radius; } } public class Square extends AShape { public double length=2.0; @Override public double getArea() { // TODO Auto-generated method stub System.out.println("compute a square's area:"+length* length); return length* length; } }