Question

用JAVA编写 声明一个基类Shape,在此基础上派生出Rectangle和Circle,二者都有GetArea()函数计算对象的面积.

Answer 1

public class Test{
public static void main(String args[]){

Shape rectangle = new Rectangle(3, 5);//长3宽5长方形
double rectangleArea = rectangle.getArea();
System.out.println("长3宽5的长方形面积是:" + rectangleArea);

Circle c = new Circle(3);//半径为3的圆
double circleArea = c.getArea();
System.out.println("半径为3的圆的面积为：" + circleArea);
}
}

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

class Rectangle extends Shape{
private double height; //长
private double width; //宽

public Rectangle(double h, double w){
this.height = h;
this.width = w;
}

public double getArea() {
return height * width;
}

}

class Circle extends Shape{
private static final double PI = Math.PI;//圆周率，可以替换为3.14的按照需求啦
private double r ;//半径

public Circle(double r){
this.r = r;
}

public double getArea() {
return PI * r *r;
}

}

-----------------测试结果
长3宽5的长方形面积是:15.0
半径为3的圆的面积为：28.274333882308138

Answer 2

abstract class Shape{
abstract double GetArea();
}
public class Rectangle extends Shape{
private double len,wid;
public double GetArea(){return len*wid;}
}
public class Circle extends Shape{
private double r;
public double GetArea(){ return r*r*3.14;}
}

Answer 3

abstract public class Shape
{
public Shape()
{
}

abstract public double GetArea();

}
public classCircle extends Shape
{
public double GetArea()
{
double are = 计算面积;
return are;
}
}

public class Rectangle extends Shape
{
public double GetArea()
{
double are = 计算面积;
return are;
}
}