public class Test {

    public static void main(String[] args) {

    //创建类的实例，并分别对圆的半径和矩形的长宽进行赋值

    Rectangle rectangle=new Rectangle(5,6);

    Circle  circle=new  Circle(3.5);

//调用area（）方法，输出结果

    System.out.println("圆的面积为："+circle.area());

    System.out.println("矩形的面积为："+rectangle.area());

}

}

//抽象类Shape，里面含抽象方法area( )

public abstract class Shape {

public abstract double area();

}

public class Rectangle extends Shape {

    //属性：矩形的长lenghth、宽wide

private double lenghth;

private double wide;

//创建带参构造方法以及无参构造方法

  public  Rectangle() {

  }

public Rectangle(double lenghth, double wide) {

super();

this.lenghth = lenghth;

this.wide = wide;

}

    //创建针对长、宽的赋值和取值方法

public double getLenghth() {

return lenghth;

}

public void setLenghth(double lenghth) {

this.lenghth = lenghth;

}

public double getWide() {

return wide;

}

public void setWide(double wide) {

this.wide = wide;

}

//重写父类的area（）方法

public double area() {

return lenghth*wide;

}

}

public class Circle extends Shape {

    //属性：圆的半径r

private double r;

    //创建带参构造方法以及无参构造方法

public Circle(double r) {

super();

this.r = r;

}

public Circle() {

super();

}

    //创建针对半径的赋值和取值方法

public double getR() {

return r;

}

public void setR(double r) {

this.r = r;

}

//重写父类中area()方法

public double area() {

return Math.PI*r*r;

}

}