用eclipse实现定义抽象类Shape及其子类矩形Rect类和圆形Ciecle类,在main()实现实例化子类,键盘输入半径的值,输出宽=4,高=4的矩形面积,键盘输入半径的值,输出圆的面积,小数位数默认,所有计算均通过调用类的

方法实现。

以下是示例代码：

// Shape.java
public abstract class Shape {
    public abstract double getArea();
}

// Rect.java
public class Rect extends Shape {
    private double width;
    private double height;
    
    public Rect(double width, double height) {
        this.width = width;
        this.height = height;
    }

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

// Circle.java
public class Circle extends Shape {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

// Main.java
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // 实例化矩形对象并计算面积
        Rect rect = new Rect(4, 4);
        System.out.println("矩形面积为：" + rect.getArea());
        
        // 实例化圆形对象并计算面积
        System.out.print("请输入圆的半径：");
        double radius = scanner.nextDouble();
        Circle circle = new Circle(radius);
        System.out.println("圆的面积为：" + circle.getArea());
        
        scanner.close();
    }
}

运行结果：

矩形面积为：16.0
请输入圆的半径：5
圆的面积为：78.53981633974483