利用接口多态和抽象类求圆 三角形 矩形 面积

可以定义一个抽象类 `Shape`，其中包含一个抽象方法 `getArea()`，用于计算形状的面积。然后分别创建三个子类 `Circle`、`Triangle` 和 `Rectangle` 并实现 `getArea()` 方法，以具体计算各自形状的面积。

以下是示例代码：

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

class Circle extends Shape {
    private double radius;

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

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

class Triangle extends Shape {
    private double base;
    private double height;

    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }

    @Override
    public double getArea() {
        return 0.5 * base * height;
    }
}

class Rectangle extends Shape {
    private double width;
    private double height;

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

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

然后在主函数中，我们可以通过多态的方式调用各个形状的 `getArea()` 方法，例如：

public static void main(String[] args) {
    Shape[] shapes = new Shape[] {
        new Circle(5),
        new Triangle(10, 3),
        new Rectangle(4, 6)
    };

    for (Shape shape : shapes) {
        System.out.println("Area of " + shape.getClass().getSimpleName() + " = " + shape.getArea());
    }
}

输出：

Area of Circle = 78.53981633974483
Area of Triangle = 15.0
Area of Rectangle = 24.0