定义一个抽象类 Shape，其中包含求形状的面积和周长的抽象方法。定义三角形、矩形、圆形类，继承Shape。分别创建一个三角形、矩形、圆形对象，输出各类图形的面积和周长。三角形是常规三角形。JAVA

首先，在Java中，你可以通过定义一个抽象类`Shape`来实现多态和抽象方法的概念。抽象类不能实例化，它通常包含一些抽象方法，这些方法没有具体实现，需要在它的子类中提供。以下是代码的一个例子：

// 定义抽象类 Shape
abstract class Shape {
    abstract double getArea(); // 抽象方法，计算面积
    abstract double getPerimeter(); // 抽象方法，计算周长

    // 具体方法，打印信息
    void printDetails() {
        System.out.println("This is an abstract shape.");
    }
}

// 定义具体的三角形类，继承自 Shape
class Triangle extends Shape {
    private double base;
    private double height;

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

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

    @Override
    double getPerimeter() {
        // 仅举一例，实际取决于三角形的具体类型
        return base + Math.sqrt(Math.pow(height, 2) + Math.pow(base / 2, 2));
    }

    @Override
    void printDetails() {
        System.out.println("Triangle with base " + base + " and height " + height);
    }
}

// 矩形类，同样继承 Shape
class Rectangle extends Shape {
    private double width;
    private double length;

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

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

    @Override
    double getPerimeter() {
        return 2 * (width + length);
    }

    @Override
    void printDetails() {
        System.out.println("Rectangle with width " + width + " and length " + length);
    }
}

// 圆形类，继承 Shape
class Circle extends Shape {
    private double radius;

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

    @Override
    double getArea() {
        return Math.PI * Math.pow(radius, 2);
    }

    @Override
    double getPerimeter() {
        return 2 * Math.PI * radius;
    }

    @Override
    void printDetails() {
        System.out.println("Circle with radius " + radius);
    }
}

// 创建对象并输出信息
public static void main(String[] args) {
    Triangle triangle = new Triangle(3, 4);
    rectangle = new Rectangle(5, 6);
    circle = new Circle(2);

    triangle.printDetails();
    System.out.println("Triangle area: " + triangle.getArea());
    System.out.println("Triangle perimeter: " + triangle.getPerimeter());

    rectangle.printDetails();
    System.out.println("Rectangle area: " + rectangle.getArea());
    System.out.println("Rectangle perimeter: " + rectangle.getPerimeter());

    circle.printDetails();
    System.out.println("Circle area: " + circle.getArea());
    System.out.println("Circle perimeter: " + circle.getPerimeter());
}