java的抽象类的三角形周长_怎么使用Java把抽象类改为接口计算三角形，长方形，圆形的面积？...

抽象类的三角形周长计算代码示例：

abstract class Triangle {
    protected double a, b, c;

    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    public abstract double getPerimeter();
}

class ConcreteTriangle extends Triangle {
    public ConcreteTriangle(double a, double b, double c) {
        super(a, b, c);
    }

    public double getPerimeter() {
        return a + b + c;
    }
}

public class Main {
    public static void main(String[] args) {
        Triangle t = new ConcreteTriangle(3, 4, 5);
        System.out.println("Triangle perimeter: " + t.getPerimeter());
    }
}

将抽象类改为接口，代码示例：

interface Shape {
    double getArea();
}

class Triangle implements Shape {
    private double a, b, c;

    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    public double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }
}

class Rectangle implements Shape {
    private double length, width;

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

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

class Circle implements Shape {
    private double radius;

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

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

public class Main {
    public static void main(String[] args) {
        Shape[] shapes = {new Triangle(3, 4, 5), new Rectangle(2, 3), new Circle(1)};
        for (Shape s : shapes) {
            System.out.println("Area: " + s.getArea());
        }
    }
}

在这个示例中，我们创建了一个 `Shape` 接口，它有一个 `getArea()` 方法。我们创建了三个具体的形状类 `Triangle`、`Rectangle` 和 `Circle`，它们都实现了 `Shape` 接口，并实现了 `getArea()` 方法。在 `Main` 类中，我们创建了一个 `Shape` 数组，并用具体的形状类的实例填充它。然后，我们循环遍历这个数组，调用每个形状的 `getArea()` 方法并打印结果。