9. 创建一个名为“shape”的抽象类，该类内部含有两个抽象方法getGirth(int i)和getArea(int i)，分别用来计算周长和面积；“shape”类派生出子类“triangle”，“triangle”类中按照三角形的周长和面积的计算方式对“shape”类中两个抽象方法进行覆盖，triangle构造方法具有六个参数，分别为三个顶点的横坐标和纵坐标，并在main方法中进行验证。请写出Shape、triangle类的源代码并设置用例计算输出三角形的周长和面积（注：可使用Math类）。Java程序

Shape.java文件：

public abstract class Shape {
    public abstract double getGirth(int i);
    public abstract double getArea(int i);
}

Triangle.java文件：

public class Triangle extends Shape {
    private double x1, y1, x2, y2, x3, y3;

    public Triangle(double x1, double y1, double x2, double y2, double x3, double y3) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
        this.x3 = x3;
        this.y3 = y3;
    }

    @Override
    public double getGirth(int i) {
        double a = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
        double b = Math.sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2));
        double c = Math.sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));
        return a + b + c;
    }

    @Override
    public double getArea(int i) {
        double a = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
        double b = Math.sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2));
        double c = Math.sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }
}

Main.java文件：

public class Main {
    public static void main(String[] args) {
        Triangle triangle = new Triangle(0, 0, 3, 0, 0, 4);
        System.out.println("三角形的周长为：" + triangle.getGirth(0));
        System.out.println("三角形的面积为：" + triangle.getArea(0));
    }
}

输出结果为：

三角形的周长为：12.0
三角形的面积为：6.0