Triangle2D类（Java）

Triangle2D类是一个表示二维平面上三角形的类，具体实现如下：

public class Triangle2D {
    private MyPoint p1, p2, p3; // 三个顶点

    // 构造函数
    public Triangle2D(double x1, double y1, double x2, double y2, double x3, double y3) {
        p1 = new MyPoint(x1, y1);
        p2 = new MyPoint(x2, y2);
        p3 = new MyPoint(x3, y3);
    }

    // 计算周长
    public double getPerimeter() {
        double side1 = p1.distance(p2);
        double side2 = p2.distance(p3);
        double side3 = p3.distance(p1);
        return side1 + side2 + side3;
    }

    // 计算面积
    public double getArea() {
        double s = getPerimeter() / 2;
        double side1 = p1.distance(p2);
        double side2 = p2.distance(p3);
        double side3 = p3.distance(p1);
        return Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
    }

    // 判断点是否在三角形内部
    public boolean contains(MyPoint point) {
        double x = point.getX();
        double y = point.getY();

        double x1 = p1.getX();
        double y1 = p1.getY();
        double x2 = p2.getX();
        double y2 = p2.getY();
        double x3 = p3.getX();
        double y3 = p3.getY();

        double alpha = ((y2 - y3)*(x - x3) + (x3 - x2)*(y - y3)) /
                       ((y2 - y3)*(x1 - x3) + (x3 - x2)*(y1 - y3));
        double beta = ((y3 - y1)*(x - x3) + (x1 - x3)*(y - y3)) /
                      ((y2 - y3)*(x1 - x3) + (x3 - x2)*(y1 - y3));
        double gamma = 1.0 - alpha - beta;

        return alpha > 0 && beta > 0 && gamma > 0;
    }

    // 判断两个三角形是否相等
    public boolean equals(Triangle2D t) {
        double x1 = p1.getX();
        double y1 = p1.getY();
        double x2 = p2.getX();
        double y2 = p2.getY();
        double x3 = p3.getX();
        double y3 = p3.getY();

        double tx1 = t.getP1().getX();
        double ty1 = t.getP1().getY();
        double tx2 = t.getP2().getX();
        double ty2 = t.getP2().getY();
        double tx3 = t.getP3().getX();
        double ty3 = t.getP3().getY();

        return x1 == tx1 && y1 == ty1 && x2 == tx2 && y2 == ty2 && x3 == tx3 && y3 == ty3;
    }

    // 获取三个顶点
    public MyPoint getP1() {
        return p1;
    }

    public MyPoint getP2() {
        return p2;
    }

    public MyPoint getP3() {
        return p3;
    }
}

在这个类中，我们实现了计算三角形周长和面积的方法，并且实现了判断一个点是否在三角形内部的方法。我们还实现了判断两个三角形是否相等的方法，以及获取三个顶点的方法。