试对平面直角坐标上的点，线段，三角形等图形编写一个程序，并在程序中求出对应图形的面积和周长

对于平面直角坐标系上的简单图形，如点、线段和三角形，我们可以先创建对应的类来存储它们的信息。以下是简化版的示例代码，用于计算点、线段和基础类型的三角形（非共线三点构成）的面积和周长：

import java.awt.geom.Point2D;

// 点类
class Point {
    double x, y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "(" + x + ", " + y + ")";
    }
}

// 线段类
class LineSegment {
    Point start, end;

    public LineSegment(Point start, Point end) {
        this.start = start;
        this.end = end;
    }

    public double length() {
        return Math.sqrt(Math.pow(end.x - start.x, 2) + Math.pow(end.y - start.y, 2));
    }

    @Override
    public String toString() {
        return "Line from " + start + " to " + end;
    }
}

// 三角形类，基于三点
class Triangle {
    Point a, b, c;

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

    public double area() {
        double sideA = lineLength(a, b);
        double sideB = lineLength(b, c);
        double sideC = lineLength(c, a);
        double s = (sideA + sideB + sideC) / 2; // 半周长
        return Math.sqrt(s * (s - sideA) * (s - sideB) * (s - sideC));
    }

    public double perimeter() {
        return lineLength(a, b) + lineLength(b, c) + lineLength(c, a);
    }

    private double lineLength(Point p1, Point p2) {
        return Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
    }

    @Override
    public String toString() {
        return "Triangle with vertices at " + a + ", " + b + ", and " + c;
    }
}

public class Main {
    public static void main(String[] args) {
        Point point = new Point(0, 0);
        LineSegment segment = new LineSegment(new Point(0, 0), new Point(1, 1));
        Triangle triangle = new Triangle(new Point(0, 0), new Point(1, 0), new Point(0, 1));

        System.out.println("Point area: " + point.getArea()); // 点没有面积，此处假设为0
        System.out.println("Segment length: " + segment.length());
        System.out.println("Triangle area: " + triangle.area());
        System.out.println("Triangle perimeter: " + triangle.perimeter());
    }
}

请注意，这里的点类没有面积属性，因为点没有面积。实际上，我们在这里计算的是线段长度和三角形面积。在实际应用中，可能会需要更复杂的几何库来精确处理各种形状。