以点类 Point 及平面图形类 Plane 为基础设计三角形类 Triangle

学习内容：以点类 Point 及平面图形类 Plane 为基础设计三角形类 Triangle

代码示例：

import java.util.Scanner;
class Point{
  private double x;
  private double y;
  public Point(double x,double y) {
    this.x=x;
    this.y=y;
    System.out.println("Point Constructor run");
  }
  public void setX(double x) {//设置x坐标
    this.x=x;
  }
  public final double getX(){//返回x坐标
    return x;
  }
  public void setY(double y) {//设置y坐标
    this.y=y;
  }
  public final double getY(){//返回y坐标
    return y;
  }
  public void show() {//显示点的坐标
    System.out.print("Point(X="+x+",Y="+y+")");
  }
  public double dis(Point p)
  {
    double _x = Math.abs(this.x - p.x);
    double _y = Math.abs(this.y - p.y);
    return Math.sqrt(_x*_x+_y*_y);
  }
}
abstract class Plane{//抽象类Plane
  double length() {
    return 0;
  }
  double area() {
    return 0;
  }
}
public class Triangle extends Plane { private Point a;
  private Point b;
  private Point c;
  public Triangle(final Point a, final Point b, final Point c) {
    this.a=a;
    this.b=b;
    this.c=c;
    System.out.println("Triangle Constructorrun");
  }
  public void setA(final Point a) {
    this.a=a;
  }
  public Point getA() {
    return a;
  }
  public void setB(final Point b) {
    this.b=b;
  }
  public Point getB() {
    return b;
  }
  public void setC(final Point c) {
    this.c=c;
  }
  public Point getC() {
    return c;
  }
  public final void show() {
    System.out.print("Triangle(A=");
    a.show();
    System.out.print(",B=");
    b.show();
    System.out.print(",C=");
    c.show();
  }
  final double area() {
    double l1, l2, l3,s;
    l1 = a.dis(b);
      l2 = a.dis(c);
      l3 = b.dis(c);
      s = (l1 + l2 + l3) / 2;
      double area=Math.sqrt(s * (s - l1) * (s - l2) * (s - l3));
      System.out.println("Area="+area);
      return 0;
  }
  final double length() {
    double l1=a.dis(b);
    double l2=a.dis(c);
    double l3=b.dis(c);
    double length=l1+l2+l3;
    System.out.println("length="+length);
        return 0;
  }
  public static void main(String[] args) {
    double x,y; 
    Point p1=new Point(0, 0);
    Point p2=new Point(1, 1);
    Point p3=new Point(2, 2);
    Triangle t1=new Triangle(p1, p1, p1);
    Triangle t2=t1;
    t1.show();
    System.out.println();//换行
    t1.area();
    t1.length();
    Scanner sc=new Scanner(System.in);
    System.out.println("请输入x，y：");
    x=sc.nextDouble();
    y=sc.nextDouble();
    p1.setX(x);
    p1.setY(y);
    t2.setA(p1);
    t2.setB(p2);
    t2.setC(p3);
    t2.show();
    System.out.println();
    t2.area();
    t2.length();  }
}

运行截图：