更改一个对象改变所有这些

Question

我已创建类，较2-d点一类，和表示线段，其存储两个2 d点的类。但是，当我创建了三个单独的线段并在其中一个线段中更改值时，使用LineSegment类中的函数setStartPoint（Point2D arg），它会更改它们中的所有值。我假设这是因为我为每个LineSegment创建的所有对象都指向同一个对象，但是在我看来，我每次都声明一个新对象（使用new？）。如果有人能够发现我的错误，并指出我的方向正确，我将非常感激。

请注意，我只是需要一个例子来说明我做错了什么，我不想为我应该改变的代码行或者它在哪里的确切答案，只是想知道我是什么没有正确实施，就像我的计算机科学实验室一样。

驱动程序类，教授

public class driver 
{ 
    public static void lineSegmentDriver() 
    { 
     LineSegment a = new LineSegment(); 
     LineSegment b = new LineSegment(new Point2D(1,1), new Point2D(2,2)); 
     LineSegment c = new LineSegment(b); 

     a.setStartPoint(new Point2D(3,3)); 
     a.setEndPoint(new Point2D(4,4)); 

     System.out.println("Line a: " + a.toString()); 
     System.out.println("Line b: " + b.toString()); 
     System.out.println("Line c: " + c.toString()); 

     System.out.println("Line b's distance between points: " + b.distance()); 

     System.out.println("Does a equal b? " + a.equals(b)); 
     System.out.println("Does a equal c? " + a.equals(c)); 
     System.out.println("Does b equal c? " + b.equals(c)); 
    } 
} 

线段类，我写的书面（注释去掉）

public class LineSegment 
{ 
    private Point2D p1; 
    private Point2D p2; 

    public LineSegment() 
    { 
     this.p1 = new Point2D(0,0); 
     this.p2 = new Point2D(0,0); 
    } 
    public LineSegment(Point2D p1, Point2D p2) 
    { 
     if (p1 == null || p2 == null) 
     { 
      this.p1 = new Point2D(0,0); 
      this.p2 = new Point2D(0,0); 
     } 
     else 
     { 
      this.p1 = new Point2D(p1); 
      this.p2 = new Point2D(p2); 
     } 
    } 
    public LineSegment(LineSegment l) 
    { 
     this.p1 = new Point2D(l.p1); 
     this.p2 = new Point2D(l.p2); 
    } 

    public Point2D getStartPoint() 
    { 
     Point2D varRet = new Point2D(p1); 
     return varRet; 
    } 
    public void setStartPoint(Point2D arg) 
    { 
     this.p1 = new Point2D(arg); 
    } 

    public Point2D getEndPoint() 
    { 
     Point2D varRet = new Point2D(p2); 
     return varRet; 
    } 
    public void setEndPoint(Point2D arg) 
    { 
     this.p2 = new Point2D(arg); 
    } 

    public String toString() 
    { 
     return "Line start (" + this.p1.getX() + "," + this.p1.getY() + ") and end (" + 
      this.p2.getX() + "," + this.p2.getY() + ")"; 
    } 
    public boolean equals(Object o) 
    { 
     if (o instanceof LineSegment && o != null) 
     { 
      LineSegment toCompare = (LineSegment) o; 
      if (toCompare.p1.equals(this.p1) && 
       toCompare.p2.equals(this.p2)) 
        return true; 
     } 
     return false; 
    } 

    public double distance() 
    { 
     return Math.sqrt(((this.p1.getY() - this.p2.getY()) * (this.p1.getY() - this.p2.getY())) + 
         ((this.p2.getX() - this.p1.getX()) * (this.p1.getX() - this.p2.getX()))); 
    } 
} 

Point2D类，由我

public class Point2D 
{ 
    private static int x; 
    private static int y; 

    public Point2D() 
    { 
     this.x = -1; 
     this.y = -1; 
    } 
    public Point2D(int x, int y) 
    { 
     setX(x); 
     setY(y); 
    } 
    public Point2D(Point2D point) 
    { 
     setX(point.x); 
     setY(point.y); 
    } 

    public void setX(int x) 
    { 
     this.x = x; 
    } 
    public int getX() 
    { 
     return this.x; 
    } 

    public void setY(int y) 
    { 
     this.y = y; 
    } 
    public int getY() 
    { 
     return this.y; 
    } 

    public void resetToOrigin() 
    { 
     this.x = 0; 
     this.y = 0; 
    } 

    public void translate(int x, int y) 
    { 
     this.x += x; 
     this.y += y; 
    } 

    @Override 
    public String toString() 
    { 
     return Integer.toString(this.x) + "," + Integer.toString(this.y); 
    } 
    public boolean equals(Point2D pointObject) 
    { 
     if (this.x == pointObject.getX() && 
       this.y == pointObject.getY()) 
       return true; 
     return false; 
    } 

} 

写

Answer 1

问题是您已在您的Point2D中声明x和ystatic，这意味着当您更改它们时，它们将影响一般类而不是特定的Point2D实例。