JAVA，setter没有得到发送给我的构造函数程序返回零的值

Question

我遇到的错误是控制台打印出点值中的所有零，当它应该显示类似于（1,2）（3,4）（5,6）（7,8）的东西时

我将错误跟踪到了setter，它没有加载值。例

 public void setPoint1(double newX, double newY) {
  this.N1x = newX;
  this.N1y = newY;

}

这不会将私有双N1.x更新为相应的构造函数值1.我相信这是问题，但我是新编码，仍然有很多东西要学习。

据我所知，构造函数中对setter的调用应该从构造函数调用中获取1到8个值，然后发送到setter，然后将它们分发到私有双精度，然后执行Point Class操作，值为保存到point1到point4对象，然后从main方法调用它们返回其存储的值。

以下是我对我的问题的代码。先感谢您！

public class Quadrilateral {

   //Receives data from constructor 
   //initializes the variables for point objects  
   private double N1x; private double N1y;
   private double N2x; private double N2y;
   private double N3x; private double N3y;
   private double N4x; private double N4y;

   //creates new point objects
   Point point1 = new Point(N1x,N1y);
   Point point2 = new Point(N2x,N2y);
   Point point3 = new Point(N3x,N3y);
   Point point4 = new Point(N4x,N4y);

   // Encapsulation for point 1
   public Point getPoint1() {
      return point1;
   }
   public void setPoint1(double newX, double newY) {
      this.N1x = newX;
      this.N1y = newY;
   }

   // Encapsulation for point 2
   public Point getPoint2() {
      return point2;
   }
   public void setPoint2(double newX, double newY) {
      this.N2x = newX;
      this.N2y = newY;
   }

   // Encapsulation for point 3
   public Point getPoint3() {
      return point3;
   }
   public void setPoint3(double newX, double newY) {
      this.N3x = newX;
      this.N3y = newY;
   }

   // Encapsulation for point 4
   public Point getPoint4() {
      return point4;
   }
   public void setPoint4(double newX, double newY) {
      this.N4x = newX;
      this.N4y = newY;
   }

   //constructor for Quadrilateral
   //takes in 4 sets of point values
   Quadrilateral(
         double N1x, double N1y,
         double N2x, double N2y,
         double N3x, double N3y,
         double N4x, double N4y){

      setPoint1(N1x, N1y);
      setPoint2(N2x, N2y);
      setPoint3(N3x, N3y);
      setPoint4(N4x, N4y);

   }

   // gets the (x,y) values 
   //remember to override to add additional values and change shape

   public String toString() {
      return "Quadrilateral "+"\n"+ 
            "Node points are "+"\n"+
            getPoint1()+"\n"+
            getPoint2()+"\n"+
            getPoint3()+"\n"+
            getPoint4();
   }

public static void main(String[] args) {

   Quadrilateral quadrilateral = new Quadrilateral(1,2,3,4,5,6,7,8);
   System.out.println(quadrilateral.toString());
   }

}

这是点类

public class Point {
   private double x;
   private double y;

   public double getX() {
      return x;
   }
   public double getY() {
      return y;
   }
   public void setX(double newX) {
      this.x = newX;
   }
   public void setY(double newY) {
      this.y= newY;
   }
   Point(double x, double y){//when this constructor is called it performs encapsulation 
      setX(x);
      setY(y);
   }
   public String toString() {
      return "("+getX()+","+getY()+")";
   }
}

Answer 1

如果我理解你的问题，你应该这样做：

//creates new point objects
Point point1;
Point point2;
Point point3;
Point point4;

还有这个：

public void setPoint1(double newX, double newY) {
    this.N1x = newX;
    this.N1y = newY;
    point1 = new Point(newX, newY);
}

（对于其他点制定者也是如此）

在您的代码中，您只在坐标为空时初始化点，然后才能在setPoint方法中首次设置坐标

Answer 2

由于初始化Point对象，即使在使用未初始化的N1x，N2x等调用构造函数之前，Quadrilateral的成员变量也会在Point对象（成员变量）中设置它们的默认值0。如下更改四边形类定义

public class Quadrilateral {

    // creates new point objects
    Point point1 ;
    Point point2;
    Point point3 ;
    Point point4 ;

    // Encapsulation for point 1
    public Point getPoint1() {
        return point1;
    }

    public void setPoint1(double newX, double newY) {
        this.point1 = new Point(newX, newY);        
    }

    // Encapsulation for point 2
    public Point getPoint2() {
        return point2;
    }

    public void setPoint2(double newX, double newY) {
        this.point2 = new Point(newX, newY);
    }

    // Encapsulation for point 3
    public Point getPoint3() {
        return point3;
    }

    public void setPoint3(double newX, double newY) {
        this.point3 = new Point(newX, newY);
    }

    // Encapsulation for point 4
    public Point getPoint4() {
        return point4;
    }

    public void setPoint4(double newX, double newY) {
        this.point4 = new Point(newX, newY);
    }

    // constructor for Quadrilateral
    // takes in 4 sets of point values
    Quadrilateral(double N1x, double N1y, double N2x, double N2y, double N3x, double N3y, double N4x, double N4y) {

        setPoint1(N1x, N1y);
        setPoint2(N2x, N2y);
        setPoint3(N3x, N3y);
        setPoint4(N4x, N4y);

    }

    // gets the (x,y) values
    // remember to override to add additional values and change shape

    public String toString() {
        return "Quadrilateral " + "\n" + "Node points are " + "\n" + getPoint1() + "\n" + getPoint2() + "\n"
                + getPoint3() + "\n" + getPoint4();
    }

    public static void main(String[] args) {

        Quadrilateral quadrilateral = new Quadrilateral(1, 2, 3, 4, 5, 6, 7, 8);
        System.out.println(quadrilateral.toString());
    }

}