绘制组件未根据预期坐标打印多边形

Question

我在根据存储在链接列表中的坐标绘制三角形多边形时遇到问题。当我在paint组件方法中使用System.out.println检查链表元素时，

Public void paintComponent (Graphics g)  {
...
   for (Polygon p : triangles) {
      g2.drawPolygon(triangle); 
      ... // print the elements of triangles
      System.out.println(p.xpoints[0]);
      System.out.println(p.xpoints[1]);
      System.out.println(p.xpoints[2]);
   }
}

它与读入的链表元素不相似，

public void getTriangles (){
   .....
   while (overlap) 
   {
    ...
   }

   for (Polygon p: triangles){
      ... //print the elements of triangles
      System.out.println(p.xpoints[0]);
      System.out.println(p.xpoints[1]);
      System.out.println(p.xpoints[2]);
   } 
}

我想知道为什么会发生这种情况。例如，在 public getTriangles 方法中读取的链表三角形中的 x 点为 x[0]= 379、x[0]= 429、x[2]= 404，并且在 paintComponent(Graphics g)x[0]= 249、x[0]= 299、x[2]= 274

   public class patternGenerator extends JPanel {
       private int n = 10;
       private int[] xCoord = new int[100];
       private int[] yCoord = new int[100]; 

       private List<Polygon> triangles = new LinkedList<Polygon>(); 

       public patternGenerator ()  {
       ....
       getTriangles();
       }

       public void getTriangles (){
          boolean overlap = true; //overlap


          /* This LOOP check for overlapping triangle. 
           * It will erase previous elements in linked list which are overlapping.
           * The triangles will only be painted when there is no overlapping triangles
           */
          while(overlap) {
             int MAX_WIDTH  = 600; 
             int MAX_HEIGHT = 600;
             int sizeCombination2a [] = {10,20};

             //remove previous drawn triangles
             if(triangles.size()>1) {
                Polygon[] triArray = triangles.toArray(new Polygon[triangles.size()]);
                for (Polygon p:triArray)  
                   triangles.remove (p);
             }

            //create new triangles
            for(int i = 0; i < numTriangles; i++) { //generate 10 triangles {

               int xWidth = sizeCombination2a[generator.nextInt(sizeCombination2a.length)]
               int yHeight= sizeCombination2a[generator.nextInt(sizeCombination2a.length)];

               xCoord[0] = generator.nextInt(MAX_WIDTH);
               xCoord[1] = (int) (xCoord[0] - xWidth);
               xCoord[2] = (int) (xCoord[1] + (xWidth/2));

               yCoord[0] = generator.nextInt(MAX_WIDTH);    
               yCoord[1] = yCoord[0];
               yCoord[2] = (int) (yCoord[1] - yHeight);  

               triangles.add( new Polygon(xCoord,yCoord, 3)); 
            }
            boolean results = checkOverlapAxis(aesParameter,aesLevel);

            if(results)
               overlap = false;

        }//end while (overlap)
     }

     public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g; 
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setStroke(new BasicStroke(1)); // set the thickness of polygon line
        g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1.00f));
        g2.setPaint(Color.black);//set the polygon line 

        for (Polygon triangle : triangles)
           g2.drawPolygon(triangle);

     }//end Paint
 }

Answer 1

这可能是线程问题。确保使用此三角形变量的所有活动都是同步的。

更好的是，将三角形变量的所有活动（设置、获取和绘制）限制在事件调度线程中，如下所示：

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        patternGenerator.setTriangles(...);
   }
}

Answer 2

最后我通过将 LIST 声明为以下方式解决了这个问题：

public static List<Polygon> triangles = new LinkedList<Polygon>();