java - Java中引用的困惑

Question

我对这段代码感到困惑:

    public void setGraphicsColor(Colors colors) { 
      Graphics gc = bufferImage.getGraphics();
      switch(colors) {
      case BLACK:
          gc.setColor(Color.black);
          break;
      case DARK_GRAY:
          gc.setColor(Color.darkGray);
          break;
      case WHITE:
          gc.setColor(Color.white);
          break;
      default:
          break;
      };
}

gc 是否会引用 bufferImage 所具有的同一个 Graphics 对象？那么当gc设置颜色属性时，是改变本地副本还是改变bufferImage中的Graphics对象。根据我在网上读到的内容，它应该指的是实际对象而不是本地克隆。但是，当我调试此代码时，gc.setColor() 似乎没有对 bufferImage 执行任何操作。抱歉，如果这是一个愚蠢的问题。

编辑:更多背景

图形包装类MazePanel:

     public class MazePanel extends Panel  {
        /* Panel operates a double buffer see
         * http://www.codeproject.com/Articles/2136/Double-buffer-in-standard-Java-AWT
         * for details
         */
        Image bufferImage ;

        Color color;

        public enum Colors {
            BLACK, DARK_GRAY, WHITE
        };

        public MazePanel() {
            super() ;
            this.setFocusable(false) ;
        }
        @Override
        public void update(Graphics g) {
            paint(g) ;
        }
        @Override
        public void paint(Graphics g) {
            g.drawImage(bufferImage,0,0,null) ;
        }
        /*
        public void setBufferImage(Image buffer) {
            bufferImage = buffer ;
        }
        */
        public void initBufferImage() {
            bufferImage = createImage(Constants.VIEW_WIDTH, Constants.VIEW_HEIGHT);
            if (null == bufferImage)
            {
                System.out.println("Error: creation of buffered image failed, presumedly container not displayable");
            }
        }

        public Image getBufferImage() {
            return this.bufferImage;
        }

        public void setBufferImage(Image im) {
            this.bufferImage = im;
        }

        public Graphics getBufferImageGraphics() {
            if (null == bufferImage)
                initBufferImage() ;
            return bufferImage.getGraphics() ;
        }

        public void setGraphicsColor(Colors colors) { 
            Graphics gc = bufferImage.getGraphics();
            switch(colors) {
            case BLACK:
                gc.setColor(Color.black);
                break;
            case DARK_GRAY:
                gc.setColor(Color.darkGray);
                break;
            case WHITE:
                gc.setColor(Color.white);
                break;
            default:
                break;
            };
        }

        public void setGraphicsColor(Color color) {
            Graphics gc = bufferImage.getGraphics();
            gc.setColor(color);
        }

        public void setGraphicsColor(int r, int g, int b) {
            Graphics gc = bufferImage.getGraphics();
            Color color = new Color(r, g, b);
            gc.setColor(color);
        }

        public void fillGraphicsRect(int x, int y, int width, int height) {
            Graphics gc = bufferImage.getGraphics();
            gc.fillRect(x, y, width, height);
        }
        public void update() {
            paint(getGraphics()) ;
        }
}

这里正在使用包装器:(注释掉的代码有效)

 public void redraw(MazePanel mp, int state, int px, int py, int view_dx, int view_dy, int walk_step, int view_offset, RangeSet rset, int ang) {

        if (state != Constants.STATE_PLAY)
            return ;
        // new adjustment
//      this.gc = mp.getBufferImageGraphics() ;
        this.mazePanel.setBufferImage(mp.getBufferImage());
        this.rset = rset ;
        this.view_dx = view_dx ;
        this.view_dy = view_dy ;
        this.angle = ang ;

        // calculate view
        viewx = (px*map_unit+map_unit/2) + viewd_unscale(view_dx*(step_size*walk_step-view_offset));
        viewy = (py*map_unit+map_unit/2) + viewd_unscale(view_dy*(step_size*walk_step-view_offset));
        // update graphics
        // draw black background on lower half
//      gc.setColor(Color.black);
        mazePanel.setGraphicsColor(Colors.BLACK);
//      gc.fillRect(0, 0, view_width, view_height/2);
        mazePanel.fillGraphicsRect(0, 0, view_width, view_height/2);

Answer 1

我修好了!!!

我意识到调用 Graphics gc = bufferedImage.getGraphics() 每次都会返回不同的图形对象!。

因此，我在设置 bufferedImage 时设置图形，然后使用该实例!!!