repaint为什么执行了两次？

Question

          int i; //记录重绘次数
          public void display(Shape shape,Ground ground){
System.out.println("GamePanel's display begin");
this.shape = shape;
this.ground = ground;
repaint();
System.out.println("GamePanel's display  end");
}
@Override
protected void paintComponent(Graphics g) {
// TODO Auto-generated method stub

if(shape !=null && ground != null){

System.out.println(i++);
shape.drawMe(); //此方法会打印Shape's drawMe
ground.drawMe(); //此方法会打印Ground's drawMe
}
}
打印结果：
GamePanel's display begin //第一次调用display
GamePanel's display begin
0
Shape's drawMe
Ground's drawMe
1
Shape's drawMe
Ground's drawMe
GamePanel's display begin //第二次调用display
GamePanel's display  end
2
Shape's drawMe
Ground's drawMe
GamePanel's display begin //第三次调用display
GamePanel's display  end
3
Shape's drawMe
Ground's drawMedisplay()是由其它类不停调用的，从打印结果里能看出，display里的repaint第一次调用的时候连续重绘了两次，以后就正常了，这是为什么呢？？

Answer 1

这个正常，因为paintComponent方法不光可被repaint触发，其他如初次布局、resize、窗口移动等因素都会触发paintComponent方法执行。

Answer 2

正如2楼说的，Swing会在很多时候，自动repaint的
楼主这里的现象是由于在componentShown事件时，
自动repaint引起的
看源码中的两段吧：        public void componentShown(ComponentEvent e) {
            if (shouldShow()) {
                synchronized (getTreeLock()) {
                    if (peer != null) {
                        peer.show();
                    }
                }
            }
        }
    public void show() {
        if (!visible) {
            synchronized (getTreeLock()) {
                visible = true;
                mixOnShowing();
                ComponentPeer peer = this.peer;
                if (peer != null) {
                    peer.show();
                    createHierarchyEvents(HierarchyEvent.HIERARCHY_CHANGED,
                                          this, parent,
                                          HierarchyEvent.SHOWING_CHANGED,
                                          Toolkit.enabledOnToolkit(AWTEvent.HIERARCHY_EVENT_MASK));
                    if (peer instanceof LightweightPeer) {
                        repaint();
                    }
                    updateCursorImmediately();
                }                if (componentListener != null ||
                    (eventMask & AWTEvent.COMPONENT_EVENT_MASK) != 0 ||
                    Toolkit.enabledOnToolkit(AWTEvent.COMPONENT_EVENT_MASK)) {
                    ComponentEvent e = new ComponentEvent(this,
                                                          ComponentEvent.COMPONENT_SHOWN);
                    Toolkit.getEventQueue().postEvent(e);
                }
            }
            Container parent = this.parent;
            if (parent != null) {
                parent.invalidate();
            }
        }
    }