该paintComponent方法实际上来自抽象类JComponent，它由类扩展，而类又是您要扩展的JPanel类。的实际实现paintComponent是：/** * Calls the UI delegate's paint method, if the UI delegate * is non-<code>null</code>. We pass the delegate a copy of the * <code>Graphics</code> object to protect the rest of the * paint code from irrevocable changes * (for example, <code>Graphics.translate</code>). * <p> * If you override this in a subclass you should not make permanent * changes to the passed in <code>Graphics</code>. For example, you * should not alter the clip <code>Rectangle</code> or modify the * transform. If you need to do these operations you may find it * easier to create a new <code>Graphics</code> from the passed in * <code>Graphics</code> and manipulate it. Further, if you do not * invoker super's implementation you must honor the opaque property, * that is * if this component is opaque, you must completely fill in the background * in a non-opaque color. If you do not honor the opaque property you * will likely see visual artifacts. * <p> * The passed in <code>Graphics</code> object might * have a transform other than the identify transform * installed on it. In this case, you might get * unexpected results if you cumulatively apply * another transform. * * @param g the <code>Graphics</code> object to protect * @see #paint * @see ComponentUI */protected void paintComponent(Graphics g) { if (ui != null) { Graphics scratchGraphics = (g == null) ? null : g.create(); try { ui.update(scratchGraphics, this); } finally { scratchGraphics.dispose(); } }}