?怎么有这个错误 Exception in thread "main" java.lang.Error: Do not use Chat.add() use Chat.getCo ntentPane().add() instead at javax.swing.JFrame.createRootPaneException(JFrame.java:465) at javax.swing.JFrame.addImpl(JFrame.java:491) at java.awt.Container.add(Container.java:518) at Chat.main(Chat.java:25) Press any key to continue...