JMenuItem
复选菜单项JCheckBoxMenuItem
上面两个必须加入到按钮组ButtonGroup()中
单选菜单项JRadioButtonMenuItem
弹出菜单JpopupMenu
show(c,x,y)
JPanel.setComponentPopupMenu()
快捷键
new JMenu("About",‘A’)
helpMenu.setMnemonic('H')
openItem.setAccedlerator(KeyStroke.getKeyStroke("ctrl 0"));
