一个windowcloing的问题

private void initialize() {
this.setSize(500, 350);
this.setContentPane(getJContentPane());
this.addWindowListener(new java.awt.event.WindowAdapter() {   
public void windowOpened(java.awt.event.WindowEvent e) {    
// TODO Auto-generated Event stub windowOpened()
Toolkit toolkit=Toolkit.getDefaultToolkit();
BaseFrame baseframe=((BaseFrame)(e.getSource()));
int x=(toolkit.getScreenSize().width-baseframe.getWidth())/2;
int y=(toolkit.getScreenSize().height-baseframe.getHeight())/2;
baseframe.setLocation(x,y);
}
public void windowClosing(java.awt.event.WindowEvent e) {
// TODO Auto-generated Event stub windowClosing()
if (JOptionPane.showConfirmDialog(null,"向导还未结束,你确定要离开这个程序吗?","关闭应用程序",JOptionPane.YES_NO_OPTION)==JOptionPane.YES_OPTION){
System.exit(0);
}
else{
return;
}
}
});
}
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我想窗口在关的时候提问YES和NO,如果点NO,窗口不关闭.但现在点NO后,窗口还是关了,程序未结束.程序是什么地方有问题呢?