JFrame默认关闭操作中可能有故障

Question

I'm experiencing a few issues with the JFrame's DefaultCloseOperation. I'm using Netbeans. I have set the close operation to custom code in the properties window of JFrame. Whenever I run this JFrame,the custom code executes automatically.Even if I dont close the frame.The custom code is basically a function:

public static int logout(){

   int userconfirm=  JOptionPane.showConfirmDialog(null,"Are you sure you want 
             to Exit?","Please Confirm",YES_NO_OPTION);
   if(userconfirm==0){
       return 1;
   }
   else 
      return 0;
   }

I dont know what int value must be returned for closing the frame,I'm just experimenting,so I return a zero or a one.

Answer 1

if(userconfirm==0){

First of all, don't use magic numbers. People don't know what "0" means. The API provides variables like JOptionPane.YES_OPTION that you can use. Use the variable provided by the API to make the code more readable.

Whenever I run this JFrame,the custom code executes automatically.Even if I dont close the frame

You should be using a WindowListener to monitor the closing of the window. The basic logic would be something like:

JFrame frame = new JFrame(...);
frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

frame.addWindowListener( new WindowAdapter()
{
    public void windowClosing(WindowEvent e)
    {
        JFrame frame = (JFrame)e.getSource();

        int result = JOptionPane.showConfirmDialog(
            frame,
            "Are you sure you want to exit the application?",
            "Exit Application",
            JOptionPane.YES_NO_OPTION);

        if (result == JOptionPane.YES_OPTION)
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
});

frame.setVisible( true );

Note: there is no need for a method as the closing logic is all handled inside the listener.

See Closing an Application for more information and coding ideas.