Prompting the user whether to close the JFrame

[Jon Camilleri]

I would like to know how to add an event that prompts the user whether I can add an event handler for asking the user to confirm whether the program will exit when they select the [x] icon.

import javax.swing.*;
import javax.swing.filechooser.*;
import java.awt.*;

/**
* @version 0.1
* @author Jon C.
*/

public class ChooserTest
{
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame frm = new MyFrame();
				frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frm.setVisible(true);
			}
		});
	}

}

class MyFrame extends JFrame
{
	public MyFrame ()
	{
		setTitle("My Frame");
		setSize(300,200);
		JPanel panel = new JPanel(new BorderLayout());
		add(panel, BorderLayout.SOUTH);

		//draw a TextArea
		TextArea ta = new TextArea();
		ta.setColumns(20);
		ta.setRows(10);
		panel.add (ta);
	}

}

[Rob Spoor]

Set the default close operation to JFrame.DO_NOTHING, then use a WindowListener and listen for the windowClosing event. To close the frame now all you need to do is call dispose() on the frame. So:

public void windowClosing(WindowEvent e)
{
    JFrame frame = (JFrame)e.getWindow();
    if (canClose(frame)) // you define canClose
    {
        frame.dispose();
    }
    else
    {
        // other stuff
    }
}

[Jon Camilleri]

Rob Spoor wrote:Set the default close operation to JFrame.DO_NOTHING, then use a WindowListener and listen for the windowClosing event. To close the frame now all you need to do is call dispose() on the frame. So:

public void windowClosing(WindowEvent e)
{
    JFrame frame = (JFrame)e.getWindow();
    if (canClose(frame)) // you define canClose
    {
        frame.dispose();
    }
    else
    {
        // other stuff
    }
}

It's a pretty good hint, however I got a few questions:

1. For the sake of consistency I would like to declare all menuItems within MyFrame as private variables, but that would render my UI rendering quite
complex and hardcoded. I guess I'd rather have classes which generate menu items. Do you think that making menu items more readable by declaring them as
private members of JFrame is better programming practice, or else should I sub-class each and every menu item (which sounds too gory)?
2. I think I got a few compilation errors and my listeners incorrect however, this article will probably be helpful. Any hints?

import javax.swing.*;
import javax.swing.filechooser.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;

/**
* @version 1.0.0.1
* @author Jon C.
*/

public class ChooserTest
{
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame frm = new MyFrame();
				frm.setDefaultCloseOperation(JFrame.DO_NOTHING);
				frm.setVisible(true);
			}
		});
	}

}

class MyFrame 	extends JFrame
				implements WindowListener
{
	public MyFrame ()
	{
		final short WIDTH = 500;
		final short HEIGHT = 500;
		setTitle("Frame One");
		setSize(WIDTH,HEIGHT);

		panel = new JPanel(new BorderLayout());
		add(panel, BorderLayout.CENTER);

		//show File menu which includes an option to Open a text file
		JMenuBar menubar = new JMenuBar();
		setJMenuBar(menubar);
		filemenu = new JMenu("File");
		menubar.add(filemenu);

		JMenuItem openmenu = new JMenuItem("Open", 'O');
		openmenu.setAccelerator(Keystroke.getKeyStroke("ctrl O")); //BUG? What's wrong here?
		filemenu.add(openmenu);

		//draw a TextArea
		textarea = new TextArea();
		textarea.setColumns(20);
		textarea.setRows(10);
		panel.add(textarea);

		openmenu.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent event)
			{
				JFileChooser chooser = new JFileChooser();
				FileNameExtensionFilter filter = new FileNameExtensionFilter("Text Files", "txt");
				chooser.setFileFilter(filter);
				int returnVal = chooser.showOpenDialog(MyFrame.this);
				if(returnVal == JFileChooser.APPROVE_OPTION)
				{
					System.out.println("DEBUG: You chose to open this file: " + chooser.getSelectedFile().getName());
					textarea.setText(readTextFile(chooser.getSelectedFile()));
				}

			}
		});


	}

	private String readTextFile (File aFile)
	{
		//System.out.println("DEBUG: filename = " + filename);
		StringBuilder sb = new StringBuilder();
		try
		{
			Scanner in = new Scanner(aFile);
			in.useDelimiter("\n");
			while (in.hasNext())
			{
				sb.append(in.next());
			}

			in.close();

		}
		catch (FileNotFoundException e)
		{
			System.out.println("DEBUG: " + e.getMessage());
		}
		finally
		{
			return sb.toString();
		}

	}


	private void windowActivated(WindowEvent e) {}
	private void windowClosing(WindowEvent e)
	{

		    int choice = JOptionPane.showConfirmDialog(MyFrame.this, "Are you sure you want to exit?","", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
		    if (choice == JOptionPane.YES_OPTION)
		    {
		        MyFrame.this.dispose(); //is this correct?
		    }

    }
    private void windowClosed(WindowEvent e) {}
    private void windowDeactivated(WindowEvent e) {}
    private void windowDeiconified(WindowEvent e) {}
    private void windowIconified(WindowEvent e) {}
    private void windowOpened(WindowEvent e) {}
}

Compilation errors...
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:22: cannot find symbol
symbol : variable DO_NOTHING
location: class javax.swing.JFrame
frm.setDefaultCloseOperation(JFrame.DO_NOTHING);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:119: windowDeactivated(java.awt.event.WindowEvent) in MyFrame cannot implement windowDeactivated(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowDeactivated(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:107: windowActivated(java.awt.event.WindowEvent) in MyFrame cannot implement windowActivated(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowActivated(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:120: windowDeiconified(java.awt.event.WindowEvent) in MyFrame cannot implement windowDeiconified(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowDeiconified(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:121: windowIconified(java.awt.event.WindowEvent) in MyFrame cannot implement windowIconified(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowIconified(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:118: windowClosed(java.awt.event.WindowEvent) in MyFrame cannot implement windowClosed(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowClosed(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:108: windowClosing(java.awt.event.WindowEvent) in MyFrame cannot implement windowClosing(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowClosing(WindowEvent e)
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:122: windowOpened(java.awt.event.WindowEvent) in MyFrame cannot implement windowOpened(java.awt.event.WindowEvent) in java.awt.event.WindowListener; attempting to assign weaker access privileges; was public
private void windowOpened(WindowEvent e) {}
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:40: cannot find symbol
symbol : variable panel
location: class MyFrame
panel = new JPanel(new BorderLayout());
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:41: cannot find symbol
symbol : variable panel
location: class MyFrame
add(panel, BorderLayout.CENTER);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:46: cannot find symbol
symbol : variable filemenu
location: class MyFrame
filemenu = new JMenu("File");
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:47: cannot find symbol
symbol : variable filemenu
location: class MyFrame
menubar.add(filemenu);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:50: cannot find symbol
symbol : variable Keystroke
location: class MyFrame
openmenu.setAccelerator(Keystroke.getKeyStroke("ctrl O"));
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:51: cannot find symbol
symbol : variable filemenu
location: class MyFrame
filemenu.add(openmenu);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:54: cannot find symbol
symbol : variable textarea
location: class MyFrame
textarea = new TextArea();
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:55: cannot find symbol
symbol : variable textarea
location: class MyFrame
textarea.setColumns(20);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:56: cannot find symbol
symbol : variable textarea
location: class MyFrame
textarea.setRows(10);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:57: cannot find symbol
symbol : variable textarea
location: class MyFrame
panel.add(textarea);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:57: cannot find symbol
symbol : variable panel
location: class MyFrame
panel.add(textarea);
^
C:\Documents and Settings\Jon\workspace\JavaDev\myCode Snippets\ChooserTest.java:70: cannot find symbol
symbol: variable textarea
textarea.setText(readTextFile(chooser.getSelectedFile()));
^
20 errors

Tool completed with exit code 1


So having reverted to version 1 , I'm wondering whether there is a workaround to enable inner classes to access the textarea object

class MyFrame extends JFrame
{
...
public MyFrame()
{
...
//draw a TextArea
textarea = new TextArea();
textarea.setColumns(20);
textarea.setRows(10);
panel.add(textarea);
openmenu.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent event)
			{
				JFileChooser chooser = new JFileChooser();
				FileNameExtensionFilter filter = new FileNameExtensionFilter("Text Files", "txt");
				chooser.setFileFilter(filter);
				int returnVal = chooser.showOpenDialog(MyFrame.this);
				if(returnVal == JFileChooser.APPROVE_OPTION)
				{
					System.out.println("DEBUG: You chose to open this file: " + chooser.getSelectedFile().getName());
					textarea.setText(readTextFile(chooser.getSelectedFile())); 
/*
I have to declare textarea as a private variable, however, this is inconsistent with the other menuitems, and, thus, I want the code to be more readable.
So do I declare every menuitem as a private class member ( which seems useless?), or, do I sub-class (ugly and unreadable code?)  
Is there some other way to access variables from within inner anonymous classes? 
*/
}

}
});

...
}
...
private TextArea textarea;
}

The complete code for version 1 follows:

import javax.swing.*;
import javax.swing.filechooser.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;

/**
* @version 1.0.0.1
* @author Jon C.
* Allows the user to open a text file as read only.
*/

public class ChooserTest
{
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame frm = new MyFrame();
				frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frm.setVisible(true);
			}
		});
	}

}

class MyFrame 	extends JFrame
{
	public MyFrame ()
	{
		final short WIDTH = 500;
		final short HEIGHT = 500;
		setTitle("Frame One");
		setSize(WIDTH,HEIGHT);

		JPanel panel = new JPanel(new BorderLayout());
		add(panel, BorderLayout.CENTER);

		//show File menu which includes an option to Open a text file
		JMenuBar menubar = new JMenuBar();
		setJMenuBar(menubar);
		JMenu filemenu = new JMenu("File");
		menubar.add(filemenu);

		JMenuItem openmenu = new JMenuItem("Open", 'O');
		//openmenu.setAccelerator(Keystroke.getKeyStroke("ctrl O")); //TODO: FIX
		filemenu.add(openmenu);

		//draw a TextArea
		textarea = new TextArea();
		textarea.setColumns(20);
		textarea.setRows(10);
		textarea.setEditable(false);
		panel.add(textarea);

		openmenu.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent event)
			{
				JFileChooser chooser = new JFileChooser();
				FileNameExtensionFilter filter = new FileNameExtensionFilter("Text Files", "txt");
				chooser.setFileFilter(filter);
				int returnVal = chooser.showOpenDialog(MyFrame.this);
				if(returnVal == JFileChooser.APPROVE_OPTION)
				{
					System.out.println("DEBUG: You chose to open this file: " + chooser.getSelectedFile().getName());
					textarea.setText(readTextFile(chooser.getSelectedFile()));
				}

			}
		});


	}

	private String readTextFile (File aFile)
	{
		//System.out.println("DEBUG: filename = " + filename);
		StringBuilder sb = new StringBuilder();
		try
		{
			Scanner in = new Scanner(aFile);
			in.useDelimiter("\n");
			while (in.hasNext())
			{
				sb.append(in.next());
			}

			in.close();

		}
		catch (FileNotFoundException e)
		{
			System.out.println("DEBUG: " + e.getMessage());
		}
		finally
		{
			return sb.toString();
		}

	}

	private TextArea textarea;
}

[Jesper de Jong]

It should be DO_NOTHING_ON_CLOSE instead of DO_NOTHING.

Also, you cannot make methods like windowDeactivated, windowActivated, windowDeiconified etc. private. They are declared as public in the interfaces that they come from, so they must be public in your class.

[Jon Camilleri]

Jesper de Jong wrote:It should be DO_NOTHING_ON_CLOSE instead of DO_NOTHING.

Also, you cannot make methods like windowDeactivated, windowActivated, windowDeiconified etc. private. They are declared as public in the interfaces that they come from, so they must be public in your class.

Oh ok, what about my other q's?

[Jon Camilleri]

Jesper de Jong wrote:It should be DO_NOTHING_ON_CLOSE instead of DO_NOTHING.

Also, you cannot make methods like windowDeactivated, windowActivated, windowDeiconified etc. private. They are declared as public in the interfaces that they come from, so they must be public in your class.

Thanks, how about my other questions (hoping someone will read them )

So far, I have a frame which won't close, what is wrong with my listening code?

import javax.swing.*;
import javax.swing.filechooser.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;

/**
* @version 1.0.0.1
* @author Jon C.
* Allows the user to open a text file as read only.
*/

public class ChooserTest
{
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame frm = new MyFrame();
				frm.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
				frm.setVisible(true);
			}
		});
	}

}

class MyFrame 	extends JFrame
				implements WindowListener
{
	public MyFrame ()
	{
		final short WIDTH = 300;
		final short HEIGHT = 300;
		setTitle("Frame One");
		setSize(WIDTH,HEIGHT);

		JPanel panel = new JPanel(new BorderLayout());
		add(panel, BorderLayout.CENTER);

		//show File menu which includes an option to Open a text file
		JMenuBar menubar = new JMenuBar();
		setJMenuBar(menubar);
		JMenu filemenu = new JMenu("File");
		menubar.add(filemenu);

		JMenuItem openmenu = new JMenuItem("Open", 'O');
		filemenu.add(openmenu);

		//draw a TextArea
		textarea = new TextArea();
		textarea.setColumns(20);
		textarea.setRows(10);
		textarea.setEditable(false);
		panel.add(textarea);

		openmenu.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent event)
			{
				JFileChooser chooser = new JFileChooser();
				FileNameExtensionFilter filter = new FileNameExtensionFilter("Text Files", "txt");
				chooser.setFileFilter(filter);
				int returnVal = chooser.showOpenDialog(MyFrame.this);
				if(returnVal == JFileChooser.APPROVE_OPTION)
				{
					System.out.println("DEBUG: You chose to open this file: " + chooser.getSelectedFile().getName());
					textarea.setText(readTextFile(chooser.getSelectedFile()));
				}

			}
		});
		addWindowListener(this); //?


	}

	private String readTextFile (File aFile)
	{
		//System.out.println("DEBUG: filename = " + filename);
		StringBuilder sb = new StringBuilder();
		try
		{
			Scanner in = new Scanner(aFile);
			in.useDelimiter("\n");
			while (in.hasNext())
			{
				sb.append(in.next());
			}

			in.close();

		}
		catch (FileNotFoundException e)
		{
			System.out.println("DEBUG: " + e.getMessage());
		}
		finally
		{
			return sb.toString();
		}

	}

	public void windowActivated (WindowEvent e) {}
	public void windowClosed (WindowEvent e)
	{
		int choice = JOptionPane.showConfirmDialog(MyFrame.this, "Are you sure you want to exit?","", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
		if (choice == JOptionPane.YES_OPTION)
		{
		    MyFrame.this.dispose();
        }
	}
	public void windowClosing (WindowEvent e) {}
	public void windowDeactivated (WindowEvent e) {}
	public void windowDeiconified (WindowEvent e) {}
	public void windowIconified (WindowEvent e) {}
	public void windowOpened (WindowEvent e) {}

	private TextArea textarea;
}

Related links:
1. How to write Window Listeners (Oracle)

[Jesper de Jong]

Move the code that you put in the windowClosed method to the windowClosing method.

As you can read in the documentation of interface WindowListener, windowClosed is called after dispose has been called on the window, and windowClosing is...

java.awt.event.WindowListener wrote:
Invoked when the user attempts to close the window from the window's system menu.

[Jon Camilleri]

Jesper de Jong wrote:Move the code that you put in the windowClosed method to the windowClosing method.

As you can read in the documentation of interface WindowListener, windowClosed is called after dispose has been called on the window, and windowClosing is...

java.awt.event.WindowListener wrote:
Invoked when the user attempts to close the window from the window's system menu.

Sorry, I should have seen that coming, now it works as expected

As a general design rule, do you suggest declaring the components (e.g. menuitems, textarea) within the JFrame as private variables, so that the code is more readable? This is because I had to declare TextArea as a private variable, so that the inner class within MyFrame would be able to access textarea.
Is there some nifty workaround to access variables of outer classes?

I think I need to research the implementation of the Keystroke as well to enable modfiers (such as Ctrl + O to access the openmenu), because Keystroke does not seem to document KEY_TYPED events.

import javax.swing.*;
import javax.swing.filechooser.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;

/**
* @version 1.0.0.1
* @author Jon C.
* Allows the user to open a text file as read only.
*
* Known issues
* 1. Will not close due to problem with WindowListener.
*/

public class ChooserTest
{
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				MyFrame frm = new MyFrame();
				frm.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
				frm.setVisible(true);
			}
		});
	}

}

class MyFrame 	extends JFrame
				implements WindowListener
{
	public MyFrame ()
	{
		final short WIDTH = 300;
		final short HEIGHT = 300;
		setTitle("Frame One");
		setSize(WIDTH,HEIGHT);

		JPanel panel = new JPanel(new BorderLayout());
		add(panel, BorderLayout.CENTER);

		//show File menu which includes an option to Open a text file
		JMenuBar menubar = new JMenuBar();
		setJMenuBar(menubar);
		JMenu filemenu = new JMenu("File");
		menubar.add(filemenu);

		JMenuItem openmenu = new JMenuItem("Open", 'O');
		filemenu.add(openmenu);

		//draw a TextArea
		textarea = new TextArea();
		textarea.setColumns(20);
		textarea.setRows(10);
		textarea.setEditable(false);
		panel.add(textarea);

		openmenu.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent event)
			{
				JFileChooser chooser = new JFileChooser();
				FileNameExtensionFilter filter = new FileNameExtensionFilter("Text Files", "txt");
				chooser.setFileFilter(filter);
				int returnVal = chooser.showOpenDialog(MyFrame.this);
				if(returnVal == JFileChooser.APPROVE_OPTION)
				{
					System.out.println("DEBUG: You chose to open this file: " + chooser.getSelectedFile().getName());
					textarea.setText(readTextFile(chooser.getSelectedFile()));
				}

			}
		});
		addWindowListener(this);


	}

	private String readTextFile (File aFile)
	{
		//System.out.println("DEBUG: filename = " + filename);
		StringBuilder sb = new StringBuilder();
		try
		{
			Scanner in = new Scanner(aFile);
			in.useDelimiter("\n");
			while (in.hasNext())
			{
				sb.append(in.next());
			}

			in.close();

		}
		catch (FileNotFoundException e)
		{
			System.out.println("DEBUG: " + e.getMessage());
		}
		finally
		{
			return sb.toString();
		}

	}

	public void windowActivated (WindowEvent e) {}
	public void windowClosed (WindowEvent e){}
	public void windowClosing (WindowEvent e)
	{
		int choice = JOptionPane.showConfirmDialog(MyFrame.this, "Are you sure you want to exit?","", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
				if (choice == JOptionPane.YES_OPTION)
				{
				    MyFrame.this.dispose();
        		}
	}
	public void windowDeactivated (WindowEvent e) {}
	public void windowDeiconified (WindowEvent e) {}
	public void windowIconified (WindowEvent e) {}
	public void windowOpened (WindowEvent e) {}

	private TextArea textarea;
}

[Rob Spoor]

Jesper de Jong wrote:It should be DO_NOTHING_ON_CLOSE instead of DO_NOTHING.

Right. My bad, I didn't look it up. All the closing constants end with _ON_CLOSE.