How to get Variable Name of button on press?

Question

I have a problem with obtaining ID / Variable Name of buttons. Generally I want create lights out game. I created panel of buttons (NxN, N from combo box) but I don't know how to get single button's ID after press. Any idea?

    private void p1ActionPerformed(java.awt.event.ActionEvent evt) {                                             
    String temp = jComboBox1.getSelectedItem().toString();
    ile=Integer.parseInt(temp);

    jPanel1.removeAll();
    jPanel1.setLayout(new GridLayout(ile,ile));
    for (int i = 0; i < ile; i++) {
        for (int j = 0; j < ile; j++) {  
            JButton btn = new JButton();
            btn.setPreferredSize(new Dimension(40, 40));
            btn.setBackground(Color.green);
            btn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e)
            {          
        /*What put here?*/
            }
            });
            jPanel1.add(btn);  
            revalidate();
            pack();
        }
    }
}

maybe [getSource()](http://docs.oracle.com/javase/7/docs/api/java/util/EventObject.html#getSource()) is what you're looking for — J4v4, Aug 27 '14 at 11:49
In the current context, you can just use `btn`. Just make it `final` — Paul Samsotha, Aug 27 '14 at 11:56

Hovercraft Full Of Eels · Accepted Answer · 2014-08-27T12:05:29.110

You can get a reference to the button pushed through the ActionEvent's getSource() method.

e.g.,

public void actionPerformed(ActionEvent e)  {          
   JButton selectedButton = (JButton) e.getSource();
}

Now, if you need to know where the button is in your grid, you will need to do more work, such as putting your buttons into an array or ArrayList, and then iterating through the array finding the index number of the selected button.

e.g.,

// changes to code marked with a //!! comment
private void p1ActionPerformed(java.awt.event.ActionEvent evt) {
  String temp = jComboBox1.getSelectedItem().toString();
  ile = Integer.parseInt(temp);

  jPanel1.removeAll();
  jPanel1.setLayout(new GridLayout(ile, ile));

  final JButton[][] buttons = new JButton[ile][ile]; //!!

  for (int i = 0; i < ile; i++) {
     for (int j = 0; j < ile; j++) {
        JButton btn = new JButton();
        btn.setPreferredSize(new Dimension(40, 40));
        btn.setBackground(Color.green);
        btn.addActionListener(new ActionListener() {
           public void actionPerformed(ActionEvent e) {
              //!!
              JButton source = (JButton) e.getSource();
              for (int k = 0; k < buttons.length; k++) {
                 for (int l = 0; l < buttons[k].length; l++) {
                    if (buttons[k][l] == source) {
                       System.out.printf("row: %d, col: %d%n", l, k);
                       return;
                    }
                 }
              }
           }
        });
        jPanel1.add(btn);
        buttons[i][j] = btn; //!!
        //!! revalidate();
        //!! pack();
     }
  }
  jPanel1.revalidate(); //!!
  jPanel1.repaint(); //!!
}

As a side note, whenever I see removeAll() I think that perhaps this can be better achieved by using a CardLayout

As a second side note, I always cringe when I see "get variable name" in questions. Variable "names" aren't really all that important, don't exist for many objects, and almost don't exist in compiled code. And if an object is referred to by several variables, which one represents the "name" for this object? Much more important are object references, which is what most of the answers to your question have been dealing with.

@mKorbel Or `getName` or `getActionCommand` ... lots of options — MadProgrammer, Aug 27 '14 at 11:58
Yes, the key is to somehow grab the reference and make sense of it in a clean non-kludgy way. — Hovercraft Full Of Eels, Aug 27 '14 at 11:59

score 2 · Answer 2 · answered Aug 27 '14 at 11:56

The suggestion of Hovercraft Full Of Eels is good. Alternatively in your case you can use the button defined in your code, but you should make it final.

for (int i = 0; i < ile; i++) {
    for (int j = 0; j < ile; j++) {  
        final JButton btn = new JButton();
        btn.setPreferredSize(new Dimension(40, 40));
        btn.setBackground(Color.green);
        btn.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e)
        {          
           // here we can use the variable btn - java will create an access method automatically
           System.out.println(btn.getText());
        }
        });
        jPanel1.add(btn);  
        revalidate();
        pack();
    }
}

Yep, very true, clean and simple. 1+ – Hovercraft Full Of Eels Aug 27 '14 at 12:01 — Hovercraft Full Of Eels, Aug 27 '14 at 12:01

MadProgrammer · Answer 3 · 2014-08-27T12:10:17.897

You have a ton of options (as you can see).

You can also use set/getName and/or set/getActionCommand, even set/getText, but I personally wouldn't rely on this...

for (int i = 0; i < ile; i++) {
    for (int j = 0; j < ile; j++) {  
        JButton btn = new JButton();
        btn.setBackground(Color.green);
        String id = Integer.toString(i) + "x" + Integer.toString(j);
        btn.setName(id);
        // and/or
        btn.setActionCommand(id);
        btn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e)
            {          
                JButton btn = (JButton)e.getSource();
                String id = btn.getName();
                // and/or
                String id = btn.getActionCommand();
            }
        });
        jPanel1.add(btn);  
    }
}
pack();

@HovercraftFullOfEels Copy and paste, my bad - with the `pack`, I doubt it would be required at all — MadProgrammer, Aug 27 '14 at 12:09

How to get Variable Name of button on press?

3 Answers3