Re: Button event

Knute Johnson <>
Thu, 29 Jun 2006 07:58:19 -0700
jaap wrote:

Ian Wilson schreef:

IchBin wrote:

jaap wrote:

I'm a real noob with java. I worked for 4 years with php but now I
have to use java.
I'm looking for a clean way to get an action behind a
button/menuitem. I already found the class actionListener. but the
method actionpreformed is not very clean if you want to give 20
buttons an action. The way I know is 20 times else if. There must be
an better method.

With you program just implement an ActionListener. After this you
have to add the required actionPerformed method. Then just check for
which buttons were selected. Here is an example code for buttons
objects. Naturally this is not a complete program but just info you
were asking about

public class MyButtons implements ActionListener
    private JButton deleteButton;
    private JButton reloadButton;
    private JButton returnButton;
    private JButton commitButton;

    private final String TEXT_DETELE = "Delete";
    private final String TEXT_RELOAD = "Reload";
    private final String TEXT_RETURN = "Return";
    private final String TEXT_COMMIT = "Commit";

    private final String _Click = "Click this
button to ";
    private final String _toolTipDelete = this._Click +
"Deleteed Se;ected quote from Database";
    private final String _toolTipReload = this._Click +
"Reload all remaintng dupicate Quotes from Database";
    private final String _toolTipReturn = this._Click +
"Return Insert Quotes";
    private final String _toolTipCommit = this._Click +
"Commit all Delete's to Database";

     public MyButtons ()
      deleteButton = buildButton (deleteButton, TEXT_DETELE,
KeyEvent.VK_D, _toolTipDelete));
      reloadButton = buildButton (reloadButton, TEXT_RELOAD,
KeyEvent.VK_R, _toolTipReload));
      returnButton = buildButton (returnButton, TEXT_RETURN,
KeyEvent.VK_X, _toolTipReturn));
      commitButton = buildButton (commitButton, TEXT_COMMIT,
KeyEvent.VK_C, _toolTipCommit));

    private JButton buildButton (JButton jButton, String label, int
keyEvent, String toolTip)
        jButton = new JButton(label);
        jButton.setMnemonic (keyEvent);
        jButton.addActionListener (this);
        jButton.setActionCommand (label);
        jButton.setToolTipText (toolTip);
        return jButton;
    public void actionPerformed (ActionEvent e)
        if (this.TEXT_RETURN.equals (e.getActionCommand ()))
        else if (this.TEXT_DETELE.equals (e.getActionCommand ()))
            else if (this.TEXT_RELOAD.equals (e.getActionCommand ()))
                else if (this.TEXT_COMMIT.equals (e.getActionCommand


It's a bit rude of me, a mere beginner in Java, to offer comments on
IchBin's contribution, so please accept my apologies for doing so:

In this specific example, you don't need to prefix the constants
"TEXT_RETURN" etc with "this.".

Eclipse also lays out (Ctrl-Shift-F) the if statement more like a case
statement, I prefer this layout:
   public void actionPerformed(ActionEvent e) {
        if (TEXT_RETURN.equals(e.getActionCommand())) {
            // do something
        } else if (TEXT_DELETE.equals(e.getActionCommand())) {
            // do something
        } else if (TEXT_RELOAD.equals(e.getActionCommand())) {
            // do something
        } else if (TEXT_COMMIT.equals(e.getActionCommand())) {
            // do something

I would also add some defensive code:
        } else {
            System.out.println("Internal error: command '"
                + e.getActionCOmmand() + "' unknown!";
            // or JOptionPane etc

Lastly: I feel impelled to insert `String command =
e.getActionCommand` at the top of the method and then change all
subsequent 'e.getActionCommand()' to 'command'. An old compulsion to
avoid 'expensive' subroutine calls from my Fortran IV days. Not that I
worry about microseconds nowadays - its just a habit :-)

Just my GBP 0.02 worth.

why I shouldn't use the way like java sun sugests? They create classes
for each action. You will get lots of classes but that won't be a
problem I sugest, am I wrong?

There is a lot of memory overhead for each internal class. The single
ActionListener with the if-else tests is the way to go if you have a lot
different events.

For the others:

public void actionPerformed(ActionEvent ae) {
     String ac = ae.getActionCommand();
     if (ac.equals("???")) {
     } else if(ac.equals("????")) {

saves a lot of calls to ActionEvent.getActionCommand() that are not


Knute Johnson
email s/nospam/knute/

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