action : Java Glossary

The Action interface in Swing is a glorified ActionListener. You typically extend AbstractAction and attach it to a JMenuItem to field its ActionEvents. You can use that same same Action to field ActionEvents from JButtons. If you do an Action.setEnabled( false ), that disables all the attached widgets in sync. The actionPerformed method of an individual Action can use getActionCommand to do a Hashtable lookup to find the code to execute. Alternatively, you can use the first character of the actionCommand as a case index. Alternatively, you can embed a binary 16-bit unsigned integer as the first character of an actionCommand and use that as an array index. Typically you use one Action per JMenuItem and redirect all (possibly predigested) ActionEvents to a common ActionListener for dispatching.

Why use Actions?

• You don’t need yet another inner class for every ActionListener, just another Action object. Inner classes have a 3K RAM (Random Access Memory) overhead each.
• You can use the same event handling logic for both a JButton and a JMenuItem. If you are going to have a menu item, a button on a UI (User Interface) screen and a button on a toolbar all do the same thing, you have one and only one method that they all call. There is no chance of them getting out of sync. You could do this without Actions by creating a common ActionListener, but now it is more convenient.
• You can enable or disable a collection of widgets that share a common Action with one call to action.setEnabled ( true ). You can change properties of all attached widgets with a single call, e.g.

  action.putValue( "ToolTipText", "Fermez le fichier" );

• Terser code. new JButton( Action ) or new JMenuItem( Action ) creates the JButton/JMenuItem, using properties in the Action (Text, Icon, Enabled, ToolTipText, ActionCommand and Mnemonic) and attaches the Action to the JButton/JMenuItem as an ActionListener and attaches the JButton/JMenuItem to the Action as a PropertyChangeListener.

• If you spell one of the properties incorrectly, the compiler won’t complain and neither will the runtime. Your property will just be ignored.
• Not all methods of JButton and JMenuItem are supported via Action. You will then have your logic split between the Action and the JButton/ JMenu.

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