addActionListener

addActionListener is a method used in Java's AWT and Swing to register listeners that respond to action events. It is defined by components such as Button and AbstractButton (including JButton) as well as JMenuItem, and it accepts an ActionListener. The ActionListener interface declares one method, actionPerformed(ActionEvent e), which is invoked when the user activates the component (for example, by clicking a button or selecting a menu item) or when an action event is fired programmatically.

Typical usage involves providing an ActionListener implementation and adding it to the component: button.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { /* handle action */ } }); Modern Java allows a more concise form using lambdas: button.addActionListener(e -> { /* handle action */ });

Multiple listeners can be attached to a single component; they are notified in the order they were added. Listeners can be removed with removeActionListener(ActionListener l). The ActionEvent object provides details about the event, including the source, the action command, and the event timestamp.

Events generated by addActionListener are dispatched on the Event Dispatch Thread. Long-running tasks inside actionPerformed should be offloaded to background threads to keep the user interface responsive.

This mechanism embodies the observer pattern, allowing modular handling of user interactions. It is widely used across AWT and Swing components beyond buttons and menu items, enabling responsive UI behavior in desktop Java applications.