ActionListener

ActionListener is an interface in the Java programming language, part of the AWT and Swing event models, used to receive action events fired by user interface components such as buttons and menu items. It defines a single method, actionPerformed(ActionEvent e). Implementations register with components using addActionListener; for example, a JButton can accept listeners that respond when the button is pressed. When the user activates the component, the component creates an ActionEvent and dispatches it to all registered listeners by invoking their actionPerformed methods.

ActionEvent, defined in java.awt.event, provides information about the event, including the event source, an action command string, and a timestamp. A single component may have multiple listeners registered, and listeners can be added or removed at runtime with addActionListener and removeActionListener.

ActionListener is a functional interface, so it can be implemented with a lambda expression in Java 8 and later, enabling concise event handling. For example, a lambda can be passed to addActionListener to perform a specific action when a button is clicked.

Best practices include keeping the event-handling code short and performing long-running tasks outside the Event Dispatch Thread. Time-consuming work should be delegated to background threads or SwingWorker to avoid freezing the user interface. ActionListener forms a core part of the standard Java event-handling model, supporting responsive, interactive GUI applications. See also EventListener, ActionEvent, JButton, and Swing components.