Why listeners in java

Dashboard Logout. ActionListener This interface is used for receiving the action events. ComponentListener This interface is used for receiving the component events. ItemListener This interface is used for receiving the item events. KeyListener This interface is used for receiving the key events. Share Flipboard Email. Paul Leahy. Computer Science Expert. Paul Leahy is a computer programmer with over a decade of experience working in the IT industry, as both an in-house and vendor-based developer.

Updated February 18, Featured Video. Cite this Article Format. Leahy, Paul. Understanding and Processing Keyboard Events in Delphi. Placing Delphi Applications in the System Tray. Benefits of the Graphical User Interface. KeyListener This interface is used for receiving the key events.

MouseListener This interface is used for receiving the mouse events. WindowListener This interface is used for receiving the window events. AdjustmentListener This interface is used for receiving the adjustment events. ContainerListener This interface is used for receiving the container events.

Event Consumers The following event consumers can be set for an execution listener: OnEnter : An event that is notified when an execution of an element is entered.

This event is consumed before any input values are executed. OnReturn : An event that is notified when an execution of an element was entered and completed. At least one event consumer needs to be set otherwise an IllegalArgumentException will be thrown by the builder when it is attached.

Event consumers may throw any Java host exception. Such exceptions will be reported to the context as PolyglotException instances. The thrown exception may be accessed using PolyglotException. Event Data For every event that is consumed the source location and root name data is available. Other event data will return null by default. The collection of the following event data may be enabled: Return values : Enables access to return values in OnReturn events.

Input values : Enables access to input values in OnReturn events. Errors : Enables access to errors in OnReturn events. If additional event data is collected then the peak performance overhead of execution listeners is significant. It is not recommended to collect additional event data when running production workloads.