What is a JAVA event?

For example, let’s say we have a JButton (a button in Java with which the user can trigger an action). If a user clicks the JButton , a button click event is fired , which will be created and sent to the corresponding event listener (in this case ,  ActionListener). The relevant listener will have implemented the code that determines the action to perform when the event occurs.

Note that an event source has to be paired with an updated event listener, or triggering it will not result in any action.

How events work

To handle events correctly in Java, two fundamental elements must be known: the source and the listener of the event.

The object that is created when an event occurs is called the event source . The listener , on the other hand, is the object in charge of receiving the events and processing them at the moment they occur . It is important to note that Java provides several types of sources.

There are also several types of events and listeners in Java. Each type of event is directly configured or bound to a specific listener. For example, a common type of event are action events, represented by the ActionEvent Java class, which are fired when the user clicks a button or an item in a list.

In the user actions an object corresponding to the ActionEvent class is then created, which in turn corresponds to the relevant action. At that time, this object contains all the event source information and the specific action that the user has taken. This event object then transits to the object’s method of the corresponding ActionListener, that is, the corresponding listener.

empty action

When this procedure is executed, the appropriate GUI response is returned. It could be to open or close a dialog, make a digital signature, download files, or any of the many other actions that are available to a user in an interface.

Event Types

Below we list and explain some of the most common event types in Java:

• ActionEvent : Represents the action when a graphical element, such as a button or list item, is clicked. Related listener: ActionListener.
• ContainerEvent – ​​Represents an event that occurs in the GUI container itself, for example, if a user adds or removes an object from the interface. Related listener: ContainerListener .
• KeyEvent – ​​Represents an event where the user presses, types, or releases a key. Related listener: KeyListener .
• WindowEvent : represents any event related to a window, for example, when a window is closed and it is activated or deactivated. Related listener: WindowListener .
• MouseEvent – ​​Represents any event related to a mouse, such as click, double-click, etc. Related listener: MouseListener .

It is important to note that multiple listeners and event sources are capable of interacting with each other. For example, a single listener can register several events, if they are of the same type. This means that for a similar set of components that perform the same type of action, one event listener could handle them all. Similarly, a single event can be bound to multiple listeners, if that suits the design of the program, although this is much less common.

References

• Bell, B. (2003). JAVA for students. Available at: https://books.google.co.ve/books?id=TRUdyfwdaSoC&dq
• Harvey, M. (2003). How to program in Java. Available at: https://books.google.co.ve/books?id=is2J44U4DpsC&dq