#Java Events Examples Full And Cannot#
#Java Events Examples Code That Is#

Java Events Examples Code That Is

When such the event happens, the listener that is interested in that ActionEvent, which is called ActionListener, contains the method (called ' handler') to be invoked. For example, if we want to do something when a user clicks a button, then we need to identify 3 things: (1) the button itself, (2) the event when the button is clicked, and (3) the responding code that is interested in the button-clicked event (called 'listener').In java, the event when the button is clicked is called ActionEvent. The program decides either to ignore or to respond to when such cases happen. * Note: updated new source-code (SpeedEvent does NOT need to extend EventObject, my fault!)* If you are already familiar with standard Java GUI event-listener pair, you might skip this and go to Define custom source, event and listener.With Java (especially GUI) programs, the user might interact with a button, checkbox, car, or bank account.

For example, Java has provided standard models:- A JCheckBox can fire both ActionEvent and ItemEvent when the user checks or un-checks the checkbox. Also, a listener can declare one or multiple handlers. It was possible because the ActionListener had been registered to 'listen' to the ActionEvent by the button.The Event-Driving Programming Model in Java consists of 3 type objects:The source object (a JCheckbox, for example) fires an event object (of type ItemEvent, for example) when the user checks or un-checks the checkbox.The event object contains information about its source object.The listener object is an interface that must be registered as a 'listener' by the source object to be able to respond when the event object was fired, and invoke the the handler method of the listener object.* Note: a source object can fire one or multiple events, and one or multiple listeners can be registered by a source object.

This is not possible with pre-defined Java event-listener pairs.When defining our own event-listener pair, we should definitely follow the naming convention:XEvent - XListener (where X can be 'Action', 'Mouse', 'Account', 'Balance', 'Speed', etc.) Custom XEvent// or more flexible, the Source should maintain a list (collection) of XListeners // The Source must have code to register/de-register the XListener void addXListener(XListener myListener)// code to add myListener to the list of XListeners // the same for removeXListener method // When a condition happens, source object fires the eventXEvent myEvent = new XEvent( this, param1, param2.)// 'this' is the source object that fires myEvent // param1, param2. That means the BalanceEvent contains the data needed for the handler. For our custom BalanceListener's handler balanceViolated(BalanceEvent e) responds appropriately, it should be able to know how much the current balance is, the minimum amount that the account holder to maintain, and the date and time of that attempted transaction. For example, a bank account can fire a custom event BalanceEvent when the customer widthraws too much from his/her account. But we want to define our own because it is better suited with our application. Corresponding listener interface is MouseLister (which defines several handlers, such as mousePressed(MouseEvent e), and mouseEntered(MouseEvent e)), and KeyListener (with pre-defined handlers).Java has already provided many standard components with event-listener pair.

Java Events Examples Full And Cannot

For example, informing the client code the current balance, attempted ammount to widraw on what date. Since we pass the XEvent object to these handler(s), the handler(s) can respond appropriately. When a certain condition happends (such as low balance on the bank account, or a biology class is full and cannot take more students), the source object invokes the handler(s) method on its listeners.