Introduction
Event handling in Java can be considered a paradigm in the interface that enables a listener in your applications and triggers responses based on the input received.
So what is an event? An event could be a specific user action, such as pressing a key or clicking the mouse. Now when any of these specified actions take place, a set of pre-determined, pre-programmed actions will set into course. Event handling is used by programmers and developers to make the code more interactive and to optimize and, to a certain degree, even customize user experiences.
To understand the components of event handling in Java, you must focus on three aspects. They are the event source, the event handler, and the event listener. They are tasked with generating, capturing, and executing the set of codes when the event happens, respectively.
Components of Event Handling in Java
1. Event Handler
Event handlers are responsible for defining the actions or behaviors that should occur in response to specific events. They contain the implementation code that handles the event and performs the desired tasks. Event handlers are typically implemented as methods within a class. When an event occurs, the associated event handler is invoked to respond to that event.
2. Event Sources
Event sources are objects that generate events. They are the entities or components that trigger events when specific actions or conditions occur. Examples of event sources include buttons, text fields, mouse clicks, or keyboard inputs. Event sources are responsible for creating and dispatching the corresponding event objects when the specific event occurs.
3. Event Listeners
Event listeners are interfaces or classes that define the methods to handle events. They are responsible for listening to events generated by event sources and invoking the appropriate event handlers to respond to those events. Event listeners implement the methods defined in the listener interface, which contain the logic for handling the events. Event listeners are registered with the event sources to receive and process the events.
Java Event Classes and Listener Interfaces
i) Event Classes
ActionEvent: This represents the user’s action, such as clicking a button or selecting a menu item.
MouseEvent: Represents mouse-related events, such as mouse clicks, movement, or dragging.
KeyEvent: Represents keyboard-related events, such as key presses or key releases.
WindowEvent: Represents events related to windows or frames, such as window opening, closing, or resizing.
FocusEvent: Represents events related to focus, such as when a component gains or loses focus.
ii) Listener Interfaces
ActionListener: Defines methods to handle ActionEvents.
MouseListener: Defines methods to handle MouseEvent.
MouseMotionListener: Defines methods to handle mouse motion events.
KeyListener: Defines methods to handle KeyEvent.
WindowListener: Defines methods to handle WindowEvent.
FocusListener: Defines methods to handle FocusEvent.
Steps to Perform Event Handling in Java
Here are the steps to perform event handling in Java:
Identify the event source: Determine which component or object will generate the events you want to handle. Event sources include buttons, text fields, or mouse clicks.
Implement the event listener interface: Create a class that implements the appropriate event listener interface. This interface defines the methods that will handle the events generated by the event source.
Implement event handling logic: Write the necessary code inside the event listener methods to specify the actions or behaviors that should occur when the events are triggered. This code will be executed when the events occur.
Register the event listener: Use the registration methods provided by the event source to register your event listener with the event source. This step establishes the connection between the event source and the event listener, allowing the listener to receive and handle the events generated by the source.
Perform event handling operations: Once the event listener is registered with the event source, it will receive events from the source. When an event occurs, the corresponding event handling method in the listener will be invoked, and you can perform the desired operations or actions based on the event.
Registration Methods
The specific registration methods can vary depending on the event source and the event listener interface being used. Some common registration methods include addActionListener(), addMouseListener(), or addKeyListener(). The event source class provides these methods and allow you to register the appropriate event listener for the specific event type.
Java Event Handling Code
1. Within class
import java.util.Scanner;
public class xx
{
public static void main(String[] args)
{
xx eevvnntt = new xx();
eevvnntt.see();
}
public void see() {
Scanner scanner = new Scanner(System.in);
System.out.println(“Enter a number: “);
int number = scanner.nextInt();
// Event handling logic
if (number % 2 == 0) {
System.out.println(number + ” is even.”);
} else {
System.out.println(number + ” is odd.”);
}
scanner.close();
}
}
This program prompts the user to enter a number and performs event handling logic to determine if the number is even or odd. The event handling logic is implemented within the same class where the main method resides. The program uses a Scanner object to read user input and performs the necessary calculations based on the input.
2. Outer class
import java.util.Scanner;
public class ww {
public static void main(String[] args) {
ss s = new ss();
s.dothis();
}
}
class ss {
public void dothis()
{
Scanner scanner = new Scanner(System.in);
System.out.println(“Enter your name: “);
String name = scanner.nextLine();
System.out.println(“Hello, ” + name + “! Welcome to the event handling program.”);
scanner.close();
}
}
This program prompts the user to enter their name and displays a welcome message.
The event handling logic is implemented in a separate outer class. The program uses a Scanner object to read user input and displays the welcome message based on the input.
Classification of Events
Foreground Events
Foreground events are user-triggered events that require immediate attention and interaction. These events are associated with user actions such as button clicks, menu selections, mouse movements, or keystrokes. The program actively listens and responds to these events in real time. Examples of foreground events include clicking a button, pressing a key, or selecting an item from a menu.
Background Events
Background events are system-triggered events that occur without direct user interaction.
These events typically occur in the background without the user’s immediate attention. The program may respond to these events periodically or as needed. Examples of background events include timers, network events, file system events, or system notification
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