Java handler мы listener

What’s the difference between Event Listeners & Handlers in Java?

There’s no formally defined difference between listeners and handlers. Some people would probably argue that they are interchangeable. To me however, they have slightly different meaning.

A listener is an object that subscribes for events from a source. Cf. the observer pattern. Usually you can have many listeners subscribing for each type of event, and they are added through addXyzListener methods.

Example: The MouseListener in the Java API.

A handler is an object that is responsible for handling certain events. A typical scenario would be to provide a handler for a specific event/task as an argument to a constructor, or set the handler through a setXyzHandler method. In other words, you usually have one handler for each type of event.

Example: The MemoryHandler in the Java API.

The most basic difference is the association

• Listener is associated with Event Source (Ex: key board)
• Handler is associated with an Event (Ex: keydown)

Generally speaking, there will only one central Handler Manager which manages all the events, while in case of Listener each Entity which wants to listen, will have to manage their own Collection of listeners

A listener watches for an event to be fired. For example, a KeyListener waits for KeyEvents, a MessageListener waits for messages to arrive on a queue and so on.

The handler is responsible for dealing with the event. Normally, listeners and handlers go hand-in-hand. For example, the KeyListener tells the ExitHandler that «the letter Q was pressed» and the handler performs logic such as cleaning up resources and exiting the application gracefully. Similary a ButtonClickListener would tell the same ExitHandler that the «Exit button was clicked». So, in this case you have two different events, two different listeners but a single handler.

Источник

What’s the difference between Event Listeners & Handlers in Java?

When it comes to programming in Java, both Event Listeners and Handlers are used to handle events. However, there are some differences between these two concepts.

Event Listeners

An Event Listener is an object that waits for an event to occur, and then triggers an action in response. In other words, it listens for a particular event to happen and then responds to that event.

For example, the ActionListener interface is an event listener in Java that waits for the user to click a button and then performs a specific action. Here’s an example code snippet for an ActionListener:

JButton button = new JButton("Click me"); button.addActionListener(new ActionListener() < public void actionPerformed(ActionEvent e) < // Perform action when button is clicked System.out.println("Button clicked"); >>); 

In this example, the ActionListener waits for the button to be clicked and then performs the action specified in the actionPerformed method.

Handlers

A Handler, on the other hand, is a method that is called when a specific event occurs. It is responsible for handling the event and performing the necessary actions.

For example, the MouseAdapter class is a handler in Java that handles mouse events such as clicking, dragging, and releasing. Here’s an example code snippet for a MouseAdapter:

JPanel panel = new JPanel(); panel.addMouseListener(new MouseAdapter() < public void mouseClicked(MouseEvent e) < // Perform action when mouse is clicked on panel System.out.println("Mouse clicked on panel"); >>); 

In this example, the MouseAdapter waits for the mouse to be clicked on the panel and then performs the action specified in the mouseClicked method.

Conclusion

In summary, both Event Listeners and Handlers are used to handle events in Java, but they do so in different ways. Event Listeners wait for an event to occur and then respond to it, while Handlers are methods that are called when a specific event occurs. Understanding the difference between these two concepts is important for effective event handling in Java.

Источник

Java Event Handler — Events and Listeners Examples

A quick guide to event handlers in java. How to add events and listeners to the buttons, text fields, and for different actions of the keyboard.

1. Overview

When you are working on GUI based projects using AWT or Applets then you might have seen the scenarios where you need to change the state of an object from one form to another.

For example, add action when a button is pressed or when the text is entered then enable another text box.

2. Java Event classes and Interfaces

3. Steps to add Events and Listeners — Example

Implement actionPerformed() method. Inside this, we need to change the text field contents using textField.setText() method.

Add the action listener created to the button. You need to call the button.addActionListener() method and pass the instance of ActionListener implementation object.

This program first displays the window and a text field with the default text «Enter your name». This window is displayed with a button.

package com.javaprogramto.programs.events; import java.awt.Button; import java.awt.Frame; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class JaveEventHandlerExample < public static void main(String[] args) < new ButtonEvent(); >> class ButtonEvent extends Frame implements ActionListener < TextField textField; ButtonEvent() < textField = new TextField(); textField.setText("Enter your name"); textField.setBounds(70, 60, 180, 30); Button b = new Button("click me"); b.setBounds(110, 130, 90, 40); b.addActionListener(this); add(b); add(textField); setSize(300, 300); setLayout(null); setVisible(true); >public void actionPerformed(ActionEvent e) < textField.setText("hello developer"); >>

4. Adding Listener from Custom class

In the above example, creating and adding action listeners are done within the same class but now let us see how to separate the action listener. How to attach the action listener to the button.

class ActionEventListner implements ActionListener < ButtonEvent buttonEvent; public ActionEventListner(ButtonEvent buttonEvent) < this.buttonEvent = buttonEvent; >@Override public void actionPerformed(ActionEvent e) < buttonEvent.textField.setText("hello developer"); >>

Create the main class which extends Frame and pass the ActionEventListener object to the button of addActionListner() method.

import java.awt.Button; import java.awt.Frame; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class JaveEventHandlerExample2 < public static void main(String[] args) < new ButtonEvent(); >> class ButtonEvent extends Frame < TextField textField; ButtonEvent() < textField = new TextField(); textField.setText("Enter your name"); textField.setBounds(70, 60, 180, 30); Button b = new Button("click me"); b.setBounds(110, 130, 90, 40); b.addActionListener(new ActionEventListner(this)); add(b); add(textField); setSize(300, 300); setLayout(null); setVisible(true); >>

5. Conclusion

In this article, we’ve seen how to add the action listeners for an event in java using java event handler concept.

Labels:

SHARE:

About Us

Java 8 Tutorial

• Java 8 New Features
• Java 8 Examples Programs Before and After Lambda
• Java 8 Lambda Expressions (Complete Guide)
• Java 8 Lambda Expressions Rules and Examples
• Java 8 Accessing Variables from Lambda Expressions
• Java 8 Method References
• Java 8 Functional Interfaces
• Java 8 — Base64
• Java 8 Default and Static Methods In Interfaces
• Java 8 Optional
• Java 8 New Date Time API
• Java 8 — Nashorn JavaScript

Java Threads Tutorial

Kotlin Conversions

Kotlin Programs

Java Conversions

• Java 8 List To Map
• Java 8 String To Date
• Java 8 Array To List
• Java 8 List To Array
• Java 8 Any Primitive To String
• Java 8 Iterable To Stream
• Java 8 Stream To IntStream
• String To Lowercase
• InputStream To File
• Primitive Array To List
• Int To String Conversion
• String To ArrayList

Java String API

• charAt()
• chars() — Java 9
• codePointAt()
• codePointCount()
• codePoints() — Java 9
• compareTo()
• compareToIgnoreCase
• concat()
• contains()
• contentEquals()
• copyValueOf()
• describeConstable() — Java 12
• endsWith()
• equals()
• equalsIgnoreCase()
• format()
• getBytes()
• getChars()
• hashcode()
• indent() — Java 12
• indexOf()
• intern()
• isBlank() — java 11
• isEmpty()
• join()
• lastIndexOf()
• length()
• lines()
• matches()
• offsetByCodePoints()
• regionMatches()
• repeat()
• replaceFirst()
• replace()
• replaceAll()
• resolveConstantDesc()
• split()
• strip(), stripLeading(), stripTrailing()
• substring()
• toCharArray()
• toLowerCase()
• transform() — Java 12
• valueOf()

Spring Boot

$show=Java%20Programs

$show=Kotlin

accumulo,1,ActiveMQ,2,Adsense,1,API,37,ArrayList,18,Arrays,24,Bean Creation,3,Bean Scopes,1,BiConsumer,1,Blogger Tips,1,Books,1,C Programming,1,Collection,8,Collections,37,Collector,1,Command Line,1,Comparator,1,Compile Errors,1,Configurations,7,Constants,1,Control Statements,8,Conversions,6,Core Java,149,Corona India,1,Create,2,CSS,1,Date,3,Date Time API,38,Dictionary,1,Difference,2,Download,1,Eclipse,3,Efficiently,1,Error,1,Errors,1,Exceptions,8,Fast,1,Files,17,Float,1,Font,1,Form,1,Freshers,1,Function,3,Functional Interface,2,Garbage Collector,1,Generics,4,Git,9,Grant,1,Grep,1,HashMap,2,HomeBrew,2,HTML,2,HttpClient,2,Immutable,1,Installation,1,Interview Questions,6,Iterate,2,Jackson API,3,Java,32,Java 10,1,Java 11,6,Java 12,5,Java 13,2,Java 14,2,Java 8,128,Java 8 Difference,2,Java 8 Stream Conversions,4,java 8 Stream Examples,12,Java 9,1,Java Conversions,14,Java Design Patterns,1,Java Files,1,Java Program,3,Java Programs,114,Java Spark,1,java.lang,4,java.util. function,1,JavaScript,1,jQuery,1,Kotlin,11,Kotlin Conversions,6,Kotlin Programs,10,Lambda,2,lang,29,Leap Year,1,live updates,1,LocalDate,1,Logging,1,Mac OS,3,Math,1,Matrix,6,Maven,1,Method References,1,Mockito,1,MongoDB,3,New Features,1,Operations,1,Optional,6,Oracle,5,Oracle 18C,1,Partition,1,Patterns,1,Programs,1,Property,1,Python,2,Quarkus,1,Read,1,Real Time,1,Recursion,2,Remove,2,Rest API,1,Schedules,1,Serialization,1,Servlet,2,Sort,1,Sorting Techniques,8,Spring,2,Spring Boot,23,Spring Email,1,Spring MVC,1,Streams,31,String,61,String Programs,28,String Revese,1,StringBuilder,1,Swing,1,System,1,Tags,1,Threads,11,Tomcat,1,Tomcat 8,1,Troubleshoot,26,Unix,3,Updates,3,util,5,While Loop,1,

A quick guide to event handlers in java. How to add events and listeners to the buttons, text fields, and for different actions of the keyboard.

Источник