Asynchronous and synchronous callbacks in Java

Sun Microsystems initially introduced Java, a programming language and computing platform, in 1995. It has grown from its modest origins to power a significant portion of the digital world of today by offering the solid foundation upon which numerous services and applications are developed. Java is still used in cutting-edge goods and digital services that are being developed for the future.

What is Asynchronous and Synchronous in Java?

Java's asynchronous programming paradigm enables teams to distribute workload and develop application features apart from the main application thread. The code is then synchronised with the main thread when the team is ready with the functionality.

Java's synchronisation feature allows for the management of many threads' access to any shared resource. Multiple threads attempt to access the same shared resources at once in the multithreading concept, leading to erratic outcomes. For reliable communication between threads, synchronisation is required.

What is Callback in Java?

The CallBack catchword defines functions in JAVA programming in organizations with many other programming languages. The CallBack characteristic is a controversy handed to another feature. The CallBack characteristic runs after a specific event is brought on on a selected agenda. The actual reason for the back of the CallBack feature is to tell a specific class about the operating repute of every other elegance. The CallBack function is beneficial when we work on some asynchronous tasks. The callback is likewise beneficial when the use of "event handlers" as it presents a few forms of notification when the consumer clicks a button on the front. So, we can take into account that the CallBack function performs an essential position while acting habitual programming tasks, which include B. Appearing diverse operations and downloading a few facts from the network. As for the application of the CallBack attribute in the JAVA programming language, it may be implemented through the use of an interface. Let's don't forget the Fashionable procedure for executing the CallBack function in JAVA programming.

The manner used within the implementation of the callback feature?

  • We start by defining the strategies of the interface that we need to invoke after the callback.

  • To put into effect interface callback strategies, outline a category.

  • To register a callback interface, set a reference to a random magnificence.

  • Use the described reference to name the CallBack method.

Types of callbacks in Java?

  • Synchronous call

  • Asynchronous call

Synchronous call Syntax

  • Step 1 − Make a interface.

  • Step 2 − Make void expression.

  • Step 3 − Make class directory

  • Step 4 − Make public void.


// This is a program in Java for understanding
// the implementation of "Asynchronous call".

interface ExampleEventListener {
   // Any type of method
   // can be defined below
   void exampleEvent();

// Define a random class
// in which the main section is also
// defined
public class Example2 {
   private ExampleEventListener mListener; // This is the listener field

   // Set up the Listener below using the public
   // access modifier and the void return type
   public void registerExampleEventListener(ExampleEventListener mListener) {
      this.mListener = mListener;

   // This is my synchronous task
   // which needs to be performed.
   public void myStuff() {

      // An async task always executes within a new thread
      // so a new thread must be created in order to execute.

      System.out.print("The task being performed ");
      System.out.println("here is a synchronous task");

      // Check whether the listener is registered or not.
      if (this.mListener != null) {
         // Invoke the callback method of the ExampleEventListener class

   public static void main(String[] args) {
      Example2 obj = new Example2();
      ExampleEventListener mListener = new Myclass();

class Myclass implements ExampleEventListener {
   public void exampleEvent() {
      System.out.print("Performing callback after ");
      System.out.print("the completion of the synchronous task");
      // Perform any random routine operation
   // Some Myclass methods


The task being performed here is a synchronous task
Performing callback after the completion of the synchronous task

We came to know from the significant output, it is understandable the role of a synchronous call using the CallBack method in the JAVA programming language. We can observe that each step discussed is tied into the above program. In the above mentioned, we used the event listener interface in the program.

When is a Synchronous call used?

We use a synchronous call in situations where several tasks in the program need to be executed one after the other in a certain order. Less time-consuming tasks are also considered to be invoked synchronously.

Asynchronous call Syntax

  • Step 1 − Create a interface.

  • Step 2 − Make a void class.

  • Step 3 − Make public void class.

  • Step 4 − Make public void.


interface ExampleCallEventListener {
   void exampleCallEvent();

public class Example1 {

   private ExampleCallEventListener mListener;

   public void registerExampleCallEventListener(ExampleCallEventListener mListener) {
      this.mListener = mListener;

   public void myStuff() {
      new Thread(new Runnable() {
         public void run() {
            System.out.println("This is an example and tutorial here");

            if (mListener != null) {

   public static void main(String[] args) {
      Example1 obj = new Example1();
      ExampleCallEventListener mListener = new MyClass();

class MyClass implements ExampleCallEventListener {
   public void exampleCallEvent() {
      System.out.println("Performing callback after the completion of an Async Task");


This is an example and tutorial here
Performing callback after the completion of an Async Task

After we came to know from the above mentioned program, we can accept the role of an asynchronous call using the CallBack method in the JAVA programming language. We can observe that a new thread is created and the callback is invoked within that thread. We used the event listener interface in the program.

When is an Asynchronous Call used?

We use asynchronous invocation in situations where program tasks are not dependent on each other, so an interruption in one task does not affect the others. Tasks that take longer are also considered to be called Asynchronous.

Difference between Synchronous and Asynchronous call is Java


A Synchronous call is a callback where the executing code waits for an event before continuing. Asynchronous calls, on the other hand, refer to callbacks that do not block transactions. This is the prime difference between synchronous and asynchronous calls in Java.


Java has both synchronous and asynchronous calls, which differ in their handling of code execution while waiting for an event. Unlike in synchronous calls or callbacks. Asynchronous ones allow the program to continue executing code during this wait period.


Programmers have access to two different callback methods depending on their needs for task completion- synchronized or asynchronous based on what suits them best. Synchronized callbacks come in handy when performing routine tasks requiring minimal processing time whereas asynchronous ones suit more complex and disconnected processes with lengthy execution times instead. Analogously, synchronous versus asynchronous calls differ from one another in Java-based coding practices too without exceptions being made.


Implementing Java programming allows for both synchronous and asynchronous call utilization. Unlike with asynchronous call execution, where programs may execute additional pieces of code uninterrupted, synchronous calling requires events to occur before any further actions can be taken by the system or program at hand.

Updated on: 01-Aug-2023

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