Java notify() Method in Threads Synchronization with Examples

17 Jun, 2021
The notify() method is defined in the Object class, which is Java’s top-level class. It’s used to wake up only one thread that’s waiting for an object, and that thread then begins execution. The thread class notify() method is used to wake up a single thread. If multiple threads are waiting for notification, and we use the notify() method, only one thread will receive the notification, and the others will have to wait for more. This method does not return any value.
It is used with the wait() method, in order to communicate between the threads as a thread that goes into waiting for state by wait() method, will be there until any other thread calls either notify() or notifyAll() method.
Syntax:
public final void notify() ; 
Implementation:
The synchronized keyword is used for exclusive accessing.
wait() instructs the calling thread to shut down the monitor and sleep until another thread enters the monitor and calls notify().
notify() wakes up the first thread that called wait() on the same object.
Example
Java
// Java program to Illustrate notify() method in Thread// Synchronization.  // Importing required classesimport java.io.*;import java.util.*;  // Class 1// Thread1// Helper class extending Thread classpublic class GFG {      // Main driver method    public static void main(String[] args)    {          // Creating object(thread) of class 2        Thread2 objB = new Thread2();          // Starting the thread        objB.start();          synchronized (objB)        {              // Try block to check for exceptions            try {                  // Display message only                System.out.println(                    "Waiting for Thread 2 to complete...");                  // wait() method for thread to be in waiting                // state                objB.wait();            }              // Catch block to handle the exceptions            catch (InterruptedException e) {                  // Print the exception along with line                // number using printStackTrace() method                e.printStackTrace();            }              // Print and display the total threads on the            // console            System.out.println("Total is: " + objB.total);        }    }}// Class 2// Thread2// Helper class extending Thread classclass Thread2 extends Thread {      int total;      // run() method  which is called automatically when    // start() is initiated for the same    // @Override    public void run()    {          synchronized (this)        {              // iterating over using the for loo            for (int i = 0; i < 10; i++) {                  total += i;            }              // Waking up the thread in waiting state            // using notify() method            notify();        }    }}
Waiting for Thread 2 to complete...
Total is: 45
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