Volatile

A variable declared with the volatile keyword guarantees that any thread reading the field will see the most recently written value.

Volatile variable value will be directly written to and read from the main memory instead of CPU cache.

In Java, the volatile keyword is used to indicate that a variable's value will be modified by different threads. Declaring a variable as volatile ensures that any read or write operation on that variable will be directly performed on the main memory, rather than using a local copy (cache). This guarantees visibility of changes across threads.

https://raw.githubusercontent.com/vsaravanan/java22/master/src/main/java/com/saravanjs/java22/console/multithreading/Volatile.java

public class VolatileTest {
private boolean flag = false;

public void writer() {
flag = true;
    }

public void reader() {
if (flag) {
System.out.println("Flag is true");
        }
else {
System.out.println("Flag is false");
        }
    }

public static void main(String[] args) throws InterruptedException {
VolatileTest sharedData = new VolatileTest();

Thread writerThread = new Thread(() -> {
try {
Thread.sleep(1);
            } catch (InterruptedException e) {
throw new RuntimeException(e);
            }
sharedData.writer();
        });

Thread readerThread = new Thread(() -> {
sharedData.reader();
        });
writerThread.start();
readerThread.start();

    }
}

Flag is false

public class VolatileTest {
 private volatile boolean flag = false;


 public void writer() {
 flag = true;

    }


 public void reader() {
 if (flag) {
 System.out.println("Flag is true");

        }
 else {
 System.out.println("Flag is false");

        }

    }


 public static void main(String[] args) throws InterruptedException {
 VolatileTest sharedData = new VolatileTest();


 Thread writerThread = new Thread(() -> {
 sharedData.writer();

        });


 Thread readerThread = new Thread(() -> {
 sharedData.reader();

        });
 writerThread.start();
 readerThread.start();



    }

}

Flag is true