Volatile

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