What is the synchronised method in Java?

What is the synchronised method in Java?

I'd be happy to explain the synchronized method in Java!

In Java, a synchronized method is a way to ensure that multiple threads do not access a shared resource at the same time. This is achieved through the use of a lock mechanism, which allows only one thread to execute the method at a time.

When a thread requests to enter a synchronized method, it must acquire a lock on an object (the "synchronization object") before proceeding. If another thread already holds the lock, the requesting thread will be blocked until the lock is released.

Here's a high-level overview of how synchronization works in Java:

To illustrate this concept, let's consider an example:

public class BankAccount {
private int balance = 0;
public synchronized void withdraw(int amount) {
if (balance >= amount) {
balance -= amount;
}
}
}

In this example, we have a BankAccount class with a withdraw method that updates the account balance. To ensure that only one thread can update the balance at a time, we mark the method as synchronized.

When multiple threads try to withdraw money from the same account simultaneously, only one thread will be allowed to execute the withdraw method at a time. The other threads will be blocked until the lock is released.

Synchronization in Java is implemented using the Object class's notify, notifyAll, and wait methods, which allow threads to coordinate their behavior and wait for specific events to occur.

In addition to using synchronization objects like Object, Java also provides several other ways to achieve thread safety, including:

Overall, synchronized methods are an essential tool for achieving thread safety in Java, and understanding how they work is crucial for developing robust and efficient multithreaded applications.

How do you call a method synchronously in Java?

I'd be happy to help with that!

In Java, calling a method synchronously means that the method is executed and completed before the main program continues executing. This is achieved by using various synchronization mechanisms provided by Java.

One common way to call a method synchronously in Java is to use the join() method available in the Thread class. The join() method causes the current thread to wait until the specified thread terminates, but it does not release any locks that might be held by the thread. If you want to release any locks before waiting for the thread to finish, use the join(long timeout) or join(long timeout, int nanos) methods.

Here's an example of using the join() method:

Thread thread = new Thread(new Runnable() {
public void run() {
System.out.println("This is a test");
}
});
thread.start();
try {
thread.join();  // Wait until the thread finishes execution
} catch (InterruptedException e) {
e.printStackTrace();
}

Another way to call a method synchronously in Java is to use synchronized keyword. The synchronized keyword ensures that only one thread can execute the code at any given time, thus preventing concurrent access to shared resources.

Here's an example of using the synchronized keyword:

public class SynchronizedExample {
public static synchronized void printMessage() {
System.out.println("This is a test");
}
}

You can also use CountDownLatch or Semaphore from java.util.concurrent package to achieve synchronization.

Here's an example of using CountDownLatch:

public class CountDownLatchExample {
public static void main(String[] args) throws InterruptedException {
final CountDownLatch latch = new CountDownLatch(1); // Create a latch with 1 count
Thread thread = new Thread(new Runnable() {
public void run() {
System.out.println("This is a test");
latch.countDown(); // Decrement the count
}
});
thread.start();
latch.await();  // Wait until the count reaches zero
}
}

And here's an example of using Semaphore:

public class SemaphoreExample {
public static void main(String[] args) throws InterruptedException {
final Semaphore semaphore = new Semaphore(1);  // Create a semaphore with one permit
Thread thread = new Thread(new Runnable() {
public void run() {
System.out.println("This is a test");
semaphore.release();  // Release the permit
}
});
thread.start();
semaphore.acquire();  // Acquire the permit (wait until released)
}
}

In summary, Java provides various mechanisms to call methods synchronously, including join(), synchronized keyword, CountDownLatch, and Semaphore. Each mechanism has its own strengths and weaknesses, depending on your specific use case.