Can Synchronized Methods in the Same Class Run Concurrently on the Same Object?

If I synchronize two methods on the same class, can they run simultaneously on the same object?

class A {
    public synchronized void methodA() {
        // method A logic
    }

    public synchronized void methodB() {
        // method B logic
    }
}

In Java, synchronized methods ensure that only one thread can execute a method at a time on a specific object instance. Therefore, if two methods are synchronized within the same class and are invoked on the same object, they cannot run concurrently.

class A {
    private final Object lockA = new Object();
    private final Object lockB = new Object();

    public void methodA() {
        synchronized(lockA) {
            // method A logic
        }
    }

    public void methodB() {
        synchronized(lockB) {
            // method B logic
        }
    }
}

Causes

• Both methods are synchronized, meaning they acquire the intrinsic lock of the instance on which they're invoked before executing.
• Java's synchronized keyword ensures thread safety, preventing multiple threads from executing synchronized code simultaneously for the same object.

Solutions

• To allow concurrent execution, consider using the synchronized block on a separate object, thereby not locking the entire object instance.
• Refactor the methods to use different synchronizers, such as using explicit locks from the `java.util.concurrent.locks` package.

Mistake: Assuming that synchronizing different methods within the same object allows them to run concurrently.

Solution: Understand that synchronized methods lock the same object instance. Use separate locks if you need concurrency.

Mistake: Not using the synchronized keyword properly in a multi-threaded context.

Solution: Ensure synchronized blocks are used correctly to avoid threading issues.