How to Use Locks in Java

When endeavoring to compose intricate multi-threaded code, it becomes paramount to bestow careful attention upon the concurrent access of shared mutable variables by multiple threads. Fortunately, Java has long embraced the field of thread synchronization, a boon since its nascent stages, through the utilization of the synchronized keyword. Synchronization, in the context of multi-threading, entails the establishment of a consistent interplay.

While in synchronization, a code block encapsulated within the confines of synchronization can solely be executed by a single thread at any given moment. To navigate this landscape, Java furnishes a set of essential methods. These include lock(), which facilitates the acquisition of the lock, unlock(), which graciously relinquishes the lock, tryLock(), allowing for the waiting upon a lock for a specified duration of time, and newCondition(), which serves to engender a Condition object, among other noteworthy techniques.

By using these synchronization mechanisms, developers can foster a robust and orchestrated environment for concurrent code execution. The synchronization of shared mutable variables bolsters data integrity, assuring that threads navigate the intricacies of parallel execution without compromising the consistency of the underlying data. Through the judicious application of synchronization, the risk of race conditions and data corruption is mitigated, ensuring harmonious and predictable outcomes within the multi-threaded paradigm.

What is an object's lock in Java and which object's have locks?

Object Level Locking serves as a fundamental mechanism employed to synchronize non-static sections of code, effectively granting exclusive access to a singular object at any given time. By utilizing this locking mechanism, developers can ensure that only a single object possesses the monitor and gains the privilege to access the non-static elements within the code. Object Level Locking becomes particularly pertinent in scenarios where multiple threads are concurrently accessing and sharing an instance of a class that either implements the Runnable interface or extends the Thread class.

It is important to note that both objects and classes possess inherent locks. These locks serve as guardians, protecting critical sections of code from simultaneous access by multiple threads, thus preventing race conditions and data integrity issues. In the context of Object Level Locking, each instance of an object holds its own lock, ensuring that only one thread at a time can acquire the lock and gain access to the associated non-static content.

Developers can strategically employ Object Level Locking to synchronize specific sections of code where the shared object's state must be accessed and modified in a controlled manner. By restricting access to these critical sections, conflicts arising from concurrent execution of code are mitigated, leading to predictable and consistent outcomes.

Difference between class locking and object locking in Java

Class Level Locking assumes a crucial role in ensuring thread safety for static content within a class. It serves as a mechanism to synchronize and protect class-level data, enabling concurrent access by multiple threads without compromising data integrity. The distinguishing factor between Class Level Locking and Object Level Locking lies in the locking target: while a static synchronized method locks on the class instance, a non-static synchronized method locks on the object itself.

When it comes to static content within a class, such as static variables or static methods, Class Level Locking becomes essential to prevent data races and maintain consistency in a multi-threaded environment. By applying the synchronized keyword to static methods or code blocks, developers can ensure that only one thread at a time can access and modify the shared class-level data.

In the case of a static synchronized method, the lock is acquired on the class instance itself. This means that other threads attempting to access the same static synchronized method must wait until the lock is released, guaranteeing exclusive access to the shared static content. This synchronization mechanism ensures that modifications to static variables or invocations of static methods occur in an orderly and synchronized manner.

On the other hand, non-static synchronized methods, typically associated with instance methods within a class, acquire the lock on the specific object instance being accessed. This allows for synchronized access to non-static content, preserving data integrity within the object's state. Different object instances can execute non-static synchronized methods concurrently, as each instance holds its own lock, independent of other instances.


Locks in Java can be used to manage concurrent access to shared resources, providing synchronized and exclusive access to critical sections of code, ensuring thread safety and preventing data corruption or race conditions.