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Synchronization & Thread Interaction

Synchronization and thread interaction are crucial aspects of multi-threaded programming in Java. These concepts are used to coordinate the activities of multiple threads and ensure that they access shared resources in a safe and controlled manner

Synchronization in Java

Synchronization in Java is primarily achieved using the synchronized keyword, which can be applied to methods or blocks of code to control access to shared resources.
					public synchronized void synchronizedMethod() {
    // Synchronized method code


Note: When a method is declared as synchronized, only one thread can execute it at a time for the same object instance.

Synchronized Blocks

Synchronized blocks allow you to specify a block of code that should be executed by only one thread at a time. The lockObject serves as a monitor or mutex, ensuring exclusive access to the critical section.

					synchronized (lockObject) {
    // Critical section of code


Intrinsic Locks (Monitors)

In Java, each object has an intrinsic lock, also known as a monitor. When you use the synchronized keyword, you are acquiring and releasing this lock, preventing multiple threads from simultaneously executing synchronized blocks or methods on the same object.
					synchronized (lockObject) {
    // Critical section of code


Thread Interaction in Java

Thread interaction involves coordination and communication between threads. Java provides several mechanisms for thread interaction:

'wait()', ‘notify()', and ‘notifyAll()':

These methods are used in conjunction with synchronized blocks to allow threads to wait for a condition and be notified when the condition changes.

					synchronized (lockObject) {
    while (conditionIsNotMet) {
        // Release the lock and wait
    // Perform actions when the condition is met

// In another thread:
synchronized (lockObject) {
    // Change the condition
    // Notify a waiting thread


`BlockingQueue`: The BlockingQueue interface and its implementations (e.g., LinkedBlockingQueue,

`ArrayBlockingQueue`: provide a thread-safe way to exchange data between threads. Threads can block until the queue is not empty or not full.

`CountDownLatch: The CountDownLatch class allows one or more threads to wait until a specified count of operations completes. It’s useful for tasks that depend on multiple subtasks.

`Semaphore: Semaphores are used to control access to a shared resource by limiting the number of threads that can access it simultaneously.

  • Condition Variables: Java also provides Condition objects through the java.util.concurrent.locks package. These can be used for more fine-grained thread synchronization.


  • Thread Interruption: You can use thread interruption to signal a thread to stop its execution. A thread can check its interrupted status using the Thread.isInterrupted() method.
Effective synchronization and thread interaction are essential for writing safe and reliable multi-threaded Java programs. Properly designed synchronization and coordination mechanisms help prevent data corruption, deadlocks, and race conditions, ensuring the correct and efficient execution of concurrent tasks.