Understanding Synchronization in Java: Concepts, Importance, and Implementation

In a multi-threaded application, two or more threads may try to access shared resources simultaneously. This can lead to unpredictable behavior, data inconsistency, or even application crashes. To handle such scenarios effectively, Java provides a mechanism called Synchronization.

If you're aiming to become a professional Java developer, learning synchronization is a must. Top-rated Java classes in Pune and hands-on sessions at a certified java training institute in Pune often include synchronization as a core part of advanced Java programming and real-world project development.

Let’s dive into what synchronization is, why it matters, how it works, and the types of synchronization available in Java.

🧵 What Is Synchronization in Java?

Synchronization in Java is a process that controls access to shared resources by multiple threads. It ensures that only one thread can access a resource (like a method or block of code) at a time, preventing data inconsistency and race conditions.

Java achieves synchronization using the synchronized keyword. This keyword is used to lock an object or method so that no other thread can access the same resource until the lock is released.

🧠 Why Do We Need Synchronization?

Let’s say you have two threads updating the balance of a bank account. If both threads try to update it at the same time, one thread's changes might overwrite the other’s. This situation is known as a race condition.

Common Issues Without Synchronization:

• Data inconsistency

• Unpredictable outputs

• Race conditions

• Deadlocks (if not handled properly)

To avoid these issues, synchronization provides a lock mechanism that ensures atomic access to shared resources.

🔧 How to Implement Synchronization in Java

There are mainly two ways to apply synchronization in Java:

1. Synchronized Method

When you declare a method as synchronized, only one thread can execute it on the same object at any given time.

Example:

If two threads try to access this method, one will wait until the other completes execution.

2. Synchronized Block

This allows you to synchronize only a portion of your code, which improves performance and control.

Example:

Synchronized blocks are more efficient than synchronized methods when you don’t need to lock the entire method.

🔒 Locking and Object Monitor

Every object in Java has a built-in monitor lock. When a thread enters a synchronized method or block, it acquires the object’s lock. Other threads attempting to enter the synchronized block must wait until the lock is released.

This lock is released when:

• The synchronized method/block completes execution

• An exception is thrown and caught outside the method

⏳ Thread Interference Example

Here's what could go wrong without synchronization:

If multiple threads access increment() simultaneously, the result may be inconsistent. Synchronizing the method solves this:

You’ll get to build such multi-threaded scenarios in advanced modules at top Java classes in Pune.

🛠️ Types of Synchronization in Java

Java offers several types of synchronization mechanisms:

1. Process-Level Synchronization

This involves synchronizing code within a single process using:

• Synchronized Methods

• Synchronized Blocks

2. Thread-Level Synchronization

Useful when different threads access shared resources. Techniques include:

• Using synchronized keyword

• Using ReentrantLock (from java.util.concurrent.locks)

• Using Atomic classes (like AtomicInteger)

⚙️ Static Synchronization

If you want to synchronize a static method, the lock is applied on the class object, not the instance.

Example:

Multiple threads calling this method will lock the entire class object.

🔄 ReentrantLock: An Advanced Option

Java 5 introduced ReentrantLock for more advanced locking control.

Benefits:

• Try-locking (check if lock is available)

• Fairness policies

• Timeout-based locking

Example:

🧠 Best Practices for Using Synchronization

⚠️ Common Synchronization Problems

1. Deadlock

Occurs when two threads wait for each other’s locks and neither proceeds.

2. Starvation

A thread keeps waiting indefinitely because other high-priority threads keep executing.

3. Livelock

Threads keep changing state in response to each other but never make progress.

✅ Solution:

• Use proper locking hierarchy

• Keep synchronized blocks small

• Avoid nested synchronization

💻 Real-World Example: Banking Transaction System

Without synchronization:
Two users withdraw money at the same time—resulting in a negative balance.

With synchronization:
Only one thread can complete the withdrawal at a time—ensuring data integrity.

Projects like these are taught in-depth during advanced modules in Java classes in Pune, with a focus on performance and safety.

🎓 Why Learn Synchronization from a Java Training Institute?

While online tutorials help with theory, real-world implementation is key. Certified java training institutes in Pune offer:

• Instructor-led practical sessions

• Projects with real-time multithreading and synchronization use cases

• Mock interviews with multithreading questions

• Resume prep focused on backend development skills

🧪 Mini Project Idea: ATM Simulation with Synchronization

Features:

• Withdraw and deposit methods

• Balance update with synchronized methods

• Multiple user threads accessing the same account