Java's synchronized method is a fundamental part of Java's concurrency mechanism. It provides a way to control access to method scopes and code blocks to ensure that only one thread can execute a particular piece of code at any given time. This is crucial in multi-threaded applications to prevent thread interference and memory consistency errors. This article dives deep into the concept, usage, and examples of synchronized methods in Java.

What is a Synchronized Method?

A synchronized method in Java is a method that is marked with the keyword synchronized in its declaration. Using this keyword ensures that once a thread has begun executing the synchronized method, no other thread can execute any synchronized method on the same object until the first thread finishes execution.

Syntax

• When a thread enters a synchronized instance method, a lock is acquired on the current object (this ).
• When a thread executes a static synchronized method, the lock is acquired on the class object associated with the class.
• Synchronization can significantly affect performance because it can impose a locking mechanism that is expensive in terms of resources.
• Proper understanding of locking and multi-threading is essential to avoid problems like deadlocks.
• For performance reasons, synchronize only critical sections of code rather than entire methods.
• Deadlocks: Situations where two or more threads are waiting for each other to release locks can lead to a standstill.
• Contention: Threads competing for the same lock can lead to performance degradation.
• Thread Safety: While synchronized can help make a class thread-safe, improper usage or other unsafe operations might still lead to unsafe states.
• Volatile keyword: Used when threads may read a variable but not modify it, achieving visibility without locking.
• Explicit Locks: Java's java.util.concurrent.locks package provides more flexible and complex locking mechanisms compared to the monitor lock provided by synchronized .
• Atomic Variables: For certain situations, java.util.concurrent.atomic provides classes like AtomicInteger that offer lock-free thread-safe operations.