Understanding the 'synchronized' Keyword in Java Multi-threading

In Java, the 'synchronized' keyword is a crucial feature when working within multi-threaded environments. The main purpose of the 'synchronized' keyword is to ensure that only a single thread can access a particular method or block at a given time.

This is essential in preventing issues related to thread interference and memory consistency errors, enhancing the predictability and reliability of your code in multi-threaded environments.

The Functionality of 'synchronized' Keyword

When a method or block is synchronized, it acquires a lock on a monitor, normally done using the 'this' keyword (when referring to the current object) or the class object. When a thread wants to access this synchronized code, it must first acquire this lock.

While one thread holds this lock, all other threads attempting to access the same block or method are blocked, ensuring exclusive access. Once the thread holding the lock finishes execution of the method or block, it releases the lock, allowing another thread to acquire it and access the method or block.

Here is a simple example of a synchronized method:

class Counter {
    private int count = 0;

    // Synchronized method 
    public synchronized void increment() {
        count++;
    }
}

In the above example, if two threads simultaneously call the increment() method on the same Counter object, they will not interfere with each other.

Best Practices and Additional Insights

While the 'synchronized' keyword ensures safe and predictable behavior of threads, it also introduces the potential for thread contention, which can lead to performance issues or tread deadlock. Therefore, it's generally best practice to limit the scope of synchronization to the smallest possible section of code.

Furthermore, it is worth noting that synchronization is not universally applicable. Some tasks are inherently non-thread-safe and cannot be made thread-safe using the 'synchronized' keyword.

In summary, the 'synchronized' keyword is a fundamental tool in Java for managing concurrency in multi-threaded environments. It guarantees that only one thread can access a synchronized method or block at a time, preventing thread interference and memory inconsistency errors. However, indiscriminate use can lead to thread contention and decreased performance, so it should be applied judiciously.