Achieving Thread Safety in Java with Synchronized Blocks or Methods

Java provides several mechanisms to maintain thread safety in your code. The correct way mentioned in the quiz is by using synchronized blocks or methods.

Synchronization is a capability that prevents concurrent access to shared resources by different threads in a multithreaded environment. This is achieved by making use of a concept called monitor lock, which is an entity that is owned by a thread for mutual exclusion.

A synchronized method in Java is marked with the synchronized keyword. If a thread invokes a synchronized method, it automatically acquires the intrinsic lock for that method's object and releases it when the method returns.

Here's a simple synchronized method in Java:

public synchronized void syncMethod(){
  // Critical section code here
}

If another thread tries to invoke a synchronized method while the initial thread is executing, it will be blocked until the initial thread finishes and releases the lock.

You can also synchronize blocks of code rather than an entire method. A synchronized block in Java is synchronized on some object. All synchronized blocks synchronized on the same object can only have one thread executing inside them at a time:

public void syncBlock(){
  synchronized(this){
      // Synchronized block code here
  }
}

Here, this refers to the current object, meaning the synchronized block is synchronized on the current object.

However, remember that synchronization should only be applied when absolutely necessary as it can affect performance. Overuse of synchronization might lead to thread contention, where many threads are trying to access the same resources, eventually starving or deadlocking some threads.

While using the 'volatile' keyword and making methods or variables private can play some role in achieving thread safety, they alone are not sufficient or proper ways to ensure thread safety.

In addition, 'volatile' does not ensure atomicity. The volatile keyword in Java is used to mark a Java variable as "being stored in main memory". More precisely, that means, that every read of a volatile variable will be read from the main memory, and not from the CPU cache, and that every write to a volatile variable will be written to main memory, and not just to the CPU cache.

And making methods and variables private only affects visibility and encapsulation, but does not inherently make the code thread-safe. Multiple threads can still access private methods and variables of a shared object, potentially leading to inconsistent state changes.

Therefore, to achieve thread safety in java, it's recommended to make use of synchronized blocks or methods, depending upon the specific requirement of your application.