Understanding Synchronized Methods in Java: Will 'Hello World' Be Printed?

Summary: Explore the behavior of synchronized methods in Java and find out whether "Hello World" will be printed when a thread waits in foo() and another calls it.
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Java concurrency can be intricate, yet it's crucial for developing robust and efficient multi-threaded applications. A key feature in Java's concurrency model is the synchronized method. Often, developers encounter scenarios where they need to determine whether actions, such as printing "Hello World," will occur when multiple threads interact with synchronized code. Let's explore what happens in such a situation using a hypothetical example involving the foo() method.

The Scenario

Consider a Java class that has a synchronized method named foo(). The method is responsible for printing "Hello World". Here's a simplified version of what this might look like:

[[See Video to Reveal this Text or Code Snippet]]

In this context, when one thread (let's call it threadA) calls the foo() method and another thread (threadB) attempts to do the same, we need to understand how Java handles this concurrency situation due to the synchronized keyword.

How synchronized Works

Java's synchronized keyword ensures that a method or a block of code can only be accessed by one thread at any given time. This helps in preventing race conditions and ensures thread safety.

When a thread calls a synchronized method, it acquires the object's intrinsic lock or monitor.

While holding the lock, no other thread can enter any synchronized method in the same object.

Once the thread exits the method or the execution finishes, the lock is released.

Will "Hello World" Be Printed by threadB?

Given the above information, here's what happens step by step:

ThreadA calls foo(): It acquires the lock on the FooPrinter object and prints "Hello World".

ThreadB waits: If threadA has not finished executing the foo() method, threadB will be blocked from entering the method until threadA releases the lock.

ThreadA finishes: After threadA exits foo() and releases the lock, threadB can then acquire the lock and proceed to enter the method.

Therefore, "Hello World" will indeed be printed by threadB, but only after threadA has finished its execution and exited the foo() method. This sequential access due to synchronization ensures that the state within the object remains consistent.

Implications for Developers

Understanding this behavior is critical when designing concurrent applications. Knowing that a thread will wait until another releases a synchronized lock helps in planning the flow of execution and preventing scenarios where resources might get blocked indefinitely. It is a fundamental aspect of achieving concurrency control in Java with synchronized methods.

Remember, while synchronized methods simplify protection against race conditions, developers must still account for performance trade-offs due to blocked threads potentially resulting in decreased throughput.

By mastering synchronized methods and the nuances of Java's concurrency mechanisms, developers can create more reliable and efficient multi-threaded applications.