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Explore the crucial differences between `start()` and `run()` methods in Java threading, and enhance your multithreading skills with a clear, insightful guide.
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Understanding the Difference Between start() and run() in Java Threads

Java multithreading can be a tricky concept to grasp for beginners. A common misconception revolves around the usage of the start() and run() methods when working with threads. In this guide, we'll explore the important distinctions between these two methods and clarify their functionalities to enhance your understanding of Java threading.

What You Need to Know About Threads

In Java, a thread is a lightweight process and is defined in the Thread class. The execution of a thread can be controlled using methods such as start() and run(). However, how you use these methods results in significantly different behaviors.

Understanding run() and start()

start() Method:

When you call start(), a new thread is created, and the run() method is executed by that thread. This means that the newly created thread runs concurrently with the main thread, allowing both threads to operate independently. This is where the magic of multitasking takes place.

run() Method:

If you invoke the run() method directly (e.g., t1.run()), it is simply a method call on the current thread. This means that the run() method will execute sequentially, not launching a new thread. As a result, the main thread handles the entire execution of the run() method, and the program does not leverage the benefits of threading.

Practical Example

To illustrate these concepts, let’s dive into a code example.

Code Snippet

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Output with start():

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Change to run():

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Output with run():

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Breaking Down the Outputs

Using start(): The output shows alternate executions of firstThread and secondThread. This demonstrates how both run concurrently, with the computer switching back and forth between the threads during their execution.

Using run(): In contrast, this output shows firstThread completing all its iterations before secondThread starts. Here, the main thread executes tasks in a sequential manner without the clipping of tasks that comes with the multithreading advantage.

Important Takeaways

Concurrency: The start() method allows two threads to execute simultaneously, while calling run() means that the run() method is performed on the current thread in normal, sequential order.

Thread Creation: The new operator creates an instance of the thread, but it is the start() method that makes it a separate concurrent thread. Calling run() does not create a new thread; it simply executes the method on the calling thread.

Understanding Thread Context: When using this.getName(), it refers to the name of the thread object. Instead, using Thread.currentThread().getName() gives context about the currently executing thread, which is particularly important to maintaining accurate thread behavior.

Conclusion

Understanding the difference between start() and run() is crucial for efficient multithreading in Java. By using start(), you harness the full potential of concurrent execution, while directly invoking run() leads to sequential processing, negating the benefits of multithreading.

As you continue working with Java threads, keep in mind the significance of these two methods, and apply your understanding practically to enhance your programming skills.