Java Thread start()

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In this guide, you will learn about the Thread start() method in Java programming and how to use it with an example.

1. Thread start() Method Overview

Definition:

The Thread.start() method is used to start the execution of a new thread. The Java Virtual Machine calls the run() method of this thread.

Syntax:

public void start()

Parameters:

None.

Key Points:

- This method initiates a call to the run() method of the Thread class.

- Once the start() method is called, the Java runtime takes over and the JVM decides when the thread will actually run.

- Invoking the start() method on a thread that's already started will lead to an IllegalThreadStateException.

- It's essential to differentiate between start() and run(). Directly calling run() will execute the method in the current thread rather than starting a new thread.

2. Thread start() Method Example

public class ThreadStartExample {
    public static void main(String[] args) {
        // Create a new thread
        Thread newThread = new Thread(() -> {
            for(int i = 0; i < 5; i++) {
                System.out.println("Inside new thread");
            }
        });

        // Start the new thread
        newThread.start();

        for(int i = 0; i < 5; i++) {
            System.out.println("Inside main thread");
        }
    }
}

Output:

Inside main thread
Inside new thread
Inside main thread
Inside new thread
Inside main thread
Inside new thread
Inside main thread
Inside new thread
Inside new thread

Explanation:

In the example, we create a new thread and use the Thread.start() method to start its execution. The new thread prints "Inside new thread" 5 times, and the main thread prints "Inside main thread" 5 times. The exact order of the outputs might vary because the execution order of threads is not guaranteed. Therefore, different runs may produce slightly different interleaved outputs.