Can we start the thread twice?

No, you cannot start a thread twice in Java. Once a thread has been started and has completed its execution (either by finishing its run() method or by encountering an unhandled exception), it cannot be started again.

Here’s why this is the case:

1. Thread State: In Java, a thread has a lifecycle that includes various states (NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED). Once a thread transitions to the TERMINATED state, it cannot be brought back to a RUNNABLE state by calling start() again.
2. IllegalThreadStateException: If you try to call start() on a thread that has already been started (and has not finished or been terminated), it will throw an IllegalThreadStateException. This exception indicates that the thread is not in an appropriate state to be started again.

Example of IllegalThreadStateException:

Thread thread = new Thread(() -> {
    System.out.println("Thread is running...");
});

thread.start(); // First start

// Trying to start the thread again
thread.start(); // This will throw IllegalThreadStateException

Workaround:

If you want to execute the same task multiple times using threads, you should create a new instance of Thread or Runnable each time you need to start a new execution. For example:

Runnable task = () -> {
    System.out.println("Thread is running...");
};

Thread thread1 = new Thread(task);
thread1.start(); // First execution

Thread thread2 = new Thread(task); // New instance of Thread with the same task
thread2.start(); // Second execution

In this way, you can achieve multiple executions of a task using threads by creating new thread instances for each execution.

Conclusion:

Once a thread has completed its execution or has been terminated, attempting to start it again using start() will result in an IllegalThreadStateException. To execute a task multiple times using threads, create new instances of Thread or Runnable for each execution. This ensures proper thread lifecycle management and avoids exceptions related to thread state violations in Java.