Why specifically JOIN? What does it mean, what will happen? Are there other options for JOIN operation?

In the context of Java and multithreading, the join() method is used to make one thread wait for the completion of another. When you call thread.join(), the current thread is blocked and waits until the thread finishes.

This is important for synchronizing thread execution, for example, to ensure that data processed by another thread is ready for use.

Variants of join:

• join() — waits indefinitely until the thread finishes.
• join(long millis) — waits for the specified number of milliseconds, then continues execution even if the thread has not finished.
• join(long millis, int nanos) — waits with nanosecond precision.

Example:

Thread t = new Thread(() -> {
    // some work
});
t.start();

try {
    t.join(); // wait for thread t to finish
} catch (InterruptedException e) {
    e.printStackTrace();
}
// here, thread t has already finished

Thus, join is a way to organize the sequence of thread execution.