start() starts the thread method
When run() calls the start() method, what is actually executed is the method body of the method.
sleep() puts the current thread to sleep, automatically wakes up when the sleep expires, and enters the runnable state instead of the running state.
yield() pauses the currently executing thread object. The JVM thread scheduler calls other high-priority threads based on the priority preemption mechanism. The priority value range is 1 (Thread.MIN_PRIORITY) -- 10 (Thread.MAX_PRIORITY), The default number of threads created is 5 (NORM_PRIORITY)
setPriority(int newPriority) sets the new priority of the thread
join() waits for the thread to terminate before starting to execute the current thread; for example, thread A calls the join() method of thread B and waits for thread B to terminate before continuing to execute thread A. Thread B terminates and thread A enters a runnable state.