Thread join usage (Thread execution sorting)

This is a reprinted explanation:

The thread must be started before it can join. Only when it is started can it operate on the thread.

If A thread is called A, see the following sample code.
A. start (); // start thread
A. join (); // invites thread A to execute the statement first. This thread suspends the execution first. After thread A finishes executing the Statement, the main thread continues to execute the statement.

System. out. println ("OK"); // this statement will be executed only after the main thread obtains the execution right after thread A finishes executing the statement.

Example:

In the code segment, I commented out all join operations. The output result is:

I open the join comments for all comments. The output result is as follows:

Conclusion: We can use join to sort the thread order to achieve the effect of sequential thread execution.