Thread - Join method

[solomon_13000]

When we run a java program, JVM will create the main thread in which the main function will be called. Inside the main thread we can have child thread. Now for the main thread to terminate the child thread must first be dead. To know if the child thread is alive or not we can do the following.

t1.join();
t1.isAlive() // returns a boolean value

Im assuming t1 as a thread object. Now how does the join() method play a role in finding out the status of the child thread. Also how does it tell the main thread that the child thread is all dead?. Besides that without the syntax t1.join(), the t1.isAlive() statement will result in an error. So what does the join() method do to the t1 thread object?.