Java Multithreading, Concurrency, and Parallelism — Part 4

Multiple Threads and their Stacks

In part-3 we have seen how threads can be created and we also explored the life cycle of a thread to some extent. In this article, we will look at how threads maintain their local variables and call stacks.

Each thread in Java has a private stack associated with it. When a thread is created in Java Virtual Machine, a JVM stack local to that thread is also created.

Below is a simple java application that has one user-defined thread named MyThread along with the main thread.

As you can see in the above program there are two threads: main and MyThread.

Three things are happening in main thread.

1. The main() is invoked from themain thread. main() and main are different. main() — A regular java method. main: without parenthesis, a java thread).
2. main() in turn calls methodOne()
3. main() creates and stars a user-defined thread named MyThread.

Now MyThread simply calls methodTwo.

Here is how the stacks look like for each of these two threads.