Java Multithreading - Timeline

• JDK 1 - In the first Java release classes like java.lang.Thread, java.lang.ThreadGroup were introduced
• JDK 2 to JDK 4- No major changes were introduced
• JDK 5 - included multiple concurrency utilities. Executor, semaphore, mutex, barrier, latches, concurrent collections and blocking queues
• JDK 7 - added support for ForkJoinPool
• JDK 8 - Introduced lambda and streams.

Concurrency is when two or more tasks execute simultaneously. Concurrency is when two or more tasks can start, run, and complete in overlapping time periods. It doesn't necessarily mean they'll ever both be running at the same instant. For example, multitasking on a single-core machine. Parallelism is when tasks literally run at the same time, e.g., on a multicore processor.