Is there a difference between concurrency and parallelism in java?

Question

I have been doing some research in Google and cant quite get my head around the differences (if any) between concurrent and parallel programs in java. Some of the information I

Answer 1

Concurrency is an architectural design pattern, which allows you to run multiple operations at once (which can but dont have to be executed in parallel).

In case of a single core execution of such operations, parallelizm can be "simulated" by for example context switching ( assuming your programming language uses threads for parallel execution).

Lets say you have two threads, in one you enqueue jobs. Second one awaits untill any job exists and picks it up for execution. Despite using a single core processor, both of them are running and communicating (via queue).

This is a concurrent execution - even through threads are executed sequentially on a single core (share it).

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Parallel version of the same exercise would look similar with with one difference:

Execution of threads would happen on a multi-core processor. Threads would be running in parallel to each other and not sequentially (each on his own core).