What is the difference between Java concurrency and parallelism?

Concurrency and parallelism in Java are two distinct concepts, but they are often confused with each other. The difference between them is as follows:

1. Concurrency refers to the simultaneous execution of multiple independent tasks in a program, which may alternate within the same time frame. In Java, concurrency can be achieved by using threads to schedule the execution of tasks alternately.
2. Concurrency: Concurrency refers to the execution of multiple independent tasks simultaneously in a program, with these tasks running on different processors to achieve true parallel execution. In Java, you can use multi-threading technology to implement concurrency and leverage multi-core processors to execute multiple threads simultaneously.

In general, concurrency refers to multiple tasks executing alternately, while parallelism refers to multiple tasks executing simultaneously. In Java, although concurrency and parallelism can be achieved, true parallelism requires utilizing multi-core processors.