Threads in Java

Question

What is the difference between threads in java and native threads?

Answer 1

Java threads can be implemented in any way that conforms to the specification. The specification doesn't require a specific implementation.

Effectively all modern desktop and/or server JVMs implement Java threads as native threads. That means that there is exactly 1 native thread for each Java thread and that the operating system does all the scheduling, just as it does for a C program, for example.

Some old JVMs and possibly some JVMs for devices with limited resources might implement threads in a way where the number of native threads used is smaller than the number of Java threads running (or possibly 1). Those implementations are said to implement so called "green threads". In this case the JVM itself is responsible for task switching and scheduling, as opposed to delegating that task to the operating system.

Answer 2

It depends on the implementation of the JVM, of course, but I think they are the same. It is, a Thread in Java is implemented via a native thread. You can expect/do with Java threads all kind of things you can with native threads.