使用Runnable VS的单个实例创建多个线程。 每个线程都有单独的实例

Question

What is the difference between creating multiple threads with one instance of Runnable for all of them AND with separate instances for each thread. When should I use the first approach and when the second one? Can you give me an example so I can comprehend the two concepts more clearly? I found few similar topics, but I could not entirely understand the contrast between both of the two approaches.

Answer 1

You can only use the same Runnable across multiple thread if each thread is exactly the same. This is rarely useful. You could have threads in a thread pool work this way, but in this case I would use the built in thread pools, not write your own.

If you need different threads to have a different state, you will need a different Runnable for each Thread as the Runnable holds the state. This is useful when you have threads which need to work on different data even though the code might be the same.

Answer 2

What's the difference...?

The difference---the entire difference---is that if the Runnable class has one or more fields , then those fields will be shared by the several threads if all of the threads are given the same instance, and they will not be shared if each thread is given its own instance.

If the Runnable class does not declare any fields, then there effectively is no difference at all.

Basically, it's up to you to decide which data in your program should be shared between threads and which data should not be shared.

If all of the Runnable fields are shared, (ie, if you use the same Runnable instance for every thread), then that will make it harder for you to have any data that are not shared.