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javamultithreadingrunnable

Scenario where extending thread is preferred than implement Runnable?

As a beginner, I was reading about 2 ways of implementing Multithreading in Java.

I read this thread on SO and on many other threads.

It is stated that

"prefer runnable" , extends thread only when you are specialising Thread's behaviour.

Can someone explain me what is meant by specializing Thread behaviour by providing me a small piece of snippet which help me understand this line.

Solution

  • You should extend a Thread as much as you extend other library classes.

    Take a List for example, more specifically ArrayList, you could add extra behaviour on it, like rejecting a value when adding if a certain predicate fails.
    Then you can call that an PredicatedArrayList.

    It is still a debate whether you want to extend ArrayList here or not, but that debate is not up for this question.

    So an example of extending a thread would be a thread that kills itself after a specific amount of time. Then you would have SuicidingThread extends Thread, which could have a constructor taking the time.

    This even fortifies the argument that you should put your actual tasks in a Runnable.
    Like Runnable somethingRunnable = new SomeClass();, where SomeClass implements Runnable.

    Now you can do either:

    • Thread someThread = new Thread(somethingRunnable);
    • Thread someThread = new SuicidingThread(somethingRunnable, 5, TimeUnit.DAYS);

    So this would be an usecase for extending thread.