How to assign a variable in a different thread

Question

I have the following method:

 public boolean isMatch(List<T> sources, String captured) {
      boolean isMatch = false;
      return isMatch;
 }

I need to start a new thread inside it like below:

Runnable r = new Runnable() {
        public void run() {
            VERIFY();
        }
    };
    Thread s = new Thread(r);
    s.start();

The thread is supposed to perform some operations. When it finishes, I need to assign the return boolean value to the isMatch variable. How do I do this?

how are you planning on calling the method, how (and when) is the caller to be informed about the outcome? — luk2302, Sep 24 '18 at 09:07
since `isMatch` is a _local_ variable no code can't change it from the outside. Besides that, wouldn't the `isMatch(...)` method need to calculate the value based on the parameters anyway? — Thomas, Sep 24 '18 at 09:07
@luk2302 the method is called in a different method and the boolean result is required — Ikiugu, Sep 24 '18 at 09:09
If you want to wait for thread to complete then please use callable instead of runnable. Runnable cannot return value but callable interface can return value. — Mahesh, Sep 24 '18 at 09:10
@Thomas the parameters at this point are ignored. All that is required is that once we get into the method, we run the Verify method and based on the return value, we return it in the isMatch method — Ikiugu, Sep 24 '18 at 09:10
@luk2302 i need to use a new thread because the operations being done with the VERIFY method will block the UI — Ikiugu, Sep 24 '18 at 09:12
then you need to drop the return value and use a callback instead. — luk2302, Sep 24 '18 at 09:12
I'd see 2 possibilities: use a future and periodically check it or pass some function/object that can be called to put the value somewhere. — Thomas, Sep 24 '18 at 09:16

score 1 · Accepted Answer · answered Sep 24 '18 at 09:25

1

Since you need a return value, you should use the interface Callable<T> instead of Runnable. Look at what the docs say:

The Callable interface is similar to Runnable, in that both are designed for classes whose instances are potentially executed by another thread. A Runnable, however, does not return a result and cannot throw a checked exception.

Note that a Callable is submitted through an ExecutorService.

answered Sep 24 '18 at 09:25

Talendar

1,841
14
23

Thanks. Let me look into this – Ikiugu Sep 24 '18 at 10:06
You are welcome! If this answers your question, please mark this answer as accepted. – Talendar Sep 24 '18 at 18:51

How to assign a variable in a different thread

1 Answers1