Inline runnable with constructor?

Question

I'm looking to use a thread to process something in the background. Since this code isn't used anywhere else & is not complex I'd like to use an inline function. However the function needs a copy of an attribute at the time the thread was created i.e.: I'd like it if the output from the following example 'true' instead of 'false'

public class InlineThreadTest {
    boolean value;

    public static void main(String[] args) {
        new InlineThreadTest();
    }   

    InlineThreadTest() {    
        value = true;
         java.util.concurrent.Executors.newSingleThreadExecutor().execute(new Runnable() {
            @Override 
            public void run() {
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {}         
                System.out.println(value);
            }
        });
        value = false;
    }
}

... I can do what I'm looking to do by creating a separate class that implements Runnable, but having this inline seems like something that might be good.

I had a look @ https://stackoverflow.com/a/362443/64696 , but cannot figure out how to mold this to my use case.

Have `final boolean valueRightNow = value` in your `InlineThreadTest` method and access `valueRightNow` instead of `value` inside of your `run` method. That's a very straight-forward application of the linked-to answer, I don't see what the problem is. — Joachim Sauer, Sep 17 '19 at 15:35
FYI: what you're calling "inline function" actually is an _anonymous inner class_. The expression `new Runnable() {...}` declares a class that implements `Runnable`, and each time your program executes that expression, it creates a new instance of the class. — Solomon Slow, Sep 17 '19 at 15:39
You can also use `ThreadLocal` if you want a thread scoped variable. — Jason, Sep 17 '19 at 15:49

score 1 · Answer 1 · answered Sep 17 '19 at 16:47

Runnable implementation is a thread and thread won't return any value. The ExecutorService.execute method just runs the thread and you have no way to get the state of the thread whether it was executed or not. If you want to check for the task (not thread) executed by ExecutorService you should use Callable and work with sumbit(). Your modified example:

public class InlineThreadTest {
boolean value;

public static void main(String[] args) {
    new InlineThreadTest();
}   

InlineThreadTest() {  
    value = true;
    java.util.concurrent.Future<Boolean> f =
     java.util.concurrent.Executors.newSingleThreadExecutor().submit(new Callable<Boolean>() {
         public Boolean call() {
           System.out.println(value);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {}
            value = false;
            return value;
        }
    });
    try {
      System.out.println(f.get()+" or value="+value);
    } catch (Exception ex) { }
}

}

You'll get 2 lines

true
false or value=false

Inline runnable with constructor?

1 Answers1