Java - How to 'return' a value in a class -

i trying assign value or return value in class. this:

void setoff() {      boolean onvalue = true;      thread t = new thread(new myclass(onvalue));      system.out.println("on: " + onvalue);  }  class myclass implements runnable{      public boolean on;      public myclass (boolean _on) {          on = _on      }      public run() {          on = false;      }  } 

is possible? thanks!

it possible, need change code bit. check following classes:

• callable<v>
• futuretask<v>

the first 1 runnable, method need implement defined v call() throws exception, instead of void run(): allows return value.

the second 1 wraps callable<v> (or runnable plus constant return value), , runnable itself, can pass thread doing runnable.

so, change code following:

void setoff() {   final futuretask<boolean> ft = new futuretask<boolean>(new myclass());   new thread(ft).start();   try {     system.out.println("the result is: " + ft.get());   } catch (executionexception e) {     system.err.println("a method executed on background thread has thrown exception");     e.getcause().printstacktrack();   } }  class myclass implements callable<boolean> {   @override public boolean call() throws exception {     // let's fake long running computation:     thread.sleep(1000);     return true;   } } 

the call ft.get() return after call() method finishes executing (on background thread), have wait 1 second before line gets printed console.

there many other useful methods on futuretask. check the documentation.

there other classes may find useful: executorservice , implementations, , factory methods in executors. has method called submit accepts runnable or callable<v>, , returns future<?> or future<v>, 1 of interfaces implemented futuretask. similar behaviour. example:

public static void main() {   final executorservice es = executors.newcachedthreadpool();   final future<boolean> f = es.submit(new myclass());   try {     system.out.println("the result is: " + f.get());   } catch (executionexception e) {     system.err.println("a method executed on background thread has thrown exception");     e.getcause().printstacktrack();   }   es.shutdown(); } 

the advantage of executorservice manage threads you. may create threads , reuse them callables , runnables submit: possibly improve performance if have many such jobs, since avoid creating 1 thread per job -- thread creation has overhead!

edit: .get() method throws executionexception, wraps exception might thrown during execution of .call() method. inspect exception, catch executionexception , call .getcause() on it. i've added missing try/catch block.