ExecutorService in laymans terms

>>>executor.submit(new Callable<Boolean>() {
              public Boolean call() throws Exception { return doTaskWork(); }}) ;


submit takes Callable paramter and returns Future . not sure what these mean.
can you give a simple example.

thx

also in what situations do i use callable v/s runnable

executor.submit(new Callable<Boolean>() {
              public Boolean call() throws Exception { return doTaskWork(); }}) ;

v/s

executor.submit(Runnable task)

thx

The simplest form is you just submit a Runnable task.  In that case it's "fire and forget".  You submit the task and it will run later.  This is fine if you just want to start a thread to do some work, don't really care when it runs or are interested in getting the result of the run.  (A typical example might be to handle a http request in a web server.  You just need the work done and the result will go back to the sender of the request).

If you submit a callable, the Future object allows you to examine how it will behave in the future:

Future<Boolean> future = executor.submit(new Callable<Boolean>() {
              public Boolean call() throws Exception { return doTaskWork(); }}) ;

This gives you more control and insight into when this task runs.  You can now call:

future.isDone() ;

to find out if it's finished yet.

You can also call:

Boolean result = future.get() ;

to block and wait for the task to finish and get the result of the method.  (It's a boolean here because I defined Callback<Boolean>.  You can return anything you want).  What's really nice is this also will throw an exception if the underlying method threw an exception.  This is often a problem with threads - if they throw an exception it's hard to signal that to the person who started the thread.  This lets you solve that).

Hope that helps,

Doug

>>>Future<Boolean> future = executor.submit(new Callable<Boolean>() {
              public Boolean call() throws Exception { return doTaskWork(); }}) ;
This gives you more control and insight into when this task runs.  You can now call:
future.isDone() ;

Cant i do the above using a Runnable task? what i am trying to understand is
submit(Callable<T> task)  returns a Future
submit(Runnable task)  returns a Future
so how are they different?
can you show me with a simple example?

thanks

Callable returns something, Runnable doesn't
Callable was a later addition

http://geekexplains.blogspot.com/2008/05/callable-interface-vs-runnable.html

If you don't care what the result of running the task is you can use Runnable.  This is like a simple thread.

If you want the result of the task you should use Callable.