将方法提交到ExecutorService Java

Question

So I have this code here, that adds my "NamePrinter" runnable class as ExecutorService tasks. Everything works fine, but I'd like to get rid of that extra class. So I am asking is there a way to submit method to ExexutorService?

Here is the code that I currently have:

public void start(){
        Collection<Future<?>> futures = new LinkedList<>();
        final ExecutorService es = Executors.newFixedThreadPool(poolSize);

        for (int i = 0; i < 10; i++) {
        futures.add(es.submit(new NamePrinter(name)));
        }

        es.shutdown();
}

But I'd like it to be something like this:

public void start(){
            Collection<Future<?>> futures = new LinkedList<>();
            final ExecutorService es = Executors.newFixedThreadPool(poolSize);

            for (int i = 0; i < 10; i++) {
            futures.add(es.submit(namePrint(i+"name"))); // This code doesn't work, I just made it so you could understand what I mean.
            }

            es.shutdown();
    }

public void namePrint(String name){  // I'd like this to be the task that ExecutorService runs.

System.out.println(name);

}

Is this something that is possible to achieve?

Answer 1

The closest you can come as an anonymous inner class:

for (int i = 0; i < 10; i++) {
    final int x = i;
    futures.add(es.submit(new Runnable() {
        @Override public void run() {
            namePrint(x + "name");
        }
    }));
}

Answer 2

You are essentially asking: is Java supporting functions as first class citizens (sometimes it is refered as closures or lambdas ) - no, you can't do this in Java . You can in Groovy, Scala, JavaScript, C#... but not in Java.

Your NamePrinter class (probably implementing Runnable or Callable ) is the closest you can get in Java and this is the Java way (or you can use anonymous inner class).

Answer 3

In this specific case, I think you'll not be able to do exactly what you want, because the run method of Runnable interface doesn't take any arguments. However, you can use lambda expressions since Java 8 . So you have few options now:

1 - Define the method on-the-fly

final String name = "whatever";

exServ.execute(() -> {            
    System.out.println(name);
});

2 - Define a static method and then use static method reference

public static void printName()
{
    System.out.println(ClassNameX.name);
}

exServ.execute(ClassTest::printName);

3 - Create an instance of your NamePrinter class - which doesn't need to implement the Runnable interface - to store the parameters and then use instance method reference.

NamePrinter np = new NamePrinter("testName");

exServ.execute(np::namePrint);

Answer 4

There are some options for this:

1. Using anonymous class

    es.submit { new Runnable() { public void run() { //do your stuff here } }); 

2. Use languages which support closures like Scala . However the API must support this, which ExecutorService doesn't.

3. Wait for Java 8 which will introduce closures.