To assign a task to ExecutorService, we can use the following methods-

execute(Runnable task)

submit(Runnable task) / submit(Callable task)

invokeAny(Collection> tasks)

invokeAll(Collection> tasks)

The Java ExecutorService's execute() method takes in a runnable object and performs its task asynchronously. After making the call to execute method, we call the shutdown method, which blocks any other task to queue up in the executorService. 

https://www.javatpoint.com/java-executorservice