Java.util.concurrent.Executor interface with Examples

The concurrent API in Java provides a feature known as an executor that initiates and controls the execution of threads. As such, an executor offers an alternative to managing threads using the thread class. At the core of an executor is the Executor interface. It refers to the objects that execute submitted Runnable tasks. 

Class hierarchy:

java.util.concurrent
  ↳ Interface Executor

Implementing Sub-Interfaces:

ExecutorService
ScheduledExecutorService

Implementing Classes:

AbstractExecutorService
ForkJoinPool
ScheduledThreadPoolExecutor
ThreadPoolExecutor

Methods in Executor interface:

1. execute(): This function executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the Executor implementation.
   Syntax:

void execute(Runnable task)

Example to demonstrate an Executor.

Java

import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;

public class ExecutorDemo {
    public static void main(String[] args)
    {
        ExecutorImp obj = new ExecutorImp();
        try {
            obj.execute(new NewThread());
        }
        catch (RejectedExecutionException
               | NullPointerException exception) {
            System.out.println(exception);
        }
    }
}

class ExecutorImp implements Executor {
    @Override
    public void execute(Runnable command)
    {
        new Thread(command).start();
    }
}

class NewThread implements Runnable {
    @Override
    public void run()
    {
        System.out.println("Thread executed under an executor");
    }
}

Output:

Thread executed under an executor

Reference:https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/Executor.html