Multi Thread Example using Execution Service

import java.util.List;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Future;

import static java.util.Arrays.asList ;

public class ExecutorServiceMultiThreadSubstraction

{    

    static class Substract implements Callable<Long> {

        private long b;

        private long a;

        Substract(long a, long b){

            this.a = a ;

            this.b = b ;

        }

        @Override

        public Long call() throws Exception

        {

            return a-b;

        }

        

        public static void main(String str[]) throws Exception{

            ExecutorService executor = Executors.newFixedThreadPool(5) ;

            List<Future<Long>> results = executor.invokeAll(asList(new Substract(0,10), new Substract(11,13), new Substract(14,15) )) ;            

            executor.shutdown() ;            

            for(Future<Long> result: results)

                System.out.println(result.get()) ;

        }

    }

}

Thread safe Singleton Design Pattern Java Implementation

public class SingletonClass{
private static SingletonClass instance = null;
private SingletonClass() { }
public static synchronized SingletonClass getInstance() {
if (instance == null) {
instance = new SingletonClass();
}
return instance;
}
}

What is CountDownLatch

CountDownLatch is a versatile synchronization tool.

- It Allows one or more threads to wait until a work is done in other threads
- Used as on/off latch or gate
- Threads invoking await() method waits at the gate
- The count cannot be reset
- TO reset the count, you may check with CyclicBarrier
- Useful property is that it doesn't require that threads calling countDown wait for the count to reach zero before proceeding