Lambda Expressions | Concurrent Programming Approach 4

Last Updated : 08 Apr, 2019

Prerequisite: Different Approaches to Concurrent Programming in Java Lambda expressions are very similar in behaviour to anonymous inner classes. They have complete access to code from surrounding classes including the private data. They are much more concise, succinct and readable. However, lambda expressions cannot have instance variables, so they do not maintain a state. We can replace Anonymous Inner Class with Lambda Expression as follows: Anonymous Inner Class:

    Thread thread = new Thread(new Runnable() {
      @Override
      public void run() {
        System.out.println("Printed inside Anonymous Inner Class!");
      }
    });

Lambda Expression:

Thread anotherThread = new Thread(() -> System.out.println("Printed inside Lambda!"));

Practical Implementation:

Java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

// Code for Concurrent programming using
// Lambda Expression
public class MyClass {

    // Driver method
    public static void main(String[] args)
    {
        new MyClass().startThreads();
    }

    // Starting threads with pool size as 2
    private void startThreads()
    {
        ExecutorService taskList
            = Executors.newFixedThreadPool(2);

        for (int i = 0; i < 5; i++) {

            int finalI = i + 1;

            // Prints thread name and value
            // of the counter variable
            taskList.execute(() -> {

                for (int j = 0; j < finalI; j++) {

                    System.out.println(
                        Thread
                            .currentThread()
                            .getName()
                        + " Counter:" + j);
                    pause(Math.random());
                }
            });
        }
        taskList.shutdown();
    }

    // Pauses execution allowing time for
    // system to switch back and forth
    private void pause(double seconds)
    {
        try {
            Thread.sleep(
                Math.round(1000.0 * seconds));
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Output:


pool-1-thread-1 Counter:0
pool-1-thread-2 Counter:0
pool-1-thread-2 Counter:1
pool-1-thread-2 Counter:0
pool-1-thread-1 Counter:0
pool-1-thread-2 Counter:1
pool-1-thread-1 Counter:1
pool-1-thread-2 Counter:2
pool-1-thread-1 Counter:2
pool-1-thread-2 Counter:0
pool-1-thread-1 Counter:3
pool-1-thread-2 Counter:1
pool-1-thread-2 Counter:2
pool-1-thread-2 Counter:3
pool-1-thread-2 Counter:4

Advantages: The user can easily access data in the main class including the private data. Lambdas are concise, succinct and readable. Disadvantages: Lambdas are not allowed to have instance variables, thus we cannot pass arguments to run method. Also, we typically use lambdas when we have some shared data which invites the danger of race conditions.