Java Concurrency 101

date

Jan 14, 2023

slug

java-concurrency-101

status

Published

Introduction

Java concurrency is the ability of the Java programming language and its runtime environment to execute multiple threads in parallel. Concurrency allows multiple tasks to be executed simultaneously, which can lead to improved performance and responsiveness in your application.

Java provides built-in support for concurrency through the java.util.concurrent package. This package provides a number of classes and interfaces that can be used to create and manage threads, synchronize access to shared resources, and perform other common concurrency-related tasks.

One of the key components of the java.util.concurrent package is the Executor framework. The Executor framework provides a way to create and manage thread pools, which are a group of worker threads that can be used to execute tasks asynchronously.

Here is an example of creating a Thread:

public class MyThread extends Thread {
    public void run() {
        System.out.println("MyThread running");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        myThread.start();
    }
}

The Executor framework also provides a number of other classes and interfaces that can be used to implement common concurrency patterns, such as the CountDownLatch, CyclicBarrier, Semaphore, Exchanger, and Future classes.

Java also provides the synchronized keyword, which allows you to synchronize access to shared resources, and the volatile keyword, which allows you

to indicate that a variable may be modified by multiple threads.

Here is an example of using the synchronized keyword to synchronize access to a shared resource:

public class Counter {
    private int count = 0;
    public synchronized void increment() {
        count++;
    }
}

In this example, the increment() method is marked as synchronized, which means that only one thread can execute this method at a time, even if multiple threads are trying to call it simultaneously.

And here is an example of using the volatile keyword to indicate that a variable may be modified by multiple threads:

public class MyThread extends Thread {
    private volatile boolean stop = false;
    public void run() {
        while (!stop) {
            // do some work
        }
    }
    public void stopThread() {
        stop = true;
    }
}

In this example, the stop variable is marked as volatile, which ensures that all threads see the most up-to-date value of the variable, and any changes made by one thread are immediately visible to other threads.

In summary, Java provides a rich set of concurrency features that can help you write efficient, high-performance, and responsive applications. With the java.util.concurrent package, synchronized keyword and volatile keyword, you have a wide range of tools available to you for implementing concurrency in your Java applications.