Concurrency and Multithreading

Welcome to our lesson on concurrency and multithreading in Java! As a JavaScript developer, you’re familiar with asynchronous programming through callbacks, promises, and async/await. In this lesson, we’ll explore how Java handles concurrent execution and compare it with JavaScript’s approach.

Introduction to Threads in Java

In Java, a thread is the smallest unit of execution within a process. Unlike JavaScript’s single-threaded event loop, Java allows true parallelism with multiple threads running simultaneously on different CPU cores.

// Creating a thread in Java by extending the Thread class
class MyThread extends Thread {
    public void run() {
        System.out.println("Thread is running");
    }
}

// Usage
MyThread thread = new MyThread();
thread.start();

Runnable Interface and Thread Class

Java offers two ways to create threads:

1. Extending the Thread class (as shown above)
2. Implementing the Runnable interface

// Implementing Runnable interface in Java
class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Runnable is running");
    }
}

// Usage
Thread thread = new Thread(new MyRunnable());
thread.start();

This is similar to passing a callback function in JavaScript, but with the added benefit of true parallelism.

Synchronization and the synchronized Keyword

In Java, when multiple threads access shared resources, we need to ensure thread safety. The synchronized keyword is used to create synchronized methods or blocks.

// Java
class Counter {
    private int count = 0;

    public synchronized void increment() {
        count++;
    }
}

JavaScript doesn’t have built-in synchronization mechanisms since it’s single-threaded, but you might use concepts like Promises to manage asynchronous operations.

Executors and Thread Pools

Java provides the Executor framework for managing thread creation and execution. Thread pools are a way to reuse threads for multiple tasks, improving performance.

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

ExecutorService executor = Executors.newFixedThreadPool(5);
executor.submit(() -> System.out.println("Task executed by thread pool"));

In JavaScript, you might use libraries like async for task management, but it’s still based on the event loop:

// JavaScript
import parallelLimit from 'async/parallelLimit';

await parallelLimit(
  [
    (callback) => {
      /* task 1 */
    },
    (callback) => {
      /* task 2 */
    },
  ],
  5,
);
console.log('All tasks completed');

Comparing with JavaScript’s Event Loop

While Java allows true parallel execution with multiple threads, JavaScript uses an event loop for asynchronous operations. Here’s a comparison:

• Java:

  • Multiple threads can run truly in parallel
  • Requires explicit thread management and synchronization
  • Suitable for CPU-intensive tasks

• JavaScript:

  • Single-threaded with an event loop
  • Asynchronous operations are managed through callbacks, promises, or async/await
  • Excellent for I/O-bound tasks

Conclusion

In this lesson, we’ve explored Java’s approach to concurrency and multithreading, drawing comparisons with JavaScript’s asynchronous model. While Java offers more control over parallel execution, it also requires careful management of shared resources. JavaScript’s event loop, on the other hand, provides a simpler model for handling asynchronous operations, but without true parallelism.

In our next lesson, we’ll dive into Java Modules and Package Management, exploring how Java organizes and manages code at a larger scale. We’ll see how this compares to JavaScript’s module system and npm package management. Get ready to learn about Java’s powerful modular system and how it enhances large-scale application development!

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