Multithreading in Java: A Practical Guide

Introduction

Applications must manage several tasks at once in the fast-paced digital environment of today to guarantee efficiency and responsiveness. Java’s multithreading feature enables programmers to run numerous threads at once, increasing the speed and effectiveness of applications.

In this manual, we will look at:

The definition of multithreading and its significance
How multithreading is implemented in Java
Thread states and lifecycle
Thread safety and synchronization
The best ways to use Java multithreading

What is Multithreading?

Java’s multithreading functionality lets an application operate several threads simultaneously. Lightweight subprocesses that run independently yet share resources with other threads are called threads.

Multithreading advantages include:

Enhanced Efficiency: The ability to run many threads concurrently results in a speedier application.
Better Use of Resources: Threads effectively share system resources and memory.
Better Responsiveness: UI programs maintain their responsiveness even when they are executing background operations.
CPU Utilization Efficiency: A number of CPU cores are used efficiently.

Implementing Multithreading in Java

There are two primary ways to create threads in Java:

1. Extending the `Thread` Class

class MyThread extends Thread {
    public void run() {
        for (int i = 1; i <= 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - Count: " + i);
        }
    }
}

public class ThreadExample {
    public static void main(String[] args) {
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();

        t1.start();
        t2.start();
    }
}

2. Implementing the `Runnable` Interface

class MyRunnable implements Runnable {
    public void run() {
        for (int i = 1; i <= 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - Count: " + i);
        }
    }
}

public class RunnableExample {
    public static void main(String[] args) {
        Thread t1 = new Thread(new MyRunnable());
        Thread t2 = new Thread(new MyRunnable());

        t1.start();
        t2.start();
    }
}

Using Runnable is preferred as it allows extending other classes while still implementing multithreading.

Thread Lifecycle in Java

A thread in Java goes through the following states:

A new thread has been established, but it has not yet begun.
Runnable: The thread is awaiting CPU time but is prepared to run.
Running: The thread is presently in operation.
A blocked thread is one that is awaiting a resource.
Waiting: A thread waits endlessly for a signal from another thread.
Timed Waiting: A thread waits for a predetermined amount of time.
Terminated: The thread has finished running.

Synchronization in Multithreading

When multiple threads access shared resources, race conditions and inconsistencies may occur. Synchronization ensures only one thread accesses the resource at a time.

Using `synchronized` Keyword

class SharedResource {
    synchronized void printNumbers(int n) {
        for (int i = 1; i <= 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - " + (n * i));
        }
    }
}

class MyThread extends Thread {
    SharedResource sr;
    MyThread(SharedResource sr) {
        this.sr = sr;
    }
    public void run() {
        sr.printNumbers(5);
    }
}

public class SyncExample {
    public static void main(String[] args) {
        SharedResource obj = new SharedResource();
        MyThread t1 = new MyThread(obj);
        MyThread t2 = new MyThread(obj);
        
        t1.start();
        t2.start();
    }
}

Using `Lock` from `java.util.concurrent`

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class SharedResource {
    private final Lock lock = new ReentrantLock();
    
    void printNumbers(int n) {
        lock.lock();
        try {
            for (int i = 1; i <= 5; i++) {
                System.out.println(Thread.currentThread().getName() + " - " + (n * i));
            }
        } finally {
            lock.unlock();
        }
    }
}

Best Practices for Multithreading in Java

Minimize Shared Resources: To prevent race circumstances, cut down on the number of shared variables.

Use Thread Pools: Use ExecutorService to create numerous threads rather than doing it by hand.
Make sure the resource locking order is correct to prevent deadlocks.
Choose Runnable Over Thread Class: Encourages greater flexibility and design.
Use Concurrent Collections: For thread safety, use ConcurrentHashMap and CopyOnWriteArrayList.
Limit Thread Creation: Having too many threads can actually make performance worse.

Conclusion

Multithreading in Java is a powerful tool that enables efficient execution of tasks in parallel, improving performance and responsiveness. By following best practices, synchronizing shared resources, and leveraging Java’s built-in concurrency utilities, you can build high-performance multithreaded applications with confidence.

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