Java Multithreading Explained — Concepts, Examples & Best Practices
Modern applications handle multiple users at the same time.
To achieve this efficiently, programs must run tasks concurrently.
In Java (programming language), multithreading allows a program to execute multiple parts simultaneously, improving performance and responsiveness.
This guide explains threads, synchronization, thread pools, and real use-cases.
📌 What is Multithreading?
A thread is a lightweight unit of execution inside a process.
Instead of running tasks sequentially:
Task1 → Task2 → Task3
They can run in parallel:
Task1
Task2
Task3
🖼️ Multithreading vs Single Thread
Creating Threads in Java
1️⃣ Using Thread Class
class MyThread extends Thread {
public void run() {
System.out.println("Thread running: " + Thread.currentThread().getName());
}
}
public class Main {
public static void main(String[] args) {
MyThread t1 = new MyThread();
t1.start();
}
}
2️⃣ Using Runnable Interface (Preferred)
class Task implements Runnable {
public void run() {
System.out.println("Task executed by: " + Thread.currentThread().getName());
}
}
public class Main {
public static void main(String[] args) {
Thread t1 = new Thread(new Task());
t1.start();
}
}
3️⃣ Using Lambda
new Thread(() -> {
System.out.println("Lambda thread running");
}).start();
Thread Lifecycle
States:
NEW
RUNNABLE
BLOCKED
WAITING
TERMINATED
🖼️ Thread Lifecycle
Synchronization Problem (Race Condition)
Multiple threads modify same data.
class Counter {
int count = 0;
void increment() {
count++;
}
}
Wrong result due to race condition.
Fix using synchronized
synchronized void increment() {
count++;
}
🖼️ Race Condition
Thread Communication
Using wait/notify:
synchronized(lock){
lock.wait();
lock.notify();
}
Thread Pools (ExecutorService)
Creating many threads is expensive.
Use thread pools:
ExecutorService executor = Executors.newFixedThreadPool(3);
executor.submit(() -> {
System.out.println("Task executed");
});
executor.shutdown();
🖼️ Thread Pool
Deadlock Example
synchronized(lock1){
synchronized(lock2){
}
}
Another thread locks in reverse order → deadlock.
Best Practices
✔ Prefer Runnable / ExecutorService
✔ Avoid shared mutable data
✔ Use synchronization carefully
✔ Always shutdown executors
✔ Use immutable objects
When to Use Multithreading
| Scenario | Benefit |
|---|---|
| API handling | Parallel requests |
| File processing | Faster I/O |
| Background tasks | Non-blocking UI |
| Batch jobs | Performance |
📚 Recommended Reading
🎯 Conclusion
Multithreading improves performance but introduces complexity.
Correct synchronization and thread management are essential for stable applications.
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