An Introduction to Java Multithreading Concepts

What is Multithreading?

Multithreading is a technique in which multiple tasks run simultaneously within the same program. It allows efficient utilization of CPU by executing multiple threads independently.

Example

Think of a web browser , You can open multiple tabs, and each tab runs independently while still being part of the same browser process.

🔹 Control Flow in Multithreading

In multithreading, we have more than one control flow, meaning multiple tasks can execute at the same time.

Threads can be created using:

• Thread class

• Runnable interface

Creating a Thread

🔹 Using Thread Class:

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

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

🔹Using Runnable Interface:

class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Thread is running...");
    }
}

public class Test {
    public static void main(String[] args) {
        MyRunnable r = new MyRunnable();  
        Thread t = new Thread(r); 
        t.start();  
    }
}

• Java’s Main Thread

  Java starts with one default thread, called the main thread, which runs automatically to execute the main() method of the program.

  🔹 Single-Core vs Multi-Core Environment

  • In a single-core environment, the JVM manages concurrency, switching between threads.

  • In a multi-core environment, the JVM distributes threads across multiple cores for better performance.

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🔹 Thread Life Cycle

In Java, threads officially have five states:

1️⃣ NEW → Thread is created but not started.
2️⃣ RUNNABLE → Thread is ready to run but waiting for CPU execution.
3️⃣ BLOCKED/WAITING → Thread is waiting for some resource or another thread.
4️⃣ TIMED WAITING → Thread is paused for a specific time (sleep(), join(timeout)).
5️⃣ TERMINATED → Thread has completed execution.

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🔹 Important Thread Methods

Here are some essential methods used in multithreading: