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Java Thread

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A thread in Java is a lightweight process that runs independently and concurrently with other threads. Java provides built-in support for multithreading, which helps improve performance by executing multiple tasks in parallel.

Creating a Thread in Java:

There are two main ways to create a thread in Java:

Method 1: Extending the Thread Class

  • start() starts a new thread and calls the run() method asynchronously.
  • sleep(500) makes the thread pause for 500ms.
class MyThread extends Thread {
public void run() { // The code inside run() will execute in a separate thread
for (int i = 1; i <= 5; i++) {
System.out.println("Thread: " + i);
try {
Thread.sleep(500); // Pause for 500ms
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

public class Main {
public static void main(String[] args) {
MyThread t1 = new MyThread();
t1.start(); // Start the new thread
}
}

Try it yourself

Method 2: Implementing the Runnable Interface (Recommended):

class MyRunnable implements Runnable {
public void run() {
for (int i = 1; i <= 5; i++) {
System.out.println("Runnable Thread: " + i);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

public class Main {
public static void main(String[] args) {
Thread t1 = new Thread(new MyRunnable());
t1.start(); // Start the thread
}
}

Try it yourself

✅ Why use Runnable instead of Thread?

  • Java supports multiple inheritance via interfaces, not classes.
  • Implementing Runnable is more flexible (allows extending another class if needed).

Thread Methods:

Method

Description

start()

Starts a new thread and calls run() method.

run()

Defines the task to be executed in the thread.

sleep(ms)

Pauses the thread for the specified milliseconds.

join()

Waits for a thread to finish before continuing.

isAlive()

Checks if the thread is still running.

interrupt()

Interrupts a sleeping or waiting thread.

Example: Running Multiple Threads:

class MyThread extends Thread {
public void run() {
for (int i = 1; i <= 3; i++) {
System.out.println(Thread.currentThread().getName() + " - Count: " + i);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

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

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

Try it yourself

Thread Synchronization (Avoiding Race Conditions):

When multiple threads access a shared resource, race conditions may occur. We can prevent this using synchronized methods.

class SharedResource {
synchronized void printNumbers(int n) { // Synchronized method
for (int i = 1; i <= 3; i++) {
System.out.println(Thread.currentThread().getName() + " - " + (n * i));
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

class MyThread extends Thread {
SharedResource obj;
MyThread(SharedResource obj) {
this.obj = obj;
}
public void run() {
obj.printNumbers(2);
}
}

public class Main {
public static void main(String[] args) {
SharedResource obj = new SharedResource();

Try it yourself

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