Interview question

What are the ways to create threads in Java? Explain Thread class vs Runnable. Java में threads बनाने के तरीके कौन से हैं? Thread class vs Runnable explain करें।

Answer

Threads can be created in two ways: extending Thread class or implementing Runnable interface. Runnable is preferred as Java doesn't support multiple inheritance. Both approaches have different advantages.

Method	Syntax	Advantages	Disadvantages
Thread Class	class MyThread extends Thread	Direct access to Thread methods	Can't extend other class
Runnable Interface	class MyRun implements Runnable	Can extend another class	Need Thread wrapper

// Method 1: Extending Thread class
public class MyThread extends Thread {
    public void run() {
        System.out.println('Thread is running');
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.start();  // Don't call run() directly
    }
}

// Method 2: Implementing Runnable (PREFERRED)
public class MyRunnable implements Runnable {
    public void run() {
        System.out.println('Runnable is running');
    }
}

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

// Method 3: Lambda expression (Java 8+)
new Thread(() -> {
    System.out.println('Lambda thread');
}).start();

// Method 4: Anonymous class
new Thread(new Runnable() {
    public void run() {
        System.out.println('Anonymous thread');
    }
}).start();

// Important: Always call start(), never run()
// start() creates new thread and calls run()
// run() executes in same thread
t.start();  // Correct
t.run();    // Wrong - doesn't create new thread

Threads बनाने के तरीके:

1. Thread class extend करना:
public class MyThread extends Thread {
    public void run() { }
}
MyThread t = new MyThread();
t.start();

2. Runnable implement करना (BEST):
public class MyRun implements Runnable {
    public void run() { }
}
Thread t = new Thread(new MyRun());
t.start();

3. Lambda (Java 8+):
new Thread(() -> {
    // code
}).start();

Important: start() करो, run() नहीं!

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