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readme.md

☕ Java Lesson – join() in Multithreading

Is lesson me hum seekhenge:

  • Multithreading basics
  • join() method kya hota hai
  • join() ka use kyun hota hai
  • join() ka working
  • Real examples

1️⃣ Multithreading Kya Hota Hai?

Multithreading ka matlab:

ek program me multiple threads ka parallel execution

Example:

music play + download + UI response same time

2️⃣ Thread Class

Java me thread banane ke 2 tarike:

1. Thread class extend karke
2. Runnable interface implement karke

3️⃣ join() Method Kya Hota Hai?

join() method ka use hota hai:

ek thread ko wait karne ke liye jab tak dusra thread complete na ho jaye

4️⃣ Syntax

thread.join();

5️⃣ Basic Example

class Test extends Thread {

    public void run(){
        for(int i = 1; i <= 3; i++){
            System.out.println("Thread running: " + i);
        }
    }

    public static void main(String[] args) throws Exception {

        Test t1 = new Test();

        t1.start();

        t1.join(); // main thread wait karega

        System.out.println("Main thread finished");
    }
}

6️⃣ Without join()

t1.start();

System.out.println("Main thread finished");

Output unpredictable hoga:

Main thread pehle print ho sakta hai

7️⃣ With join()

t1.start();
t1.join();

Output:

thread complete hone ke baad hi next line execute hogi

8️⃣ Multiple Threads Example

class Test extends Thread {

    public void run(){
        System.out.println(Thread.currentThread().getName());
    }

    public static void main(String[] args) throws Exception {

        Test t1 = new Test();
        Test t2 = new Test();

        t1.start();
        t1.join(); // t1 complete

        t2.start(); // fir t2 start
    }
}

9️⃣ join() Variants

t1.join();          // complete hone tak wait
t1.join(1000);      // max 1 second wait
t1.join(1000, 500); // nanoseconds bhi

🔟 Real-Life Analogy

Project me:
Task A complete hone ke baad hi Task B start ho

1️⃣1️⃣ Important Points

✔ join() thread coordination ke liye use hota hai
✔ InterruptedException handle karna padta hai
✔ execution order control kar sakte hain


1️⃣2️⃣ join() vs sleep()

Feature join() sleep()
Purpose wait for another thread pause current thread
Dependency dusre thread par khud par

🎯 Interview Questions

  1. join() method kya hota hai?
  2. join() aur sleep() me difference?
  3. kya join() multiple threads me use hota hai?
  4. join() bina try-catch kyun nahi chal sakta?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Multithreading basics
✔ join() method
✔ execution control
✔ practical examples

join() Java me thread synchronization aur execution order control ke liye use hota hai.