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MultiThreadWithCallable.java
MultiThreadWithCallable.java
 
 
PrintTask.java
PrintTask.java
 
 
TestingFuture.java
TestingFuture.java
 
 
readme.md
readme.md
 
 

readme.md

☕ Java Lesson – Executor Returning Future in Java

Is lesson me hum seekhenge:

  • Future kya hota hai
  • Executor ka result kaise return hota hai
  • Callable vs Runnable
  • Future methods
  • Practical examples

1️⃣ Problem – Runnable Limitation

Runnable me:

return value nahi hoti ❌

Example:

Runnable task = () -> {
    System.out.println("Task done");
};

👉 result return nahi hota

2️⃣ Solution – Callable

Callable use karte hain:

jab result return karna ho ✔

3️⃣ Callable Interface

Callable<Integer> task = () -> {
    return 10 + 20;
};

✔ return value hoti hai
✔ exception throw kar sakta hai

4️⃣ Future Kya Hota Hai?

Future ek object hai jo:

future result ko represent karta hai

👉 matlab:

result baad me milega

5️⃣ Basic Example (Executor + Future)

import java.util.concurrent.*;

class Test {

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

        ExecutorService executor = Executors.newSingleThreadExecutor();

        Callable<Integer> task = () -> {
            Thread.sleep(1000);
            return 50;
        };

        Future<Integer> future = executor.submit(task);

        System.out.println("Task submitted...");

        int result = future.get(); // wait karega

        System.out.println("Result: " + result);

        executor.shutdown();
    }
}

6️⃣ Flow Samjho

submit() → Future milega
Future → get() → result milega

7️⃣ Future Important Methods

Method Use
get() result lena
isDone() check complete
cancel() task cancel
isCancelled() cancel check

8️⃣ Non-Blocking Check Example

while(!future.isDone()){
    System.out.println("Waiting...");
}

System.out.println(future.get());

9️⃣ Multiple Tasks Example

ExecutorService executor = Executors.newFixedThreadPool(2);

Callable<Integer> task1 = () -> 10;
Callable<Integer> task2 = () -> 20;

Future<Integer> f1 = executor.submit(task1);
Future<Integer> f2 = executor.submit(task2);

System.out.println(f1.get() + f2.get());

executor.shutdown();

🔟 Difference – Runnable vs Callable

Feature Runnable Callable
Return ❌ No ✔ Yes
Exception ❌ No ✔ Yes
Use execute() submit()

1️⃣1️⃣ Blocking Nature ⚠

future.get();

✔ wait karta hai jab tak result ready na ho

1️⃣2️⃣ Real-Life Analogy

Food order:
order diya → Future
food ready → get()

1️⃣3️⃣ Important Points

✔ Callable result return karta hai
✔ Future async result handle karta hai
✔ get() blocking hota hai
✔ always executor shutdown karo

🎯 Interview Questions

  1. Future kya hota hai?
  2. Runnable vs Callable difference?
  3. future.get() blocking kyun hota hai?
  4. Future cancel kaise karte hain?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Future concept
✔ Callable usage
✔ Executor + Future flow
✔ Async result handling

Executor + Future Java me asynchronous programming ka powerful combination hai.