Difference Between Runnable and Callable in Java

Both Runnable and Callable are interfaces used to create tasks that run in separate threads.
However, Callable is an advanced version introduced to overcome the limitations of Runnable.

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🔹 Runnable Interface

• Present since Java 1.0
• Used to execute a task in a thread
• Cannot return any result
• Cannot throw checked exceptions

Method

public void run();

Example

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

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🔹 Callable Interface

• Introduced in Java 5 (java.util.concurrent)
• Can return a result
• Can throw checked exceptions
• Works with ExecutorService

Method

public V call() throws Exception;

Example

Callable<Integer> task = () -> {
    return 100;
};

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🔹 Key Differences

Feature	Runnable	Callable
Package	java.lang	java.util.concurrent
Method	run()	call()
Return Value	❌ No	✅ Yes
Checked Exceptions	❌ Not allowed	✅ Allowed
Used With	Thread / execute()	ExecutorService / submit()
Result Handling	Not possible	Uses Future

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🔹 When to Use?

✅ Use Runnable when:

• No result is required
• Simple background task

✅ Use Callable when:

• Result is needed
• Exception handling required
• Parallel computations

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