Explain throw vs throws in Java

Q: What is the difference between throw and throws?

throw is used to throw an exception, throws declares exceptions a method might throw.

💡 Concept: throw vs throws

The throw and throws keywords in Java are related to exception handling but serve different purposes.

📘 Quick Intro

throw is used to explicitly throw an exception, whereas throws declares that a method can throw one or more exceptions.

🧠 Analogy

Think of throw as tossing a ball (exception) and throws as a warning sign indicating the ball might be thrown.

🔧 Technical Explanation

throw is used inside method body to throw an exception object.
throws is used in method signature to declare exceptions the method might throw.
throw throws a single exception object.
throws can declare multiple exceptions separated by commas.
Using throws informs caller about possible exceptions.

🎯 Use Cases

✅ Use throw to manually trigger an exception.
✅ Use throws to delegate exception handling to caller.
✅ Improve code clarity and exception propagation.

💻 Java throw vs throws Example


public void checkAge(int age) throws Exception {
    if (age < 18) {
        throw new Exception("Age must be 18 or older");
    }
}

public void demo() {
    try {
        checkAge(15);
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

❓ Interview Q&A

Q1: What is the difference between throw and throws?
A: throw is used to throw an exception, throws declares exceptions a method might throw.

Q2: Can a method have multiple exceptions in throws?
A: Yes, separated by commas.

Q3: Can throw be used outside method?
A: No.

Q4: Is throws mandatory?
A: Only for checked exceptions.

Q5: Can throw throw multiple exceptions?
A: No, only one at a time.

Q6: Does throws handle exceptions?
A: No, it declares.

Q7: Is throw a keyword or method?
A: Keyword.

Q8: Can throws be used with runtime exceptions?
A: Yes, but optional.

Q9: What happens if exception is not caught?
A: It propagates.

Q10: Can throw be inside try block?
A: Yes.

📝 MCQs

Q1. What is the difference between throw and throws?

throw throws an exception, throws declares exceptions
throw declares exceptions, throws throws exception
Both are same
None

Q2. Can a method have multiple exceptions in throws?

No
Yes
Sometimes
Only one

Q3. Can throw be used outside method?

Yes
No
Sometimes
Only in Java 9

Q4. Is throws mandatory?

Always
Only for checked exceptions
Never
Sometimes

Q5. Can throw throw multiple exceptions?

Yes
No
Sometimes
Only in Java 11

Q6. Does throws handle exceptions?

Yes
No
Sometimes
Only in Java 9

Q7. Is throw a keyword or method?

Method
Keyword
Class
Object

Q8. Can throws be used with runtime exceptions?

No
Yes
Sometimes
Only checked

Q9. What happens if exception is not caught?

It is ignored
It propagates
Program crashes
Handled by JVM

Q10. Can throw be inside try block?

No
Yes
Sometimes
Only in Java 8

💡 Bonus Insight

Using throw and throws properly improves exception clarity and control flow in Java.

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