Explain throw vs throws in Java
💡 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
throwis used inside method body to throw an exception object.throwsis used in method signature to declare exceptions the method might throw.throwthrows a single exception object.throwscan declare multiple exceptions separated by commas.- Using
throwsinforms caller about possible exceptions.
🎯 Use Cases
- ✅ Use
throwto manually trigger an exception. - ✅ Use
throwsto 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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