Which of the following is a valid identifier in Java? a. 123identifier b. _identifier c. #identifier d. identifier-123

To determine which of the given options is a valid identifier in Java, let's analyze each option based on Java's rules for naming identifiers.

Analysis of Options

1. 123identifier: Invalid. Identifiers cannot start with a digit.
2. _identifier: Valid. Identifiers can start with an underscore.
3. #identifier: Invalid. Identifiers cannot contain special characters like #.
4. identifier-123: Invalid. Identifiers cannot contain hyphens - as they are interpreted as the subtraction operator.

Conclusion

The only valid identifier from the options provided is _identifier.

Final Answer

The valid identifier in Java is _identifier.