Java Identifiers

Java Identifiers – Complete Guide

In Java Identifiers is the name given to:

• variables

• methods

• classes

• objects

• packages

 Identifiers help Java identify program elements.

 1. Examples of Java Identifiers

Here:

• age, salary, name → variable identifiers

• calculateTotal → method identifier

• Student → class identifier

 2. Rules for Java Identifier (Very Important)

 Allowed

1. Can contain letters (a–z, A–Z)

2. Can contain digits (0–9)

3. Can contain underscore (_)

4. Can contain dollar sign ($)

5. Must start with a letter, _, or $

 Not Allowed

1. Cannot start with a digit

2. Cannot contain spaces

3. Cannot use special characters (@, #, %, etc.)

4. Cannot use Java keywords

 3. Java Keywords (Cannot Be Identifier)

Examples:

•  These words are reserved by Java.

 4. Case Sensitivity in Identifiers

Java is case-sensitive:

• age and Age are different identifiers

 5. Naming Conventions (Best Practice)

Variables & Methods → camelCase

Classes → PascalCase

Constants → UPPER_CASE

 6. Valid vs Invalid Identifiers (Quick Table)

 7. Meaningful Identifiers (Recommended)

 Bad:

Good:

 8. Interview Questions (Must Know)

Q1: Can an identifier start with $?
 Yes

Q2: Can Java keywords be identifier?
 No

Q3: Is Java case-sensitive?
Yes

Q4: Is _ allowed as an identifier?
 Yes (but avoid alone _ in modern Java)

 Quick Cheat Sheet