Identifiers and Keywords

Identifiers are used to name Java language entities. They begin with a Unicode letter, underscore character (_), or dollar sign ($). Subsequent characters consist of these characters and the digits 0–9. Identifiers are case sensitive and cannot be the same as a reserved word or the boolean values True or False or the null value. Avoid using the dollar sign character; it is intended for use by compiler-generated identifiers.

The following are examples of valid Java identifiers:

  • Identifier

  • $my_identifier

  • $123

The following are invalid Java identifiers:

  • 1badIdentifier

  • bad-too

  • %badID

The following words are reserved by the Java language and cannot be used as identifiers:

abstractdoimportreturntry
booleandoubleinstanceofshort

Get Sun Certification Training Guide (310-025, 310-027): Java™ 2 Programmer and Developer Exams now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.

Start your free trial