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This chapter is from the book

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.

Know Your Java-Reserved Words

It is a good idea to memorize this list because you are likely to seeat least one exam-related question that requires knowledge of the preceding keywords. Also, remember that null, true, and false are literal values and not reserved keywords.

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:

abstract do import return try
boolean double instanceof short void
break else int static volatile
byte extends interface strictfp while
case final long super


catch finally native switch


char float new synchronized


class for package this


const goto private throw


continue if protected throws


default implements public transient


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