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Rules for Naming Identifiers

The rules for naming an identifier are:
An identifier can consist of letters, digits 0–9, underscore ( _ ), and dollar ($) symbol.

An identifier cannot start with a digit.
Keywords cannot be used as an identifier.
No special symbols like !, @, #, %, etc. can be used in an identifier.

Identifiers are case-sensitive, which means ‘name’ and ‘NAME’ are two different identifiers.
Examples of some valid identifier names are Employee123, mygood_book, _address93, FirstName,
age, etc.

Examples of some invalid identifier names are 1_Name, @Address, 1234, –Age, etc.
Keywords

Keywords are the reserved words that cannot be used as identifier names as they carry a special
meaning for the Java compiler. Some of the Java keywords are given below:
Java Keywords
abstract class final interface static

assert const float long switch
boolean continue for new this
break default if private throw
byte do implements protected throws
case double import public try

catch else instanceof return void
char extends int short while

Although reserved as a keyword in Java, const is not used and has no function.

There are three more reserved words in Java: true, false, and null. Technically, they are literal values
and not keywords. However, they cannot be used as identifiers, and they have a specific meaning to
the Java compiler.

Data Types

A data type is used to define the size and type of value that a variable can store. The Java language is
rich in its data types. Java provides two types of data types: primitive and non-primitive.

Primitive Data Types

Java provides eight basic data types, which are as given in the following table:

Data Type Size (in bits) Minimum Value Maximum Value
byte 8 –128 127
short 16 –32768 32767
int 32 –2147483648 2147483647

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