Java Identifiers

As the name suggests, Java identifiers are used to essentially identify the code and break it down to several parts. This greatly enhances the readability of the code. A Java identifier can be anything starting from class names to variables names or any such labels that demarcate segments of code.

Let’s take the example of a simple code below:

public class Demo
{
public static void main (String args [])
{
double db = 20.0;
}
}

The above code has the following identifiers:

• Demo: Name of the class.
• main: Name of the method.
• String: Library Class name.
• args: Name of a variable of String type.
• db: Name of the double variable we have chosen.

Rules for Defining Java Identifiers

Java has defined some rules when naming identifiers. Violating these rules result in compilation errors:

• Only alphanumeric characters are allowed when naming an identifier. ( [A – Z], [a – z], [0 – 9]), ‘$’ (dollar sign) and ‘_’ (underscore). Any other special character will not be accepted when compiling your code.
• The sequence of identifiers is such that it should always start with a character. It can then be followed by digits but never vice versa.
• Java identifiers are case-sensitive.
• Although identifiers can be as long as you want, an optimal length is anything between 4 to 15 letters.
• Reserved words cannot be used as identifiers.

Examples of Valid Identifiers:

TestA
TESTA
testa
x
x1
_testA
$testA

Examples of Invalid Identifiers:

Test A //Cannot contains space
123A //Should not start with letters
x+y //’+’ is not acceptable.

Reserved Words

Reserved Words are those words that have special meaning in the gambit of the programming language of Java. Reserved words are formed of 50 keywords and 3 literals. These words cannot be used as identifiers.