Java Identifiers

Identifiers

All Java variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

Note: It is recommended to use descriptive names in order to create understandable and maintainable code:

// Good
int minutesPerHour = 60;

// OK, but not so easy to understand what m actually is
int m = 60;

The general rules for naming variables are:

• Names can contain letters, digits, underscores, and dollar signs
• Names must begin with a letter
• Names should start with a lowercase letter, and cannot contain whitespace
• Names can also begin with $ and _
• Names are case-sensitive ("myVar" and "myvar" are different variables)
• Reserved words (like Java keywords, such as int or boolean) cannot be used as names

Invalid Identifiers

Here are some examples of invalid identifiers that would cause errors:

// Invalid identifiers:
int 2ndNumber = 5;  // Cannot start with a digit
int my var = 10;    // Cannot contain spaces
int int = 20;       // Cannot use reserved keywords