Java Tokens

Java tokens are the smallest individual units in a program.

Keywords

Keywords are predefined reserved words in Java. Each keyword has a special meaning and is always written in lowercase.

• class
• while
• for
• interface
• abstract

Identifiers

Identifiers are used to name variables, constants, functions, classes, and arrays. They are usually defined by the user and must be different from reserved keywords.

• The first character must be a letter, underscore, or dollar sign.
• An identifier cannot start with digits, but it may contain digits later.
• Whitespace cannot be included.
• Identifiers are case sensitive.

Valid examples include PhoneNumber, PRICE, radius, a, and a1. Invalid examples include 1sum and Sum 1.

Literals

A literal is a notation that represents a fixed value in source code. Once defined, it cannot be changed.

• Integer
• Floating Point
• Character
• String
• Boolean

Operators

Operators are special symbols used to perform mathematical operations or logical manipulations.

• Arithmetic Operators
• Assignment Operators
• Relational Operators
• Unary Operators
• Logical Operators
• Ternary Operators
• Bitwise Operators
• Shift Operators

Separators

Separators are also known as punctuators in Java.

• ; semicolon
• , comma
• . dot
• { } braces
• [ ] bracket
• ( ) parenthesis

Comments

Comments are used to describe the program. Java supports single-line comments and multi-line comments.

• Single line: // comment
• Multi-line: /* comment */

Constants

Constants are fixed values that do not change during execution.

• Integer constants such as 111 and 1234.
• Floating point constants such as 223.14 and 400.054.
• Character constants such as A, m, and 9.
• String constants such as Welcome and Hello.