In Java, tokens are the smallest units of code that have meaning in the language. They are the building blocks of Java programs and can be categorized into several types:

1. Keywords

Keywords are reserved words in Java that have special meanings in the language. They cannot be used as identifiers (names for variables, methods, classes, etc.). Examples include:

• class, public, static, void, int, if, else, while, for, return, try, catch, finally

2. Identifiers

Identifiers are names given to variables, methods, classes, and other elements. They must start with a letter, underscore (_), or dollar sign ($), and can be followed by letters, digits, underscores, or dollar signs. Examples:

• myVariable, calculateSum, Person, $_tempValue

3. Literals

Literals are constant values directly written in the code. They represent fixed values for various data types:

• Integer Literals: 42, 0xFF, 075
• Floating-Point Literals: 3.14, 2.71e-2
• Character Literals: 'a', '1', '\n'
• String Literals: "Hello, World!", "Java"
• Boolean Literals: true, false
• Null Literal: null

4. Operators

Operators perform operations on variables and values. They can be categorized into:

• Arithmetic Operators: +, -, *, /, %
• Relational Operators: ==, !=, >, <, >=, <=
• Logical Operators: &&, ||, !
• Assignment Operators: =, +=, -=, *=, /=, %=
• Unary Operators: +, -, ++, --, !
• Bitwise Operators: &, |, ^, ~, <<, >>, >>>
• Conditional (Ternary) Operator: ? :
• Instanceof Operator: instanceof

5. Separators (Delimiters)

Separators are used to define the structure of the code:

• Semicolon (;): Ends a statement.
• Comma (, ): Separates items in lists.
• Dot (.): Accesses members of a class or object.
• Parentheses (()) and Braces ({}): Used for grouping and defining blocks of code.
• Brackets ([]): Used for array indexing.

6. Comments

Comments are used to annotate code and are ignored by the compiler. They can be:

• Single-Line Comments: // This is a comment
• Multi-Line Comments: /* This is a multi-line comment */
• Javadoc Comments: /** This is a Javadoc comment */

Summary

• Keywords: Reserved words with special meanings (e.g., class, public).
• Identifiers: Names for variables, methods, classes, etc. (e.g., myVariable, calculateSum).
• Literals: Constant values (e.g., 42, "Hello").
• Operators: Symbols that perform operations (e.g., +, -, *).
• Separators: Symbols used to define code structure (e.g., ;, {}, []).
• Comments: Annotations in the code (e.g., //, /* */).

Understanding these tokens is fundamental for writing and understanding Java code, as they form the basic syntax and structure of the language.