In Java, tokens are the smallest units of a program that have a meaning. They are the building blocks of the Java programming language. When you write Java code, the compiler breaks it down into these tokens for further analysis and processing. The main types of tokens in Java are:

Keywords: These are reserved words that have a predefined meaning in the language and cannot be used for any other purpose. Examples include class, public, static, void, int, if, else, for, and while.

Identifiers: These are names given to various program elements such as classes, methods, variables, and objects. Identifiers must start with a letter, underscore (_), or dollar sign ($), followed by letters, digits, underscores, or dollar signs. For example, main, sumTotal, and StudentName are identifiers.

Literals: These represent fixed values that appear directly in the code. Examples include numeric literals (10, 3.14), character literals (‘a’, ‘1’), and string literals (“Hello World”).

Operators: These are symbols that perform operations on variables and values. Examples include + (addition), – (subtraction), * (multiplication), / (division), = (assignment), == (equality), and && (logical AND).

Punctuation: These symbols help structure the code and separate different parts of the program. Examples include semicolons (;), commas (,), parentheses (()), curly braces ({}), and periods (.).

Each of these tokens plays a specific role in the syntax and structure of Java programs. Understanding how they work is fundamental to writing correct and efficient Java code.