In Java, data types specify the kind of data that variables can hold. They are broadly categorized into two groups: 1. Primitive Data Types These are the most basic data types built into the language: byte: 8-bit signed integer ranging from -128 to 127. short: 16-bit signed integer ranging from -32,768 to 32,767. int: 32-bit signed integer ranging from -2,147,483,648 to 2,147,483,647. long: 64-bit signed integer ranging from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. float: Single-precision 32-bit IEEE 754 floating point. double: Double-precision 64-bit IEEE 754 floating point. boolean: Represents two possible values: `true` or `false`. char: 16-bit Unicode character. These primitive types are stored directly in memory and are not objects. 2. Reference Data Types These refer to objects and arrays. Unlike primitive types, reference types store references (or addresses) to the actual data. Examples include instances of classes, arrays, and interfaces. For instance, a variable of type `String` holds a reference to a `String` object. Understanding these data types is fundamental to effective Java programming, as they determine the operations that can be performed on the data and how the data is stored in memory.