Java Basics (Data Types, Variables, Literals)

Data Types

Describe possible operations on the data and the storage method. In Java, they are classified into primitive (standard) and abstract (derived) data types.

Primitive Data Types

Built into the Java language, not objects, and have no methods. Includes byte, short, int, long, float, double, char, boolean.

Byte

Smallest integer type, stores values from -128 to 127, size 8-bit.

Short

Integer type, range -32,768 to 32,767, size 16-bit.

Int

Most commonly used integer type, range -2,147,483,648 to 2,147,483,647, size 32-bit.

Long

Large integer type, suffix L must be added, size 64-bit.

Float

Single precision floating-point, used for fractional numbers, suffix f required, size 32-bit.

Double

Double precision floating-point, default for decimals in Java, size 64-bit.

Char

Stores a single character (Unicode), size 16-bit, range 0 to 65,535.

Boolean

Logical type with only true or false values, size 1-bit.

Abstract Data Types

Based on primitive types but with more functionality. Example: String, used to store characters, symbols, and words.

Variable

A named memory location that stores data, which can change during program execution.

Constant

Similar to variables but values cannot be changed once assigned.

Variable Naming Rules

Must be meaningful, unique, start with a letter, dollar sign, or underscore, cannot use keywords, and avoid symbols/spaces.

Variable Naming Conventions

Use meaningful names, start with lowercase, use camelCase for multi-word names (e.g., empGender).

Default Values of Variables

Primitive types have defaults (e.g., int = 0, float = 0.0, boolean = false, char = '\u0000'). Objects (like Strings) default to null.

Literals

Constant values directly assigned to variables.

Boolean Literals

Types of Literals

true, false

Integer Literals

Types of Literals

Decimal, octal (0 prefix), hexadecimal (0x prefix), binary (0b prefix)

Floating-point Literals

Types of Literals

Numbers with decimal, require F/f suffix for floats

Character Literals

Types of Literals

Single characters in ' ', can use Unicode or escape sequences ('\n', '\t')

String Literals

Types of Literals

Sequence of characters in " "