java-data-types

Every value in a program occupies memory, and the compiler needs to know how much space to allocate and how to interpret the bits. Without a type system, the same 32 bits could represent an integer, a floating-point number, or four characters — leading to errors, portability issues, and unpredictable behavior across platforms.

Java has eight primitive data types: byte, short, int, long, float, double, boolean, and char. Each has a fixed size and range that is platform-independent, guaranteeing the same behavior on any JVM. All other types are reference types (objects and arrays).

When a variable of a primitive type is declared, the JVM allocates exactly the specified number of bytes for it (e.g., 4 bytes for int). Primitives are stored directly on the stack (for local variables) or inline in objects (for fields). They are passed by value — a copy is made. Operations on primitives map directly to CPU instructions, making them faster than objects.

• Fixed sizes across all platforms: int is always 32 bits, long always 64 bits
• Signed integers: byte, short, int, long are all signed (no unsigned primitives until Java 8)
• IEEE 754 floats: float and double follow the IEEE 754 standard
• char is unsigned 16-bit: Represents Unicode code units, not ASCII

• Built from: Java Platform Independence — fixed sizes across platforms are a key part of WORA
• Builds into: Java Wrapper Classes — each primitive has a corresponding wrapper type
• Builds into: Java Variables — every variable has a declared type
• Related: Java Memory Management — primitives vs objects have different memory layouts

• No unsigned primitives for byte, short, int, long until Java 8 introduced unsigned API methods
• char != byte: char is 16-bit Unicode, not a single byte
• Floating-point precision: float has ~7 decimal digits, double has ~15 — rounding errors are common
• Division by zero: Integer types throw ArithmeticException; floating-point returns Infinity or NaN