#2-Known is a drop! JAVA - Datatypes

Source: Dev.to

Data types in JAVA

A datatype in programming defines the type of data a variable can hold, how much memory it occupies, and what operations can be performed on it.

Java is a statically‑typed language because variable types are checked at compile time and must be explicitly declared.

Java has primitive data types and non‑primitive data types.

Variable Nomenclature

Rules

• Must start with a letter, _, or $
• Cannot start with a number
• Cannot use Java keywords
• Case‑sensitive
• No spaces allowed

Conventions (Best Practice)

• Use camelCase → studentAge, totalMarks
• Use meaningful names
• Avoid single‑letter names (except i, j in loops)
• Constants → UPPERCASE (e.g., MAX_SIZE, PI)

Primitive Datatypes

Why Byte Size Matters for Different Data Types

• Range matters because it defines what numbers a variable can safely store.
• Too small → overflow / wrong results
• Too large → wastes memory

Understanding 2’s Complement

Default Values

If a field is declared but not initialized, the compiler assigns a default value (typically 0 for numeric types, false for boolean, and null for reference types). Relying on these defaults is generally considered bad programming style.

Using Underscore Characters in Numeric Literals (Java 7+)

Underscores can appear anywhere between digits to improve readability.

long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 3.14_15F;

long hexBytes = 0xFF_EC_DE_5E; // hexadecimal literal
long hexWords = 0xCAFE_BABE;

byte by = 0b0010_0101; // binary literal, value 37 decimal