Data Types, Variables, and Operators

Java primitives are boolean, byte, short, int, long, char, float, and double. Reference variables point to objects or hold null. Fields receive default values; local variables must be definitely assigned before reading. Prefer the smallest domain-appropriate type, not merely the smallest storage width.

Values and expressions

final int secondsPerHour = 60 * 60;
long population = 1_428_000_000L;
double ratio = 5.0 / 8.0;
char grade = 'A';
String label = "Java";
boolean valid = population > 0 && label != null;

Arithmetic includes + - * / %; integer division truncates. Relational operators yield booleans. && and || short-circuit, while & | ^ ~ << >> >>> also operate on bits. Numeric promotion may widen operands; narrowing needs an explicit cast and can lose data. Integer overflow wraps in two’s-complement arithmetic, so use Math.addExact when overflow is an error. == compares primitive values but reference identity; object value equality normally uses equals.