Primitive Types, Variables, and Expressions

Primitive types on the AP exam

Type	Stores	Example
int	whole numbers	int count = 7;
double	decimal numbers	double price = 4.99;
boolean	true or false	boolean done = false;

A variable must be declared with a type before it is used. A final variable cannot be changed after it is assigned.

Arithmetic

Operators: + - / %, with the usual precedence ( / % before + -).

• Integer division truncates: 7 / 2 is 3, not 3.5.
• If either operand is a double, the result is a double: 7 / 2.0 is 3.5.
• Modulus gives the remainder: 17 % 5 is 2. n % 2 == 0 tests for even numbers.

Casting

• (int) 3.9 is 3 (truncation, not rounding).
• (double) 7 / 2 is 3.5 (the cast applies to 7 first).
• Rounding a positive double: (int) (x + 0.5).

Compound assignment

x += 3; means x = x + 3;. Also -=, *=, /=, %=, and x++, x--.

Integer overflow

An int holds values from Integer.MIN_VALUE to Integer.MAX_VALUE. Going past the limit wraps around.

Tracing example

int a = 10;
int b = 4;
double c = a / b;
a %= 3;
b += a;

a / b is integer division, 2, so c is 2.0. Then a is 1 and b is 5.

Quick summary

• int division truncates; use a double operand or a cast for decimals.
• % gives the remainder.
• (int) truncates toward zero.