Java Basics: Variables & Data Types

AP Computer Science A (CSA) is taught in Java. Everything starts with declaring variables and choosing the right data type.

Primitive types

• int — whole numbers (e.g. 42)
• double — decimals (e.g. 3.14)
• boolean — true or false
• char — a single character (e.g. 'A')

String is not a primitive — it is an object that stores text: String name = "Uğur";

Declaring and assigning

int age = 17;
double gpa = 3.85;
boolean passed = true;

Integer division & casting

Dividing two int values truncates (drops the decimal):

int a = 7 / 2;        // 3, not 3.5
double b = 7.0 / 2;   // 3.5
double c = (double) 7 / 2; // 3.5 — cast first

Worked example

What is the value of 9 / 4 and 9 % 4 in Java?

9 / 4 is 2 (integer division); 9 % 4 is 1 (the remainder).

Exam tip

The most common multiple-choice trap is integer division: 5 / 2 is 2, not 2.5. To get a decimal result, at least one operand must be a double (or use a cast). Also remember char is compared/stored by its numeric code, and String values are compared with .equals(), not ==.