Expressions and Operators

Java Fundamentals: Data Types, Variables, and Operators

By the end of this lesson, you will be able to declare and initialize variables of primitive types, use operators in expressions, and understand Java's type system.

Java Overview

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Java is a statically typed, object-oriented, compiled programming language. Every variable must have a type declared before use; the compiler checks types at compile time.

Program structure:

• Every Java program lives in a class
• Execution starts in the main method
• Statements end with a semicolon ;
• Java is case-sensitive: myVar ≠ MyVar

Primitive Data Types

Java has 8 primitive types. The AP exam focuses on three:

Type	Description	Example
int	32-bit integer	int count = 42;
double	64-bit floating-point	double pi = 3.14;
boolean	true or false	boolean done = false;

Also used (not heavily tested):

• char: single character in single quotes: char grade = 'A';
• String: technically a class, not a primitive, but used like one

Declaration and initialization:

int x;          // declaration only
x = 10;         // assignment
int y = 5;      // declaration + initialization (preferred)

Integer division: when both operands are int, division truncates (does not round).

int result = 7 / 2;  // result is 3, NOT 3.5