java-tutorial

2) Java Basics

Goal

Learn the building blocks: variables, types, operators, and basic console output.

The mental model

Java is statically typed: variables have a declared type.
Java is compiled to bytecode and run on the JVM.

Variables and primitive types

Common primitives:

int (32-bit integer)
long (64-bit integer)
double (floating point)
boolean (true/false)
char (single UTF-16 code unit)

Example:

int age = 25;
long population = 8_000_000_000L;
double price = 19.99;
boolean active = true;
char grade = 'A';

`var` (local type inference)

var name = "Sam"; // inferred as String

Use var when it improves readability, not when it hides meaning.

Reference types

String is a reference type (an object)

String city = "Colombo";

Operators (the important ones)

Arithmetic: + - * / %
Comparisons: == != < <= > >=
Boolean logic: && || !

Important:

For objects (like String), use .equals() not ==.

String a = "hi";
String b = new String("hi");
System.out.println(a.equals(b)); // true
System.out.println(a == b);       // usually false

Printing

System.out.println("Hello");
System.out.printf("Age: %d%n", age);

Exercises

Create variables of each primitive type and print them.
Convert Celsius to Fahrenheit: $F = C \times \frac{9}{5} + 32$.
Compare two strings using both == and .equals() and observe the difference.

Table of contents