Java Basics›Core· 30 min read

Variables & Types

A variable is a labelled box that stores a value — and in Java every box has a type.

What you will learn

Create variables of different types
Choose between int, double, boolean and String
Print variables together with text

A variable stores a value

A variable is a named place to keep a value so you can use it later. In Java you must say what type of value it holds. This is called being statically typed — the box knows what shape it is.

Type	Holds	Example value
`int`	A whole number	`25`
`double`	A number with decimals	`19.99`
`boolean`	True or false	`true`
`String`	Text (in double quotes)	`"Asha"`

Declaring variables

You write the type, then a name, then = and the value. Here is a small profile:

Four common variable types

int age = 25;
double price = 19.99;
boolean isStudent = true;
String name = "Asha";

System.out.println(name + " is " + age + " years old.");
System.out.println("Student? " + isStudent);
System.out.println("Price: " + price);

Note: Output: Asha is 25 years old. Student? true Price: 19.99 The + sign joins (concatenates) text and values into one line. When a number meets text with +, Java turns the number into text automatically.

A few rules

String starts with a capital S. The number types (int, double) are lowercase.
Text values go in double quotes "like this". Single quotes are only for one character (char).
Variable names usually start lowercase and use camelCase: firstName, isStudent.
You can change a variable later: age = 26; (no type needed the second time).

Watch out: Types are strict. int age = 19.99; will NOT compile, because 19.99 is not a whole number. Use double for decimals.

Tip: If a value should never change, mark it final: final double PI = 3.14159;. Java then stops you from accidentally changing it later.

Q. Which type best stores a product price like 19.99?

Answer: Prices have decimals, so double is correct. int only holds whole numbers, and a price is a number, not text or true/false.

✍️ Practice

Create variables for a book: a String title, an int number of pages, and a double price. Print them in one sentence.
Make a boolean called isAvailable and print it.

🏠 Homework

Create a small profile of yourself using one variable of each type (int, double, boolean, String) and print a tidy summary.