Variables and data types

1 Learn

A variable is a named box that stores a value. Before using a variable, you say what type of value it holds.

Common types: int (whole numbers), double (decimal numbers), char (one character in single quotes), boolean (true or false) and String (text in double quotes).

The name of a variable is an identifier. It can use letters, digits, _ and $, but cannot start with a digit or be a keyword like class.

Want more detail? Open the full lesson

2 See the Code

Java

public class Student {
    public static void main(String[] args) {
        String name = "Ananya";
        int age = 19;
        double marks = 86.5;
        char grade = 'A';
        boolean passed = true;

        System.out.println(name + " is " + age);
        System.out.println("Marks: " + marks + ", Grade: " + grade);
        System.out.println("Passed: " + passed);
    }
}

Each line creates a variable with a type, a name and a value.
The + sign joins text and values together when printing.
char uses single quotes 'A'; String uses double quotes "Ananya".

Output

Ananya is 19
Marks: 86.5, Grade: A
Passed: true

3 Practice

Create variables for a book: title (String), pages (int), price (double) and available (boolean). Print them.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. Which type stores 3.75?
2. Which is a valid variable name?
3. What type is 'Y'?

Step 5

Answer and check the Quick Check above to unlock this.

Day 1