Java Variables

A variable in Java is a named place to store a value. Programs use variables to remember information, calculate with it, update it, and print it later.

Every Java variable has a type, a name, and a value. The type tells Java what kind of data the variable can hold, such as a whole number, decimal number, character, or text.

Declaring Variables

To create a variable, write its type followed by its name. This is called declaring a variable. Most beginner programs also give the variable a starting value right away.

public class Main {
    public static void main(String[] args) {
        int apples = 6;
        double price = 0.75;
        char grade = 'A';
        String course = "Java";

        System.out.println("Apples: " + apples);
        System.out.println("Price: $" + price);
        System.out.println("Grade: " + grade);
        System.out.println("Course: " + course);

        apples = 8;
        System.out.println("Updated apples: " + apples);
    }
}

Output:

Apples: 6
Price: $0.75
Grade: A
Course: Java
Updated apples: 8

How It Works

The statement int apples = 6; creates a variable named apples. Its type is int, which stores whole numbers, and its starting value is 6.

The statement double price = 0.75; stores a number with a decimal point. The statement char grade = 'A'; stores one character. A char value uses single quotes.

The statement String course = "Java"; stores text. A String value uses double quotes. Notice that String begins with an uppercase S.

After a variable exists, you can use its name in output. In Java, the + operator can join text with a variable’s value, as in "Apples: " + apples.

Changing a Variable

You can assign a new value to an existing variable with the assignment operator, =. In the example, apples = 8; replaces the old value 6 with the new value 8.

Do not repeat the type when changing a variable that has already been declared. Write apples = 8;, not int apples = 8; in the same block of code.

Declaration and Initialization

Declaration means creating the variable name and type. Initialization means giving the variable its first value.

You can declare and initialize a variable in one statement:

int score = 10;

You can also declare first and assign later:

int score;
score = 10;

Both forms are valid, but initializing a variable right away is often clearer for beginners because the variable starts with a known value.

Common Variable Types

Type	Stores	Example
`int`	Whole numbers	`int age = 21;`
`double`	Decimal numbers	`double total = 19.99;`
`char`	One character	`char letter = 'B';`
`boolean`	`true` or `false`	`boolean passed = true;`
`String`	Text	`String name = "Maya";`

Variable Names

A Java variable name can contain letters, digits, underscores, and dollar signs, but it cannot start with a digit. Variable names are case-sensitive, so score and Score are different names.

Choose names that explain what the value means. Names like itemCount, totalPrice, and studentName are easier to understand than names like x or n when a program grows.

Common Mistakes

Forgetting the semicolon after a declaration or assignment.
Using a variable before declaring it.
Writing a variable name with different capitalization by accident.
Putting text in single quotes instead of double quotes.
Trying to store the wrong kind of value for the variable’s type.

Takeaway: declare a Java variable with a type and a name, initialize it with a useful starting value, and use assignment when the value needs to change.