Java Variables

Java Variables

Variables are containers for storing data values.

In Java, there are different types of variables, for example:

  • String - stores text, such as "Hello". String values are surrounded by double quotes
  • int - stores integers (whole numbers), without decimals, such as 123 or -123
  • float - stores floating point numbers, with decimals, such as 19.99 or -19.99
  • char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
  • boolean - stores values with two states: true or false

Declaring (Creating) Variables

To create a variable, you must specify the type and assign it a value:


type variable = value;

Where type is one of Java's types (such as int or String), and variable is the name of the variable (such as x or name). The equal sign is used to assign values to the variable.

To create a variable that should store text, look at the following example:


Create a variable called name of type String and assign it the value "John":

String name = "John";
Run example »

To create a variable that should store a number, look at the following example:


Create a variable called myNum of type int and assign it the value 15:

int myNum = 15;
Run example »

You can also declare a variable without assigning the value, and assign the value later:


int myNum;
myNum = 15;
Run example »

A demonstration of how to declare variables of other types:


int myNum = 5;
float myFloatNum = 5.99f;
char myLetter = 'D';
boolean myBool = true;
String myText = "Hello";

You will learn more about data types in the next chapter.

Display Variables

The println() method is often used to display variables.

To combine both text and a variable, use the + character:


String name = "John";
System.out.println("Hello " + name);
Run example »

You can also use the + character to add a variable to another variable:


String firstName = "John ";
String lastName = "Doe";
String fullName = firstName + lastName;
Run example »

For numeric values, the + character works as a mathematical operator (notice that we use int (integer) variables here):


int x = 5;
int y = 6;
System.out.println(x + y); // Print the value of x + y
Run example »

From the example above, you can expect:

  • x stores the value 5
  • y stores the value 6
  • Then we use the println() method to display the value of x + y, which is 11

Declare Many Variables

To declare more than one variable of the same type, use a comma-separated list:


int x = 5, y = 6, z = 50;
System.out.println(x + y + z);
Run example »

Java Identifiers

All Java variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

The general rules for constructing names for variables (unique identifiers) are:

  • Names can contain letters, digits, underscores, and dollar signs
  • Names should begin with a letter
  • Names can also begin with $ and _ (but we will not use it in this tutorial)
  • Names are case sensitive ("myVar" and "myvar" are different variables)
  • Names should start with a lowercase letter and it cannot contain whitespace
  • Reserved words (like Java keywords, such as int or String) cannot be used as names

Test Yourself With Exercises


Create a variable named carName and assign the value Volvo to it.

  = ;

Start the Exercise