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:
Where type is one of Java's types (such as
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":
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:
You can also declare a variable without assigning the value, and assign the value later:
myNum = 15;
A demonstration of how to declare variables of other types:
float myFloatNum = 5.99f;
char myLetter = 'D';
boolean myBool = true;
String myText = "Hello";
You will learn more about data types in the next chapter.
println() method is often used to display variables.
To combine both text and a variable, use the
System.out.println("Hello " + name);
You can also use the
+ character to add a variable to another variable:
String lastName = "Doe";
String fullName = firstName + lastName;
For numeric values, the
+ character works as a mathematical operator (notice that we use
int (integer) variables here):
int y = 6;
System.out.println(x + y); // Print the value of x + y
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:
System.out.println(x + y + z);
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
String) cannot be used as names