Variables In Java

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:

Syntax

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 “skillsforyou”:

public class MyClass

{
public static void main(String[] args)

{
String name = “skillsforyou”;
System.out.println(name);
}
}

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

public class MyClass

{
public static void main(String[] args)

{
int myNum = 12;
System.out.println(myNum);
}
}

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

public class MyClass

{
public static void main(String[] args)

{
int myNum;
myNum = 18;
System.out.println(myNum);
}
}

A demonstration of how to declare variables of other types:

Example

int myNum = 4;
float myFloatNum = 4.66f;
char myLetter = ‘A’;
boolean myBool = true;
String myText = “Hello”;

Display Variables

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

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

public class MyClass

{
public static void main(String[] args)

{
String name = “Ruchika”;
System.out.println(“Hello ” + name);
}
}

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

public class MyClass

{
public static void main(String[] args)

{
String firstName = “Ruchika “;
String lastName = “Katoch”;
String fullName = firstName + lastName;
System.out.println(fullName);
}
}

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

public class MyClass

{
public static void main(String[] args)

{
int x = 8;
int y = 2;
System.out.println(x + y); // Print the value of x + y
}
}

From the example above, you can expect:

• x stores the value 8
• y stores the value 2
• Then we use the println() method to display the value of x + y, which is 10
• Declare Many VariablesTo declare more than one variable of the same type, use a comma-separated list:

public class MyClass

{
public static void main(String[] args)

{
int x = 2, y = 8, z = 20;
System.out.println(x + y + z);
}
}

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