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(Decimal) 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.It either stores true or it stores false.It cant store both at a time.

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 orname). The equal sign is used to assign values to the variable.

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

Example

Create a variable called car of type String and assign it the value “Benz“: Ans: String car= “Benz”;
System.out.println(name);

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

Example

Create a variable called myAgeof type int and assign it the value 15:
Ans: int myAge = 15;
System.out.println(myNum);

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

Example

int myAge;
myAge= 15;
System.out.println(myNum);

A demonstration of how to declare variables of other types:

Example

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:

Example

String name = “John”;
System.out.println(“Hello ” + name);

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

Example

String firstName = “Salifu”;
String lastName = “Jibril”;
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):

Example

int a = 9;
int b = 4;
System.out.println(a + b); // Print the value of a + b

From the example above, you can expect:

  • a stores the value 9
  • b stores the value 4
  • Then we use the println() method to display the value of a + b, which is 13

Declare Many Variables

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

Example

int x = 6, y = 9, z = 50;
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

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