VARIABLES

A variable is a basic unit of storage, which represents memory location in which value can be

stored.

Rules for variables:

1. They must not begin with a digit

2. It should not be a keyword

3. White space is not allowed

4. Variable names can be of any length

DECLARATION OF VARIABLES

Before using any variable, it must first be declared. A variable declaration specifies the

datatype, the variable name, and optionally the default value for the variable.

Syntax: datatype identifier {=default value}

Ex: byte b;

int age, enrolno

boolean male

GIVING VALUES TO VARIABLES

Once you have declared the type of a variable, you can initialize it with some value.

Syntax: variable name=some value

Ex: int year=20;

SCOPE OF VARIABLES

Java actually has three kinds of variables

Instance variables

Class variables

Local variables

Instance variables are created when the objects are instantiated and therefore they are

associated with the objects. They take different values for each object. Class variables are

similar to instance variables, except their values apply to all the instances of a class rather

than having different values for each object. Local variables are declared and used inside

methods.

Variables :

Variables are also the key to creating programs that can perform calculations.

Type of Variables :

1. class variable

2. Instance variable

3. Local variable

4. Final variable

5. shadowing variable

Class Variable :

A class variable is a variable that any method in a class can access, including static

methods such as main.

When declaring a class variable you have two basic rules to follow:

1. You must place the declarations within the body of the class, but not within any of

the class method.

2. You must include the word static in the declaration. The word static comes before the

variable type.

E.g.: public class helloapp {

static string hellomessage;

public static void main(String[] args) {

hellomessage = “Helloworld!”;

System.out.println(“hellomessage”);

}

}

Instance variable :

An instance variable is similar to a class variable, but doesn’t specify The word static in its

declaration.

• Instance variables are associated with instances of classes.

E.g.:

public class helloapp {

string hellomessage;

public static void main(String[] args) {

hellomessage = “Helloworld!”;

System.out.println(“hellomessage”);

}

}

Error :

Cannot make a static reference to the non-static field hellomessage

Local variable :

A local variable is a variable that’s declared within the body of a method.

• You don’t specify “static” on a declaration for a local variable.

• local variables are not given initial default values. The compiler checks to make sure

that you have assigned a value before you use a local variable.

Final variable (Constants) :

• A final variable, also called a constant.

• It is a variable whose value you can’t change once it’s been initialized.

Final variables are class or instance variables

Shadowing variables :

A shadowing variable is a variable that would otherwise be accessible, but is temporarily

made unavailable because a variable with the same name has been declared in a more

immediate scope.

Scope :

The scope of a variable refers to which parts of a class the variable exists in.

*SYMBOLIC CONSTANTS

symbolic constants are used like macros in C and C++

symbolic names take the same form as variable names. But, they are written in capitals to

visually distinguish them from normal variables. After declaration of symbolic constants they

should not be assigned to any other within the program by using an assignment statement.

A constant can be declared as follows:

Examples:

final int STRENGTH = 100;

final int PASS_MARK = 50;

final float PI = 3.14159;