Variable is name of reserved area allocated in memory. In other words, it is a name of memory location. It is a combination of “vary + able” that means its value can be changed.
Variable in Java is a data container that stores the data values during Java program execution. Every variable is assigned data type which designates the type and quantity of value it can hold. Variable is a memory location name of the data. The Java variables have mainly three types : Local, Instance and Static.
To declare a variable, you must specify the data type & give the variable a unique name.
Examples of other Valid Declarations are
int a,b,c; float pi; double d; char a;
To initialize a variable, you must assign it a valid value.
Example of other Valid Initializations are
pi =3.14f; do =20.22d; a=’v’;
The Java programming language defines the following kinds of variables:
- Instance Variables (Non-Static Fields) Technically speaking, objects store their individual states in “non-static fields”, that is, fields declared without the
statickeyword. Non-static fields are also known as instance variables because their values are unique to each instance of a class (to each object, in other words); the
currentSpeedof one bicycle is independent from the
- Class Variables (Static Fields) A class variable is any field declared with the
staticmodifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated. A field defining the number of gears for a particular kind of bicycle could be marked as
staticsince conceptually the same number of gears will apply to all instances. The code
static int numGears = 6;would create such a static field. Additionally, the keyword
finalcould be added to indicate that the number of gears will never change.
- Local Variables Similar to how an object stores its state in fields, a method will often store its temporary state in local variables. The syntax for declaring a local variable is similar to declaring a field (for example,
int count = 0;). There is no special keyword designating a variable as local; that determination comes entirely from the location in which the variable is declared — which is between the opening and closing braces of a method. As such, local variables are only visible to the methods in which they are declared; they are not accessible from the rest of the class.
- Parameters You’ve already seen examples of parameters, both in the
Bicycleclass and in the
mainmethod of the “Hello World!” application. Recall that the signature for the
public static void main(String args). Here, the
argsvariable is the parameter to this method. The important thing to remember is that parameters are always classified as “variables” not “fields”. This applies to other parameter-accepting constructs as well (such as constructors and exception handlers) that you’ll learn about later in the tutorial.