What is the Variable?How many type of variables are in Java?

Variables in Java

A variable is a name given to a memory location. It is the basic unit of storage in a program.

• The value stored in a variable can be changed during program execution.
• A variable is only a name given to a memory location, all the operations done on the variable effects that memory location.
• In Java, all the variables must be declared before use.

Declare variables

We can declare variables in java as follows:

datatype: Type of data that can be stored in this variable.

variable_name: Name given to the variable.

value: It is the initial value stored in the variable.

Types of variables

There are three types of variables in Java:

• Local Variables
• Instance Variables
• Static Variables

Local Variables: A variable defined within a block or method or constructor is called local variable.

• These variable are created when the block in entered or the function is called and destroyed after exiting from the block or when the call returns from the function.
• The scope of these variables exists only within the block in which the variable is declared. i.e. we can access these variable only within that block.
• Initialization of Local Variable is Mandatory.

Sample Program 1:

Output:

Student age is : 5

In the above program, the variable age is a local variable to the function StudentAge(). If we use the variable age outside StudentAge() function, the compiler will produce an error as shown in below program.

Sample Program 2:

Output:

Compilation Error in java code :- 
prog.java:12: error: cannot find symbol
        System.out.println("Student age is : " + age);
                                                 ^
  symbol:   variable age
  location: class StudentDetails
1 error

Instance Variables: Instance variables are non-static variables and are declared in a class outside any method, constructor or block.

• As instance variables are declared in a class, these variables are created when an object of the class is created and destroyed when the object is destroyed.
• Unlike local variables, we may use access specifiers for instance variables. If we do not specify any access specifier then the default access specifier will be used.
• Initialization of Instance Variable is not Mandatory. Its default value is 0
• Instance Variable can be accessed only by creating objects.

Sample Program:

Output:

Marks for first object:
50
80
90
Marks for second object:
80
60
85

As you can see in the above program the variables, engMarks , mathsMarks , phyMarksare instance variables. In case we have multiple objects as in the above program, each object will have its own copies of instance variables. It is clear from the above output that each object will have its own copy of instance variable.

Static Variables: Static variables are also known as Class variables.

• These variables are declared similarly as instance variables, the difference is that static variables are declared using the static keyword within a class outside any method constructor or block.
• Unlike instance variables, we can only have one copy of a static variable per class irrespective of how many objects we create.
• Static variables are created at the start of program execution and destroyed automatically when execution ends.
• Initialization of Static Variable is not Mandatory. Its default value is 0
• If we access the static variable like Instance variable (through an object), the compiler will show the warning message and it won’t halt the program. The compiler will replace the object name to class name automatically.
• If we access the static variable without the class name, Compiler will automatically append the class name.

To access static variables, we need not create an object of that class, we can simply access the variable as

class_name.variable_name;

Sample Program:

Output:

Harsh's average salary:1000.0