Scope of Variables in Java

In programming, scope of variable defines how a specific variable is accessible within the program or across classes. In this section, we will discuss the scope of variables in Java.

Scope of a Variable

In programming, a variable can be declared and defined inside a class, method, or block. It defines the scope of the variable i.e. the visibility or accessibility of a variable. Variable declared inside a block or method are not visible to outside. If we try to do so, we will get a compilation error. Note that the scope of a variable can be nested.

• We can declare variables anywhere in the program but it has limited scope.
• A variable can be a parameter of a method or constructor.
• A variable can be defined and declared inside the body of a method and constructor.
• It can also be defined inside blocks and loops.
• Variable declared inside main() function cannot be accessed outside the main() function

Demo.java

In Java, there are three types of variables based on their scope:

1. Member Variables (Class Level Scope)
2. Local Variables (Method Level Scope)

Member Variables (Class Level Scope)

These are the variables that are declared inside the class but outside any function have class-level scope. We can access these variables anywhere inside the class. Note that the access specifier of a member variable does not affect the scope within the class. Java allows us to access member variables outside the class with the following rules:

Syntax:

Let's see an example.

VariableScopeExample1.java

Output:

We see that y=100 is unknown. If you want to compile and run the above program remove or comment the statement y=100. After removing the statement, the above program runs successfully and shows the following output.

Sum of x+y = 30

There is another variable named an instance variable. These are declared inside a class but outside any method, constructor, or block. When an instance variable is declared using the keyword static is known as a static variable. Their scope is class level but visible to the method, constructor, or block that is defined inside the class.

Let's see an example.

Product.java

Output:

Product Name: Mac Book
Product Price: 65000.0

Let's see another example.

StaticVariableScope.java

Output:

The value of PI is: 3.14159265359

Local Variables (Method Level Scope)

These are the variables that are declared inside a method, constructor, or block have a method-level or block-level scope and cannot be accessed outside in which it is defined. Variables declared inside a pair of curly braces {} have block-level scope.

Declaring a Variable Inside a Method

Output:

The value of x is: 10

Let's see another example of method-level scope.

DemoClass2.java

Output:

The value of a is: 3

In the above example, we have passed a variable as a parameter. We have used this keyword that differentiates the class variable and local variable.

Declaring a Variable Inside a Constructor

VariableInsideConstructor.java

Output:

Age is: 24

Declaring a Variable Inside a Block

VariableInsideBlock.java

Output:

We see that y=100 is unknown. If you want to compile and run the above program remove or comment the statement y=100. After removing the statement, the above program runs successfully and shows the following output.

Sum of x+y = 30

Let's see another example.

BlockScopeExample1.java

Output:

When we run the above program, it shows an error at line 9, cannot find symbol because we have tried to print the variable x that is declared inside the loop. To resolve this error, we need to declare the variable x just before the for loop.

BlockScopeExample2.java

Output:

0	1	2	3	4	5	6	7	8	9	10