CODEWITHSUNDEEP
javavariablesscope
Dhairya Patel
Dhairya Patel

Reputation: 49

Java8 variables scope

I took mock exam test as i am preparing for OCAJP exam and i came across this below question on Variables and Scope of Variables. 

public class HelloWorld{
     static int x = 2;            
     public static void main(String []args){
        if(x>1)
        {
            x++;
            int x = 4;
        }
        System.out.println(x);
        final int x = 10;
     }
}

and the output for the above code is "3". But i am unable to figure out why the output is 3. I can understand that the "int x=4" within the if block will be seen outside the IF block. But should not "final int x = 10;" throw compiler off-track as there is already x as a static variable?

Upvotes: 4

Views: 85

Answers (1)

rgettman
rgettman

Reputation: 178263

Let's take this in code order.

static int x = 2;

This declares a static class variable named x that is initialized to 2.

if(x>1)

This refers to the static class variable, because the other declarations of x haven't occurred yet.

    x++;

This increments the static class variable x to 3.

    int x = 4;

This declares a new local variable x, distinct from the static class variable x, and initializes it to 4. This new local variable shadows the static class variable. However, it immediately goes out of scope; its scope is limited to the if block. It is not referenced after declaration and before it goes out of scope.

System.out.println(x);

This prints the only x in scope, the static class variable, which is 3. The local x declared above is out of scope and no longer shadows the static class variable.

final int x = 10;

This declare another new local variable x, also distinct from the static class variable x and distinct from the already out of scope x previously declared in the if block, and initializes it to 10. This new local variable shadows the static class variable. However, it also immediately goes out of scope; its scope is limited to the main method block. It is also not referenced after declaration and before it goes out of scope.

The main points are:

  • A local variable can shadow a class variable of the same name. However, it only does so in its own local scope.
  • Variables not yet declared do not shadow the class variable yet.

Upvotes: 5

Related Questions