CODEWITHSUNDEEP
javavariablesscopesyntax-error
Jigyanshu Shrivasytava
Jigyanshu Shrivasytava

Reputation: 39

declaration of variable inside a loop vs multiple declarations of the same variable name

the following code gives an error, because the variable m was defined twice.

class one {
   public static void main(String args[]) {
     int m=10;
     int m=10;
   }
 }

but when the declaration is done inside a loop, it is OK, even though m is still being defined twice.

 class one {
   public static void main(String args[]) {
     for(int i=1;i<=2;i++) {
       int m=10;
     }
   }
 }

and the compiler does not give back an error message.
can you explain the differences between the two, and how come sometimes i can declare the same variable twice inside the same method, and sometimes not?

Upvotes: 2

Views: 3982

Answers (6)

Episodex
Episodex

Reputation: 4559

In simple words, you are not declaring this variable twice in second example. As variable lifespan ends on the closing } of the block in which it was declared, by the time you declare m in second iteration, first one is "dead". This is why you can do it in a loop.

In first example you declare two variables with the same name in the same code block, which are supposed to "live" simultaneously. This is forbidden as you can't tell which variable you refer too by writing m.

Upvotes: 0

Kumar Vivek Mitra
Kumar Vivek Mitra

Reputation: 33534

- In the First code you have declared m twice in the same scope, and it continues till the main() method ends.

- Where as within the loop everytime a primitive int variable m is created with a value, so its obviously not a problem.

Upvotes: 0

gilad hoch
gilad hoch

Reputation: 2866

you get the error is because you defined the same variable twice in the same block (scope). when you run inside a loop, you "open" a new scope for every iteration of the loop, so you can define a variable that is visible only within this scope (won't be accible outside the loop though). for instance, if you had written something like that:

class one {    
    public static void main(String args[]) {     
        {
            int m=10;
        }
        {
            int m=10;
        }
    }
}

it would have been compiled just fine, because the variables of the same name, does not share the same scope.

Upvotes: 0

VoidWhisperer
VoidWhisperer

Reputation: 73

It's creating an error in the first one because you are declaring the varible twice.

Upvotes: 0

Anand
Anand

Reputation: 21320

You cannot declare a variable with the same name more than once in a block of code.

In first case, you are declaring the same variable in a block of code i.e. main. In second case, after the first iteration of for loop, variable m is destroyed and recreated over the second iteration

Upvotes: 0

Abubakkar
Abubakkar

Reputation: 15664

For the first case m is referenced till the end of the main method so you can't have two variable of the same name in the same scope.

Whereas in the second case, for every time the loop executes, m for the last iteration is no longer referenced and hence you are able to redeclare and reinitialize it.

Upvotes: 2

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