Why doesn't Java allow creating integers inside a conditional statement

Question

When I try the below code, it gives me an error

int a =1,b=2;
if(a < b)
 int c = 10;

But if I do the same adding curly braces, it works fine

int a =1,b=2;
if(a < b)
{
 int c = 10;
}

But I'm just curious as to why Java does not allow creating a variable inside an if-condition.

Answer 1

It's nothing about integers, it's just that you cannot have a declaration under an if statement without brackets. Note that it would be totally pointless since it would mean the declaration would be local to the if statement, which would also have a single instruction (it's the meaning of no brackets), which means this declaration would never be used.

To make it more "visual":

if (condition) instruction;

is equivalent to

if (condition) {
    instruction;
}

so in your case

if(a < b) {
   int c = 10;
}

is a pointless code since c will never be used. Therefore, it makes no sense for Java to allow writing

if(a < b) int c = 10;

An if statement with brackets will allow you any content in the block (even no content at all) but if you make a declaration withoutusing the declared variable you'll still get a warning.

Answer 2

Your int c = 10; is supposed to be a block local variable. You can only have these inside, well, a block (or some control structures like for ), and these blocks are denoted by curlies. A naked int c = 10; is not a block.