Can someone help me understand the scoping rules in Java? This is clearly not valid:
{
int i = 0;
System.out.println(i); // fine, of course
}
System.out.println(i); // syntax error
i is declared within the {}, and it's not available outside. So what about this:
for (int i = 0; i < 10; i++) {
System.out.println(i); // fine, of course
}
System.out.println(i); // syntax error, same as above.
I'm surprised at the syntax error here. i is declared in the outer scope yet it is not available later on. Is it bound to the inner block scope by some special rule for for loops? Are there other scenarios where this can happen?
think of for loop actually represented like this:
{
int i = 0;
while (i < 10) {
// your code
i ++
}
}
Is it bound to the inner block scope by some special rule for for loops?
Yes, this is exactly the case.
There's obviously the local variable declaration:
class Some {
public void x( int i ) {
System.out.println( i ); // valid
}
int j = i; // not valid
}
See also:
- Scope of a Declaration
- Scope of Local Variable Declarations
From the language specification.
It's the defined behavior of the for loop in Java.
class ForDemo {
public static void main(String[] args){
for(int i=1; i<11; i++){
System.out.println("Count is: " + i);
}
}
}
Notice how the code declares a
variable within the initialization
expression. The scope of this variable
extends from its declaration to the
end of the block governed by the for
statement, so it can be used in the
termination and increment expressions
as well. If the variable that controls
a for statement is not needed outside
of the loop, it's best to declare the
variable in the initialization
expression. The names i, j, and k are
often used to control for loops;
declaring them within the
initialization expression limits their
life span and reduces errors.
Source: http://download.oracle.com/javase/tutorial/java/nutsandbolts/for.html
