Redeclaring a Variable in the Initialization Block

[Suni Leeg]

Hi everyone,

Is someone able to explain the below statement? I'm having trouble understanding the difference between the two examples and why the second one would compile?

Thanks

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Redeclaring a Variable in the Initialization Block

int x = 0;
for(long y = 0, x = 4; x < 5 && y < 10; x++, y++) {   // DOES NOT COMPILE
  System.out.print(x + " ");
}

This example looks similar to the previous one, but it does not compile because of the initialization block. The difference is that x is repeated in the initialization block after already being declared before the loop, resulting in the compiler stopping because of a duplicate variable declaration. We can fix this loop by changing the declaration of x and y as follows:

int x = 0;
long y = 10;
for(y = 0, x = 4; x < 5 && y < 10; x++, y++) {
  System.out.print(x + " ");
}

Note that this variation will now compile because the initialization block simply assigns a value to x and does not declare it.

[Tim Holloway]

Basically, the first clause of the "for" statement can either be an assignment statement or a declaration statement. So "int y =0, x=0" is an assignment statement, leading to the effect of the following:

int x=0;
int y=0;
int x=0;
for ( ; …; …) {
}

Here the double-declaration is obvious. You can define and optionally assign multiple variables in an assignment statement, so "int y=0, x=0;" is equivalent to "int y =0; int x=0;" and NOT a declaration of y followed by an assignment without declaration of x.

As a rule, defining multiple variables in a single definition statement isn't encouraged these days.

[Campbell Ritchie]

Tim Holloway wrote:. . . defining multiple variables in a single definition statement isn't encouraged . . .

I would have preferred that  to have been encouraged at all

[Liutauras Vilda]

@OP

Is it Java Certification of some sort question? If yes, then I'd move (maybe copy) your question to another forum, we have a dedicated ones.

[Suni Leeg]

Thanks for the replies - i understand now.

Yes it is for OCA certification

I'm not sure how to move my post but i will use the dedicated forums in future - thanks for letting me know.