Cast Regular Int to Final Java

Question

I am trying to implement an inner class within a loop, and have come into an interesting situation. The internal class has methods, however, when I try and access the variable, Netbeans gives me a compiler error and tells me to make the int final.

As the int is a looping variable, it can not be final. I have tried creating new variables and equating them to the looping variable, but this still throws the same error.

Here is the basic syntax (in pseudo-code):

for(int i = 0; i < 10; i++)
{
     panels[i].printI(new printI(){System.out.println(i);});
}

Any ideas?

Can't you just use `final int j = i;` on the first line of the loop then, and pass `j` to `System.out.println`? — Daniël Knippers, Apr 18 '14 at 16:09
However, if I do this, then the loop would not be able to increment the j, because the value would be locked? — Jake Chasan, Apr 18 '14 at 16:38
Thanks for the reply. But why can an inner class not access a local variable that is above its scope? — Jake Chasan, Apr 18 '14 at 16:42

score 5 · Accepted Answer · answered Apr 18 '14 at 16:09

5

Add a temporary final variable to hold the value:

for(int i = 0; i < 10; i++)
{
     final int tmp = i;
     panels[i].printI(new printI(){System.out.println(tmp);});
}

answered Apr 18 '14 at 16:09

Didier L

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This answer provided a good solution that helped me. Thank you for posting. – Jake Chasan Apr 18 '14 at 16:49

score 4 · Answer 2 · answered Apr 18 '14 at 16:09

4

This is the idiom:

for(int i = 0; i < 10; i++)
{
  final int j = i;
  panels[i].printI(new printI(){System.out.println(j);});
}

answered Apr 18 '14 at 16:09

Giovanni Botta

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qqilihq · Answer 3 · 2014-04-18T16:45:15.967

0

Or use the array variant, which saves you one line of code ;)

for(final int[] i = {0}; i[0] < 10; i[0]++)
{
     panels[i[0]].printI(new printI(){System.out.println(i[0]);});
}

edited Apr 18 '14 at 16:45

answered Apr 18 '14 at 16:30

qqilihq

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oooo I like that one. Provides mutability without any performance penalty or complexity of a wrapping object. – captainroxors Apr 18 '14 at 16:36

Cast Regular Int to Final Java

3 Answers3

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