Question

I am trying to create an item list, diffrent for each i and j variable. My code is:

if (i == 0) { 
            if (j == 0) { 
                final CharSequence[] items = {"4:45", "5:00"}
            } else if (j == 1) { 
                final CharSequence[] items = {"4:43", "4:58"}
            } else if (j == 2) { 
                final CharSequence[] items = {"4:41", "4:56"}
            } else { 
                final CharSequence[] items = {"4:38", "4:53"}
}

…

new AlertDialog.Builder(this)
               .setTitle("Hours")
               .setItems(items,
                new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialoginterface, int i) {
                      // getStation(i);
                   }
                })
               .show();
       }

I get an error in the line .setItems(items,:

items cannot be resolved

I think that the compiler thinks that the CharSequence[] items may not be initialised or something…
How can I make this programme run?

Answer 1

The problem is variable scoping.

if (someCondition) {
   final int i = 666;
} else {
   final int i = 42;
}
int j = i + 1; // compile-time error

Here we have two local variables i who goes out of scope immediately after they’re declared and initialized. If j needs the value of i, then i would have to be declared in a larger scope.

final int i;
if (someCondition) {
   i = 666;
} else {
   i = 42;
}
int j = i + 1; // compiles fine!

(It should be mentioned that this is exactly the kind of scenarios where the ternary operator excels, i.e.)

final int i = (someCondition) ? 666 : 42;

---

In your specific case, unfortunately the array initializer shorthand can only be used to initialize upon declaration. That is:

int[] arr1 = { 1, 2, 3 }; // compiles fine!
int[] arr2;
arr2 = { 4, 5, 6 }; // doesn't compile!

You can pull out the declaration of items outside the if and write the verbose code for each case (see Joachim Sauer’s answer), but a more concise code is to use array-of-arrays instead.

final CharSequence[][] allItems = {
   { "4:45", "5:00" },
   { "4:43", "4:58" },
   { "4:41", "4:56" },
   { "4:38", "4:53" }
};
final CharSequence[] items = allItems[j];

This technique works well in this case, but in the more general case you want to use a Map or something similar.

Note: It’s not explicit in the original code, but this works if j can either be 0, 1, 2, or 3. If you want the last option to apply when j is any value other than 0, 1, 2, then you have to check for that and set it to 3 before this code.