String

One thing that feels like it should implement the Iterable interface but does not is String.

class Main {
   void main() {
String letters = "abc";
for (char letter : letters) {
    System.out.println(letter);
}
   }
}

To loop over all the characters in a String, you have to use a regular loop.

class Main {
   void main() {
String letters = "abc";
for (int i = 0; i < letters.length(); i++) {
    char letter = letters.charAt(i);
    System.out.println(letter);
}
   }
}