Page 1215 - AP Computer Science A, 7th edition

13. (B) The remove method of ArrayList removes the indicated element, shifts the remaining elements down one slot (i.e., it does not leave gaps in the list), and adjusts the size of the list. Consider the list in choice B. The index values are shown:
The cat cat sat on the mat 0123456
After the first occurrence of cat has been removed:
The cat sat on the mat mat
0123456
The value of i, which was 1 when cat was removed, has now been incremented to 2 in the for loop. This means that the word to be considered next is sat. The second occurrence of cat has been missed. Thus, the given code will fail whenever occurrences of the word to be removed are consecutive. You fix it by not allowing the index to increment when a removal occurs:
int i = 0;
while (i < wordList.size()) {
if ((wordList.get(i)).equals(word)) wordList.remove(i);
else
i++; }