Which of the following 5 implementations could not be used for contains?

• public boolean contains(T anEntry) { boolean found = false; int i = 0; while ( !found && (i < numberOfEntries)) { if (anEntry.equals(contents[i])) { found = true; } i++; } return found; }
• public boolean contains(T anEntry) { return getIndexOf(anEntry) > -1; }
• public boolean contains(T anEntry) { return getFrequencyOf(anEntry) > 0; }
• public boolean contains(T anEntry) { int i = 0; while ((i < numberOfEntries)) { if (anEntry.equals(contents[i])) { return true; } i++; } return false; }