/** * Returns the description of the {@code number}. This method distinguishes the case of an invalid * prefix and a prefix for which the name is not available in the current language. If the * description is not available in the current language an empty string is returned. If no * description was found for the provided number, null is returned. * * @param number the phone number to look up * @return the description of the number */ String lookup(long number) { int numOfEntries = phonePrefixMapStorage.getNumOfEntries(); if (numOfEntries == 0) { return null; } long phonePrefix = number; int currentIndex = numOfEntries - 1; SortedSet<Integer> currentSetOfLengths = phonePrefixMapStorage.getPossibleLengths(); while (currentSetOfLengths.size() > 0) { Integer possibleLength = currentSetOfLengths.last(); String phonePrefixStr = String.valueOf(phonePrefix); if (phonePrefixStr.length() > possibleLength) { phonePrefix = Long.parseLong(phonePrefixStr.substring(0, possibleLength)); } currentIndex = binarySearch(0, currentIndex, phonePrefix); if (currentIndex < 0) { return null; } int currentPrefix = phonePrefixMapStorage.getPrefix(currentIndex); if (phonePrefix == currentPrefix) { return phonePrefixMapStorage.getDescription(currentIndex); } currentSetOfLengths = currentSetOfLengths.headSet(possibleLength); } return null; }
/** * Does a binary search for {@code value} in the provided array from {@code start} to {@code end} * (inclusive). Returns the position if {@code value} is found; otherwise, returns the position * which has the largest value that is less than {@code value}. This means if {@code value} is the * smallest, -1 will be returned. */ private int binarySearch(int start, int end, long value) { int current = 0; while (start <= end) { current = (start + end) >>> 1; int currentValue = phonePrefixMapStorage.getPrefix(current); if (currentValue == value) { return current; } else if (currentValue > value) { current--; end = current; } else { start = current + 1; } } return current; }