Java集合中二分查找算法实现

public static <T>
    int binarySearch(List<? extends Comparable<? super T>> list, T key) {
        if (list instanceof RandomAccess || list.size()< BINARYSEARCH_THRESHOLD)
            return Collections. indexedBinarySearch(list, key);
        else
            return Collections. iteratorBinarySearch(list, key);
    }


private static <T>
    int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key ) {
        int low = 0;
        int high = list.size()-1;

        while (low <= high) {
            int mid = ( low + high) >>> 1;
            Comparable<? super T> midVal = list.get( mid);
            int cmp = midVal.compareTo( key);

            if ( cmp < 0)
                low = mid + 1;
            else if ( cmp > 0)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1);  // key not found
    }

    private static <T>
    int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key )
    {
        int low = 0;
        int high = list.size()-1;
        ListIterator<? extends Comparable<? super T>> i = list.listIterator();

        while (low <= high) {
            int mid = ( low + high) >>> 1;
            Comparable<? super T> midVal = get(i , mid );
            int cmp = midVal.compareTo( key);

            if ( cmp < 0)
                low = mid + 1;
            else if ( cmp > 0)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1);  // key not found
    }

 /**
     * Gets the ith element from the given list by repositioning the specified
     * list listIterator.
     */
    private static <T> T get(ListIterator<? extends T> i, int index) {
        T obj = null;
        int pos = i.nextIndex();
        if (pos <= index) {
            do {
                obj = i.next();//链表移动
            } while ( pos++ < index);
        } else {
            do {
                obj = i.previous();
            } while (-- pos > index);
        }
        return obj;
    }