List截取

    /**
     * 截取list，保留前l位
     * Examples:
     * list = [0, 1, 2, 3, 4, 5]
     * subList(list, 3);
     * list = [0, 1, 2]
     *
     * @param list      待截取list
     * @param newLength 保留前length位數
     * @param <T>
     */
    public static <T> void subList(List<T> list, int newLength) {
        if (null == list || newLength < 0 || newLength > list.size()) {
            return;
        }
        for (int i = list.size() - 1; i >= newLength; i--) {
            T t = list.remove(i);//避免List<Integer>的元素和index混淆，用返回值來指定API方法
        }
    }

    /**
     * Get a List that is a subList of this List. The
     * subList begins at the specified {@code beginIndex} and
     * extends to the element at index {@code endIndex - 1}.
     * Thus the length of the subList is {@code endIndex-beginIndex}.
     * <p>
     * Examples:
     * list = [0, 1, 2, 3, 4, 5]
     * subList(list, 0 , 3);
     * list = [0, 1, 2]
     *
     * @param beginIndex the beginning index, inclusive.
     * @param endIndex   the ending index, exclusive.
     * @exception  IndexOutOfBoundsException  if the
     *             {@code beginIndex} is negative, or
     *             {@code endIndex} is larger than the length of
     *             this {@code list} object, or
     *             {@code beginIndex} is larger than
     *             {@code endIndex}.
     */

    public static <T> void subList(List<T> list, int beginIndex, int endIndex) {
        if (list == null || list.size() == 0) return;
        if (beginIndex < 0) {
            throw new ArrayIndexOutOfBoundsException(beginIndex);
        }
        int size = list.size();
        if (endIndex > size) {
            throw new ArrayIndexOutOfBoundsException(endIndex);
        }
        int subLen = endIndex - beginIndex;
        if (subLen < 0) {
            throw new ArrayIndexOutOfBoundsException(subLen);
        }

        for (int i = size - 1; i >= 0; i--) {
            if (i >= endIndex || i < beginIndex) {
                T t = list.remove(i);
            }
        }
    }