List截取

男娘i 2022-03-22 04:14 236阅读 0赞

/** * 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位数 * @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，用返回值来指定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);
                }
            }
        }