一、场景
我们知道String类有分割字符串的作用（subString函数），当然在List集合里面也提供了分割集合的作用（subList函数）。
但List的这个分割方法有坑啊，如下面代码：
1、正常使用：
ArrayList<String> arrayList = new ArrayList<>();
arrayList.add("a");
arrayList.add("b");
arrayList.add("c");
arrayList.add("d");
List<String> list = arrayList.subList(0, 2);
System.out.println(list);输出：
2、带坑的使用：
List<String> arrayList = new ArrayList<String>();
arrayList.add("a");
arrayList.add("b");
arrayList.add("c");
List<String> arrayList_subList = arrayList.subList(0, 2);
arrayList.remove(0);
arrayList.add("d");
System.out.println(arrayList_subList.size());输出：
最后一行报错。按正常的代码逻辑思维，arrayList_subList新建了一个新对象List，保存分割的数据，后续父List的改变应该不影响子List的，但是不是的。
二、原因分析：
看这个函数的官方文档：
/**
* Returns a view of the portion of this list between the specified
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
* {@code fromIndex} and {@code toIndex} are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations supported
* by this list.<p>
*
* This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>{@code
* list.subList(from, to).clear();
* }</pre>
* Similar idioms may be constructed for {@code indexOf} and
* {@code lastIndexOf}, and all of the algorithms in the
* {@code Collections} class can be applied to a subList.<p>
*
* The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
* @throws IndexOutOfBoundsException for an illegal endpoint index value
* ({@code fromIndex < 0 || toIndex > size ||
* fromIndex > toIndex})
*/
根据注释得知：
1，该方法返回的是父list的一个视图，从fromIndex（包含），到toIndex（不包含）。fromIndex=toIndex 表示子list为空
2，父子list做的非结构性修改（non-structural changes）都会影响到彼此：所谓的“非结构性修改”，是指不涉及到list的大小改变的修改。相反，结构性修改，指改变了list大小的修改。
3，对于结构性修改，子list的所有操作都会反映到父list上。但父list的修改将会导致返回的子list失效。
4，tips：如何删除list中的某段数据：
list.subList(from, to).clear();
下面一段代码验证第三点：
List<String> list = new ArrayList<String>();
list.add("a");
// 使用构造器创建一个包含list的列表list1
List<String> list1 = new ArrayList<String>(list);
// 使用subList生成与list相同的列表list2
List<String> list2 = list.subList(0, list.size());
list2.add("b");
System.out.println(list.equals(list1));
System.out.println(list.equals(list2));输出：
三、总结
多看源码。