When you need to carry out a sentence LIst air operations we can use the following two statements:
if (list == null || list.size() == 0) {}
if (list != null && list.size() != 0) {}
Some may doubt if they meet list == null, then this list is not to empty it? Why then use another condition list.size == 0 it?
First, we need to understand two conditions represent what meanings:
1. list == null: determining a list has not been initialized, i.e. whether the list is assigned is null, as List list = null;, satisfies this condition, then the list is no data
2. list.size == 0: used for determining whether there is data in the list, the list satisfies this condition is no data
If only list == null: Once the list is initialized List list2 = new ArrayList (); , this time is no longer null list, but the list is not data. If only list == null to determine whether it is empty, it will be an error of judgment.
If only list .size == 0: If the list is not initialized, null pointer error will be reported when using this condition, you can not reach sentenced empty goal. Therefore, when the use conditions, must be determined whether the initialization list
to sum up:
When the List were sentenced empty, it requires two conditions: first use list == null to determine whether the list after initialization, re-use if the list .size == 0 judgment is empty.
Reference link: https: //www.cnblogs.com/huiAlex/p/8594270.html