For beginners + This article has a lot of personal opinions.
When I'm doing code reviews, I sometimes see
List list =Some process / method [List is returned]; //NULL and empty check if [list == null || list.size[] == 0] { }It is a code that performs NULL / empty check of List.
There is no problem in operation. However, I don't like it so much, so I may ask you to fix it. There are mainly ** two ** reasons.
First of all, I would like you to check if the list variable may be set to NULL in "Some process / method".
If you can make it NULL, you should fix the process there.
why?
This is to reduce the possibility of a NullPointerException. You can also eliminate the caller's null check.
If "some process / method" is common, all callers must check for NULL. If the caller does not check for NULL, there is a risk of getting a NullPointerException.
If it never returns NULL, the method caller does not have to assume that it will return NULL. The caller implementation will be a little easier.
Remove all the elements in the list using remove []` `` or removeAll []` ``, etc.
Collections.emptyList[]Let's return an empty list with something like that.
It is also a good idea to add final to the List declaration. * I told you in the comments. # Second: I want you to use isEmpty [] instead of size == 0 Is this a personal hobby? opinion? is. #### **`list.size ==List instead of 0.isEmpty[]I want you to.`**why?
I think there is an opinion that "the contents ofʻis Empty []`` is size == 0 `` !!!". That's right at all. Nothing changes as the processing content.
But isn't list.isEmpty []` `` easier to understand than` `list.size == 0 ...? Perhaps `list.isEmpty []` is easier for non-Java programmers to understand, "I'm checking if it's empty!".
I want you to stop the NULL check and only check the empty of isEmpty [] `` `. To avoid the need for NULL checking, never return NULL in "some process / method", even if it returns an empty list.size[] == 0Than,isempty[]Is more readable**I personally think**Soisempty[]```to use.
List list =Some process / method [List is returned]; //Empty check only if [list.isEmpty[]] { }Occasionally, there is a code that judges with ``` &&` `` as shown below, but be careful because it will be a NullPointerException if NULL comes.
if[list == null && list.size[] == 0]{}Apparently in the training for new employees[list == null || list.size[] == 0]It seems that he was taught. I'm not wrong, but ... I was sick of it, so I wrote an article. [What do you mean?