Effective Java-----Returns an array or collection of 0 lengths instead of NULL

The following code, which normally returns NULL when the user list is empty, is assumed to be that the null return value is better than a zero-length array because it avoids the overhead required to allocate the array.

Private final list<userbean> userlist = null;public list<userbean> Getuserbean () {    if (userlist.size () = = 0) {        return null;    } else{        return userlist;}    }

But this view is untenable for the following reasons:

1) It is unwise to worry about performance issues at this level unless the analysis shows that this approach is the real source of performance problems;
2) It is possible to return a 0-length array every time for calls that do not return any elements, since 0-length arrays are immutable, and immutable objects may be freely shared.

Therefore, you can return a collection of 0 lengths as follows:

Public list<userbean> getuserbeanmodify () {    if (Userlist.isempty ()) {        return collections.emptylist ();    } else{        return userlist;}    }

In summary, it is important to note that the return type is an array or a method of a collection, and there is no reason to return null, but to return a 0-length arrays or collections.

Effective Java-----Returns an array or collection of 0 lengths instead of NULL