Null check in an enhanced for loop

Question

What is the best way to guard against null in a for loop in Java    This seems ugly    if  someList    null        for  Object object   someList               do whatever           Or  if  someList    null        return     Or throw ex   for  Object object   someList           do whatever     There might not be any other way  Should they have put it in the for construct itself  if it is null then don t run the loop

User · Answer

It s already 2017  and you can now use Apache Commons Collections4  The usage    for Object obj   ListUtils emptyIfNull list1           Do your stuff     You can do the same null-safe check to other Collection classes with CollectionUtils emptyIfNull

User · Answer

Use ArrayUtils nullToEmpty from the commons-lang library for Arrays  for  Object o   ArrayUtils nullToEmpty list            do whatever      This functionality exists in the commons-lang library  which is included in most Java projects      ArrayUtils nullToEmpty source code  public static Object   nullToEmpty final Object   array        if  isEmpty array             return EMPTY OBJECT ARRAY            return array        ArrayUtils isEmpty source code public static boolean isEmpty final Object   array        return array    null    array length    0      This is the same as the answer given by  OscarRyz  but for the sake of the DRY mantra  I believe it is worth noting  See the commons-lang project page  Here is the nullToEmpty API documentation and source  Maven entry to include commons-lang in your project if it is not already     lt dependency gt       lt groupId gt org apache commons lt  groupId gt       lt artifactId gt commons-lang3 lt  artifactId gt       lt version gt 3 4 lt  version gt   lt  dependency gt    Unfortunately  commons-lang doesn t provide this functionality for List types  In this case you would have to use a helper method as previously mentioned   public static  lt E gt  List lt E gt  nullToEmpty List lt E gt  list        if list    null    list isEmpty                  return Collections emptyList              return list

User · Answer

You should better verify where you get that list from    An empty list is all you need  because an empty list won t fail   If you get this list from somewhere else and don t know if it is ok or not you could create a utility method and use it like this   for  Object o   safe  list             do whatever       And of course safe would be   public static List safe  List other         return other    null   Collections EMPTY LIST   other

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Use  CollectionUtils isEmpty Collection coll  method which is Null-safe check if the specified collection is empty    for this import org apache commons collections CollectionUtils   Maven dependency   lt dependency gt       lt groupId gt org apache commons lt  groupId gt       lt artifactId gt commons-collections4 lt  artifactId gt       lt version gt 4 0 lt  version gt   lt  dependency gt

User · Answer

You could potentially write a helper method which returned an empty sequence if you passed in null   public static  lt T gt  Iterable lt T gt  emptyIfNull Iterable lt T gt  iterable        return iterable    null   Collections  lt T gt emptyList     iterable      Then use   for  Object object   emptyIfNull someList         I don t think I d actually do that though - I d usually use your second form  In particular  the  or throw ex  is important - if it really shouldn t be null  you should definitely throw an exception  You know that something has gone wrong  but you don t know the extent of the damage  Abort early

User · Answer

For anyone uninterested in writing their own static null safety method you can use  commons-lang s org apache commons lang ObjectUtils defaultIfNull Object  Object   For example        for  final String item         List lt String gt  ObjectUtils defaultIfNull items  Collections emptyList               ObjectUtils defaultIfNull JavaDoc

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The  quot    quot  or the  quot    quot  comes in handy here Best choice and IE compatible is the    for  Object object   someList                 undefined and null gets defaulted to an empty array       Nullish coalescing operator  Not IE compatible for  Object object   someList                 undefined and null gets defaulted to an empty array

User · Answer

Another way to effectively guard against a null in a for loop is to wrap your collection with Google Guava s Optional lt T gt  as this  one hopes  makes the possibility of an effectively empty collection clear since the client would be expected to check if the collection is present with Optional isPresent

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for  Object object   someList           do whatever    throws the null pointer exception

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I have modified the above answer  so you don t need to cast from Object  public static  lt T gt  List lt T gt  safeClient  List lt T gt  other                 return other    null   Collections EMPTY LIST   other      and then simply call the List by  for  MyOwnObject ownObject   safeClient someList            do whatever     Explaination  MyOwnObject  If List lt Integer gt  then MyOwnObject will be Integer in this case

User · Answer

If you are getting that List from a method call that you implement  then don t return null  return an empty List   If you can t change the implementation then you are stuck with the null check  If it should t be null  then throw an exception   I would not go for the helper method that returns an empty list because it may be useful some times but then you would get used to call it in every loop you make possibly hiding some bugs

User · Answer

With Java 8 Optional   for  Object object   Optional ofNullable someList  orElse Collections emptyList              do whatever

[java] Null check in an enhanced for loop

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