Is there a way to avoid null check before the for-each loop iteration starts

Question

Every time I have to iterate over a collection I end up checking for null  just before the iteration of the for-each loop starts  Like this   if  list1    null        for Object obj   list1              Is there a shorter way  so that we can avoid writing the  if  block   Note  I am using Java 5  and will be stuck with it for sometime

User · Answer

1  if list1 is a member of a class  create the list in the constructor so it s there and non-null though empty   2  for  Object obj   list1    null   list1   new ArrayList

User · Answer

It s already 2017  and you can now use Apache Commons Collections4  The usage    for Object obj   CollectionUtils emptyIfNull list1           Do your stuff

User · Answer

How much shorter do you want it to be  It is only an extra 2 lines AND it is clear and concise logic   I think the more important thing you need to decide is if null is a valid value or not  If they are not valid  you should write you code to prevent it from happening  Then you would not need this kind of check  If you go get an exception while doing a foreach loop  that is a sign that there is a bug somewhere else in your code

User · Answer

Another Java 8  way would be to create a forEach method that does not crash when using a null value   public static  lt T gt  void forEach Iterable lt T gt  set  Consumer lt T gt  action        if  set    null            set forEach action             The usage of the own defined foreach is close to the native Java 8 one   ArrayList lt T gt  list   null     java 8   will throw a NullPointerException  list forEach item - gt  doSomething            own implementation forEach list  item - gt  doSomething

User · Answer

If possible  you should design your code such that the collections aren t null in the first place   null collections are bad practice  for this reason   you should use empty collections instead   eg  Collections emptyList     Alternatively  you could make a wrapper class that implements Iterable and takes a collections  and handles a null collection  You could then write foreach T obj   new Nullable lt T gt  list1

User · Answer

In Java 8 there is another solution available by using java util Optional and the ifPresent-method   Optional ofNullable list1  ifPresent l - gt  l forEach item - gt      do stuff          So  not a solution for the exact problem but it is a oneliner and possibly more elegant

User · Answer

public  lt T extends Iterable gt  T nullGuard T item      if  item    null        return Collections EmptyList      else       return item         or  if saving lines of text is a priority  it shouldn t be  public  lt T extends Iterable gt  T nullGuard T item      return  item    null    Collections EmptyList   item     would allow you to write for  Object obj   nullGuard list              Of course  this really just moves the complexity elsewhere

User · Answer

Null check in an enhanced for loop  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

User · Answer

Apache Commons  for  String code  ListUtils emptyIfNull codes                     Google Guava  for  String code  Optional of codes  get

User · Answer

I guess the right answer is that  there is no way to make it shorter  There are some techniques such as the ones in the comments  but I don t see myself using them  I think it s better to write a  if  block than to use those techniques  and yes   before anybody mentions it yet again     ideally  the code should be desgined such that list should never be a null

[java] Is there a way to avoid null check before the for-each loop iteration starts?

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