Java 8 merge lists with stream API

Question

I have the following situation  Map lt Key  ListContainer gt  map    public class ListContainer    List lt AClass gt  lst      I have to merge all the lists lst from the ListContainer objects from a Map map   public static void main String args        List lt AClass gt  alltheObjectsAClass   map values   stream       continue             Any idea how  using Java 8 stream API

User · Answer

In Java 8 we can use stream List1 stream   collect Collectors toList    addAll List2   Another option List1 addAll List2

User · Answer

Alternative  Stream concat    Stream concat map values   stream    listContainer lst stream                                  collect Collectors toList

User · Answer

I think flatMap   is what you re looking for   For example    List lt AClass gt  allTheObjects   map values             stream             flatMap listContainer - gt  listContainer lst stream              collect Collectors toList

User · Answer

Already answered above  but here s another approach you could take  I can t find the original post I adapted this from  but here s the code for the sake of your question  As noted above  the flatMap   function is what you d be looking to utilize with Java 8  You can throw it in a utility class and just call  quot RandomUtils combine list1  list2        quot  and you d get a single List with all values  Just be careful with the wildcard - you could change this if you want a less generic method  You can also modify it for Sets - you just have to take care when using flatMap   on Sets to avoid data loss from equals hashCode methods due to the nature of the Set interface  Edit - If you use a generic method like this for the Set interface  and you happen to use Lombok  make sure you understand how Lombok handles equals hashCode generation              Combines multiple lists into a single list containing all elements of       every list                param  lt T gt  - The type of the lists         param lists - The group of List implementations to combine        return a single List lt   gt  containing all elements of the passed in lists            public static  lt T gt  List lt   gt  combine final List lt   gt     lists          return Stream of lists  flatMap List  stream  collect Collectors toList

[java] Java 8: merge lists with stream API

Examples related to java

Examples related to list

Examples related to java-8

Examples related to java-stream