Java 8 Lambda filter by Lists

Question

I have two list and i want filter thoose elements which are both list contains  And i want to do this with lambda expression   Users getName and Clients getUserName both are return with String   Here is my sample code   List lt Client gt  clients   new ArrayList lt  gt     List lt User gt  users   new ArrayList lt  gt     List lt Client gt  results   new ArrayList lt  gt      for  Client user   users        for Client client  clients           if user getName   equals client getUserName                  result add client

User · Answer

Something like   clients stream filter c- gt      users stream filter u- gt u getName   equals c getName    count   gt 0    collect Collectors toList       This is however not an awfully efficient way to do it  Unless the collections are very small  you will be better of building a set of user names and using that in the condition

User · Answer

Look this   List lt Client gt  result   clients      stream        filter c - gt            users stream   map User  getName  collect Collectors toList     contains c getName              collect Collectors toList

User · Answer

Predicate lt Client gt  hasSameNameAsOneUser        c - gt  users stream   anyMatch u - gt  u getName   equals c getName       return clients stream                  filter hasSameNameAsOneUser                 collect Collectors toList       But this is quite inefficient  because it s O m   n   You d better create a Set of acceptable names   Set lt String gt  acceptableNames        users stream             map User  getName            collect Collectors toSet      return clients stream                  filter c - gt  acceptableNames contains c getName                    collect Collectors toList       Also note that it s not strictly equivalent to the code you have  if it compiled   which adds the same client twice to the list if several users have the same name as the client

User · Answer

I would like share an example to understand the usage of stream   filter  Code Snippet  Sample program to identify even number   import java util ArrayList  import java util List  import java util stream Collectors   public void fetchEvenNumber            List lt Integer gt  numberList   new ArrayList lt  gt             numberList add 10           numberList add 11           numberList add 12           numberList add 13           numberList add 14           numberList add 15            List lt Integer gt  evenNumberListObj   numberList stream   filter i - gt  i 2    0  collect Collectors toList             System out println evenNumberListObj       Output will be    10  12  14   List evenNumberListObj   numberList stream   filter i -  i 2    0  collect Collectors toList      numberList  it is an ArrayList object contains list of numbers   java util Collection stream     stream   will get the stream of collection  which will return the Stream of Integer   filter   Returns a stream that match the given predicate  i e based on given condition  i -  i 2    0  returns the matching stream   collect  whatever the stream of Integer filter based in the filter condition  those integer will be put in a list

[java] Java 8 Lambda filter by Lists

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