Filter values only if not null using lambda in Java8

Question

I have a list of objects say car  I want to filter this list based on some parameter using Java 8  But if the parameter is null  it throws NullPointerException  How to filter out null values   Current code is as follows  requiredCars   cars stream   filter c - gt  c getName   startsWith  M       This throws NullPointerException if getName   returns null

User · Answer

Leveraging the power of java util Optional map     List lt Car gt  requiredCars   cars stream      filter  car - gt       Optional ofNullable car         map Car  getName         map name - gt  name startsWith  M           orElse false     what to do if either car or getName   yields null  false will filter out the element          collect Collectors toList

User · Answer

The proposed answers are great  Just would like to suggest an improvement to handle the case of null list using Optional ofNullable  new feature in Java 8    List lt String gt  carsFiltered   Optional ofNullable cars                   orElseGet Collections  emptyList                   stream                    filter Objects  nonNull                   collect Collectors toList       So  the full answer will be    List lt String gt  carsFiltered   Optional ofNullable cars                   orElseGet Collections  emptyList                   stream                    filter Objects  nonNull    filtering car object that are null                  map Car  getName    now it s a stream of Strings                  filter Objects  nonNull    filtering null in Strings                  filter name - gt  name startsWith  M                     collect Collectors toList       back to List of Strings

User · Answer

In this particular example I think  Tagir is 100  correct get it into one filter and do the two checks   I wouldn t use Optional ofNullable the Optional stuff is really for return types not to be doing logic    but really neither here nor there   I wanted to point out that java util Objects has a nice method for this in a broad case  so you can do this   cars stream        filter Objects  nonNull    Which will clear out your null objects   For anyone not familiar  that s the short-hand for the following   cars stream        filter car - gt  Objects nonNull car     To partially answer the question at hand to return the list of car names that starts with  M    cars stream        filter car - gt  Objects nonNull car        map car - gt  car getName         filter carName - gt  Objects nonNull carName        filter carName - gt  carName startsWith  M         collect Collectors toList       Once you get used to the shorthand lambdas you could also do this   cars stream        filter Objects  nonNull       map Car  getName            Assume the class name for car is Car      filter Objects  nonNull       filter carName - gt  carName startsWith  M         collect Collectors toList       Unfortunately once you  map Car  getName  you ll only be returning the list of names  not the cars   So less beautiful but fully answers the question   cars stream        filter car - gt  Objects nonNull car        filter car - gt  Objects nonNull car getName          filter car - gt  car getName   startsWith  M         collect Collectors toList

User · Answer

You can do this in single filter step   requiredCars   cars stream   filter c - gt  c getName      null  amp  amp  c getName   startsWith  M       If you don t want to call getName   several times  for example  it s expensive call   you can do this   requiredCars   cars stream   filter c - gt        String name   c getName        return name    null  amp  amp  name startsWith  M          Or in more sophisticated way   requiredCars   cars stream   filter c - gt       Optional ofNullable c getName    filter name - gt  name startsWith  M    isPresent

User · Answer

you can use this  List lt Car gt  requiredCars   cars stream        filter  t- gt   t   null  amp  amp  StringUtils startsWith t getName    M         collect Collectors toList

User · Answer

You just need to filter the cars that have a null name   requiredCars   cars stream                       filter c - gt  c getName      null                      filter c - gt  c getName   startsWith  M

[java] Filter values only if not null using lambda in Java8

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