Proper usage of Optional ifPresent

Question

I am trying to understand the ifPresent   method of the Optional API in Java 8   I have simple logic   Optional lt User gt  user     user ifPresent doSomethingWithUser user get        But this results in a compilation error    ifPresent java util functionError  186  74  java   void  type not allowed here    Of course I can do something like this   if user isPresent        doSomethingWithUser user get         But this is exactly like a cluttered null check   If I change the code into this    user ifPresent new Consumer lt User gt                   Override public void accept User user                    doSomethingWithUser user get                                 The code is getting dirtier  which makes me think of going back to the old null check   Any ideas

User · Answer

Why write complicated code when you could make it simple?

Indeed, if you are absolutely going to use the Optional class, the most simple code is what you have already written ...

if (user.isPresent())
{
    doSomethingWithUser(user.get());
}

This code has the advantages of being

readable
easy to debug (breakpoint)
not tricky

Just because Oracle has added the Optional class in Java 8 doesn't mean that this class must be used in all situation.

User · Answer

Optional lt User gt  ifPresent   takes a Consumer lt   super User gt  as argument  You re passing it an expression whose type is void  So that doesn t compile    A Consumer is intended to be implemented as a lambda expression   Optional lt User gt  user       user ifPresent theUser - gt  doSomethingWithUser theUser      Or even simpler  using a method reference   Optional lt User gt  user       user ifPresent this  doSomethingWithUser     This is basically the same thing as  Optional lt User gt  user       user ifPresent new Consumer lt User gt           Override     public void accept User theUser            doSomethingWithUser theUser               The idea is that the doSomethingWithUser   method call will only be executed if the user is present  Your code executes the method call directly  and tries to pass its void result to ifPresent

User · Answer

In addition to  JBNizet s answer  my general use case for ifPresent is to combine  isPresent   and  get     Old way   Optional opt   getIntOptional    if opt isPresent          Integer value   opt get           do something with value     New way   Optional opt   getIntOptional    opt ifPresent value - gt           do something with value      This  to me  is more intuitive

User · Answer

You can use method reference like this   user ifPresent ClassNameWhereMethodIs  doSomethingWithUser     Method ifPresent   get Consumer object as a paremeter and  from JavaDoc    If a value is present  invoke the specified consumer with the value   Value it is your variable user   Or if this method doSomethingWithUser is in the User class and it is not static  you can use method reference like this   user ifPresent this  doSomethingWithUser

User · Answer

Use flatMap  If a value is present  flatMap returns a sequential Stream containing only that value  otherwise returns an empty Stream  So there is no need to use ifPresent     Example   list stream   map data - gt  data getSomeValue  map this  getOptinalValue  flatMap Optional  stream  collect Collectors toList

[java] Proper usage of Optional.ifPresent()

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