Most concise way to convert a Set T to a List T

Question

For example  I am currently doing this   Set lt String gt  setOfTopicAuthors         List lt String gt  list   Arrays asList       setOfTopicAuthors toArray  new String 0         Can you beat this

User · Accepted Answer

List lt String gt  list   new ArrayList lt String gt  listOfTopicAuthors

User · Answer

not really sure what you re doing exactly via the context of your code but     why make the listOfTopicAuthors variable at all   List lt String gt  list   Arrays asList        toArray  new String 0         the        represents however your set came into play  whether it s new or came from another location

User · Answer

If you are using Guava  you statically import newArrayList method from Lists class   List lt String gt  l   newArrayList setOfAuthors

User · Answer

List lt String gt  l   new ArrayList lt String gt  listOfTopicAuthors

User · Answer

Considering that we have Set lt String gt  stringSet we can use following  Plain Java List lt String gt  strList   new ArrayList lt  gt  stringSet    Guava List lt String gt  strList   Lists newArrayList stringSet    Apache Commons List lt String gt  strList   new ArrayList lt  gt     CollectionUtils addAll strList  stringSet    Java 10  Unmodifiable List  List lt String gt  strList   List copyOf stringSet   List lt String gt  strList   stringSet stream   collect Collectors toUnmodifiableList      Java 8  Modifiable Lists  import static java util stream Collectors    List lt String gt  stringList1   stringSet stream   collect toList      As per the doc for the method toList    There are no guarantees on the type  mutability  serializability  or thread-safety of the List returned  if more control over the returned List is required  use toCollection Supplier    So if we need a specific implementation e g  ArrayList we can get it this way  List lt String gt  stringList2   stringSet stream                                  collect toCollection ArrayList  new     Java 8  Unmodifiable Lists  We can make use of Collections  unmodifiableList method and wrap the list returned in previous examples  We can also write our own custom method as  class ImmutableCollector       public static  lt T gt  Collector lt T  List lt T gt   List lt T gt  gt  toImmutableList Supplier lt List lt T gt  gt  supplier                return Collector of  supplier  List  add   left  right  - gt                            left addAll right                           return left                         Collections  unmodifiableList                And then use it as  List lt String gt  stringList3   stringSet stream                 collect ImmutableCollector toImmutableList ArrayList  new      Another possibility is to make use of collectingAndThen method which allows some final transformation to be done before returning result      List lt String gt  stringList4   stringSet stream   collect collectingAndThen        toCollection ArrayList  new  Collections  unmodifiableList      One point to note is that the method Collections  unmodifiableList returns an unmodifiable view of the specified list  as per doc  An unmodifiable view collection is a collection that is unmodifiable and is also a view onto a backing collection  Note that changes to the backing collection might still be possible  and if they occur  they are visible through the unmodifiable view  But the collector method Collectors unmodifiableList returns truly immutable list in Java 10

User · Answer

Try this for Set   Set lt String gt  listOfTopicAuthors         List lt String gt  setList   new ArrayList lt String gt  listOfTopicAuthors      Try this for Map   Map lt String  String gt  listOfTopicAuthors            List of values  List lt String gt  mapValueList   new ArrayList lt String gt  listOfTopicAuthors values        List of keys  List lt String gt  mapKeyList   new ArrayList lt String gt  listOfTopicAuthors KeySet

[java] Most concise way to convert a Set<T> to a List<T>

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