How to convert Set String to String

Question

I need to get a String   out of a Set lt String gt   but I don t know how to do it  The following fails   Map lt String    gt  myMap   gpxlist getAll    Set lt String gt  myset   myMap keySet    String   GPXFILES1    String    myset toArray       Here it fails    How can I fix it so that it works

User · Accepted Answer

Use the Set toArray IntFunction lt T   gt   method taking an IntFunction as generator  String   GPXFILES1   myset toArray String    new    If you re not on Java 11 yet  then use the Set toArray T    method taking a typed array argument of the same size  String   GPXFILES1   myset toArray new String myset size       While still not on Java 11  and you can t guarantee that myset is unmodifiable at the moment of conversion to array  then better specify an empty typed array  String   GPXFILES1   myset toArray new String 0

User · Answer

In Java 11 we can use Collection toArray generator  method  The following code will create a new array of String   Set lt String gt  set   Set of  one    two    three    String   array   set toArray String    new    See  https   docs oracle com en java javase 11 docs api java base java util Collection html toArray java util function IntFunction

User · Answer

Set lt String gt  stringSet  new HashSet lt  gt     String   s    String   stringSet toArray

User · Answer

Java 11  The new default toArray method in Collection interface allows the elements of the collection to be transferred to a newly created array of the desired runtime type  It takes IntFunction lt T   gt  generator as argument and can be used as    String   array   set toArray String    new     There is already a similar method Collection toArray T    and this addition means we no longer be able to pass null as argument because in that case reference to the method would be ambiguous  But it is still okay since both methods throw a NPE anyways   Java 8  In Java 8 we can use streams API   String   array   set stream   toArray String    new     We can also make use of the overloaded version of toArray   which takes IntFunction lt A   gt  generator as   String   array   set stream   toArray n - gt  new String n      The purpose of the generator function here is to take an integer  size of desired array  and produce an array of desired size  I personally prefer the former approach using method reference than the later one using lambda expression

User · Answer

Use  toArray T   a  method   String   array   set toArray new String 0

User · Answer

I was facing the same situation   I begin by declaring the structures I need   Set lt String gt  myKeysInSet     null    String   myArrayOfString   null   In my case  I have a JSON object and I need all the keys in this JSON to be stored in an array of strings  Using the GSON library  I use JSON keySet   to get the keys and move to my Set    myKeysInSet   json any keySet     With this  I have a Set structure with all the keys  as I needed it  So I just need to the values to my Array of Strings  See the code below   myArrayOfString   myKeysInSet toArray new String myKeysInSet size       This was my first answer in StackOverflow   Sorry for any error  D

User · Answer

Guava style   Set lt String gt  myset   myMap keySet    FluentIterable from mySet  toArray String class     more info  https   google github io guava releases 19 0 api docs com google common collect FluentIterable html

[java] How to convert Set<String> to String[]?

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