How to convert an Array to a Set in Java

Question

I would like to convert an array to a Set in Java  There are some obvious ways of doing this  i e  with a loop  but I would like something a bit neater  something like   java util Arrays asList Object   a     Any ideas

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Java 8   String   strArray     eins    zwei    drei    vier     Set lt String gt  strSet   Arrays stream strArray  collect Collectors toSet     System out println strSet       eins  vier  zwei  drei

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In Eclipse Collections  the following will work   Set lt Integer gt  set1   Sets mutable of 1  2  3  4  5   Set lt Integer gt  set2   Sets mutable of new Integer   1  2  3  4  5    MutableSet lt Integer gt  mutableSet   Sets mutable of 1  2  3  4  5   ImmutableSet lt Integer gt  immutableSet   Sets immutable of 1  2  3  4  5    Set lt Integer gt  unmodifiableSet   Sets mutable of 1  2  3  4  5  asUnmodifiable    Set lt Integer gt  synchronizedSet   Sets mutable of 1  2  3  4  5  asSynchronized    ImmutableSet lt Integer gt  immutableSet   Sets mutable of 1  2  3  4  5  toImmutable      Note  I am a committer for Eclipse Collections

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I ve written the below from the advice above - steal it    it s nice          Handy conversion to set     public class SetUtil                  Convert some items to a set         param items items         param  lt T gt  works on any type         return a hash set of the input items             public static  lt T gt  Set lt T gt  asSet T     items            return Stream of items  collect Collectors toSet

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Quickly   you can do       Fixed-size list List list   Arrays asList array       Growable list list   new LinkedList Arrays asList array        Duplicate elements are discarded Set set   new HashSet Arrays asList array      and to reverse     Create an array containing the elements in a list Object   objectArray   list toArray    MyClass   array    MyClass   list toArray new MyClass list size          Create an array containing the elements in a set objectArray   set toArray    array    MyClass   set toArray new MyClass set size

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new HashSet lt Object gt  Arrays asList Object   a     But I think this would be more efficient   final Set s   new HashSet lt Object gt         for  Object o   a    s add o

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After you do Arrays asList array  you can execute Set set   new HashSet list    Here is a sample method  you can write   public  lt T gt  Set lt T gt  GetSetFromArray T   array        return new HashSet lt T gt  Arrays asList array

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Sometime using some standard libraries helps a lot  Try to look at the Apache Commons Collections  In this case your problems is simply transformed to something like this  String   keys     blah    blahblah   Set lt String gt  myEmptySet   new HashSet lt String gt     CollectionUtils addAll pythonKeywordSet  keys     And here is the CollectionsUtils javadoc

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In Java 10   String   strs     A    B    Set lt String gt  set   Set copyOf Arrays asList strs      Set copyOf returns an unmodifiable Set containing the elements of the given Collection    nbsp The given Collection must not be null  and it must not contain any null elements

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Use CollectionUtils or ArrayUtils from stanford-postagger-3 0 jar   import static edu stanford nlp util ArrayUtils asSet  or  import static edu stanford nlp util CollectionUtils asSet         String    array     1    q    Set lt String gt  trackIds   asSet array

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Like this   Set lt T gt  mySet   new HashSet lt  gt  Arrays asList someArray      In Java 9   if unmodifiable set is ok   Set lt T gt  mySet   Set of someArray     In Java 10   the generic type parameter can be inferred from the arrays component type   var mySet   Set of someArray

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Varargs will work too   Stream of T    values  collect Collectors toSet

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Java 8  We have the option of using Stream as well  We can get stream in various ways   Set lt String gt  set   Stream of  A    B    C    D   collect Collectors toCollection HashSet  new    System out println set    String   stringArray     A    B    C    D    Set lt String gt  strSet1   Arrays stream stringArray  collect Collectors toSet     System out println strSet1       if you need HashSet then use below option  Set lt String gt  strSet2   Arrays stream stringArray  collect Collectors toCollection HashSet  new    System out println strSet2     The source code of Collectors toSet   shows that elements are added one by one to a HashSet but specification does not guarantee it will be a HashSet       There are no guarantees on the type  mutability  serializability  or   thread-safety of the Set returned     So it is better to use the later option  The output is    A  B  C  D   A  B  C  D   A  B  C  D   Immutable Set  Java 9   Java 9 introduced Set of static factory method which returns immutable set for the provided elements or the array     SafeVarargs static  lt E gt  Set lt E gt  of  E    elements    Check Immutable Set Static Factory Methods for details   Immutable Set  Java 10   We can also get an immutable set in two ways    Set copyOf Arrays asList array   Arrays stream array  collect Collectors toUnmodifiableList       The method Collectors toUnmodifiableList   internally makes use of Set of introduced in Java 9  Also check this answer of mine for more

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There has been a lot of great answers already  but most of them won t work with array of primitives  like int    long    char    byte    etc    In Java 8 and above  you can box the array with   Integer   boxedArr   Arrays stream arr  boxed   toArray Integer    new     Then convert to set using stream   Stream of boxedArr  collect Collectors toSet

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For anyone solving for Android   Kotlin Collections Solution  The asterisk   is the spread operator  It applies all elements in a collection individually  each passed in order to a vararg method parameter  It is equivalent to   val myArray   arrayOf  data    foo   val mySet   setOf  myArray      Equivalent to val mySet   setOf  data    foo       Multiple spreads   data    foo    bar    data    foo   val mySet   setOf  myArray   bar    myArray    Passing no parameters setOf   results in an empty set   In addition to setOf  you can also use any of these for a specific hash type   hashSetOf   linkedSetOf   mutableSetOf   sortableSetOf     This is how to define the collection item type explicitly   setOf lt String gt    hashSetOf lt MyClass gt

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With Guava you can do   T   array       Set lt T gt  set   Sets newHashSet array

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Set lt T gt  b   new HashSet lt  gt  Arrays asList requiredArray

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Set lt T gt  mySet   new HashSet lt T gt     Collections addAll mySet  myArray     That s Collections addAll java util Collection  T     from JDK 6   Additionally  what if our array is full of primitives   For JDK  lt  8  I would just write the obvious for loop to do the wrap and add-to-set in one pass   For JDK    8  an attractive option is something like   Arrays stream intArray  boxed   collect Collectors toSet

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private Map lt Integer  Set lt Integer gt  gt  nobreaks   new HashMap    nobreaks put 1  new HashSet Arrays asList new int   2  4  5      System out println  expected size is 3     nobreaks get 1  size       the output is  expected size is 3  1   change it to   nobreaks put 1  new HashSet Arrays asList  2  4  5        the output is  expected size is 3  3

[java] How to convert an Array to a Set in Java

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