Array to Collection Optimized code

Question

Is there a better way of achieving this   public static List lt String gt  toList String   array         List lt String gt  list   new ArrayList array length        for int i 0  i lt array length  i            list add array i         return list      NOTE  Arrays asList a  Returns a fixed-size list backed by the specified array   Changes to the returned list  write through  to the array    I don t want that behavior  I assume that MY function above bypasses that  or am I wrong    So  here we have the alternative method   public static List lt String gt  toList String   array         List lt String gt  list   new ArrayList array length        list addAll Arrays asList array         return list      Just looking at it  I don t believe it s FASTER than the first method

User · Answer

You can use   list addAll Arrays asList array

User · Answer

Another way to do it   Collections addAll collectionInstance array

User · Answer

Based on the reference of  java util Collections addAll Collection lt   super String gt  c  String    elements  its implementation is similar to your first method  it says     Adds all of the specified elements to the specified collection  Elements to be added may be specified individually or as an array  The behavior of this convenience method is identical to that of c addAll Arrays asList elements    but this method is likely to run significantly faster under most implementations    Its implementation in jdk is  jdk7   public static  lt T gt  boolean addAll Collection lt   super T gt  c  T    elements        boolean result   false      for  T element   elements          result    c add element       return result      So among your samples the better approach must be Collections addAll list  array    Since Java 8  we can use Stream api which may perform better  Eg -   String   array     item1    item2    item3     Stream lt String gt  stream   Stream of array      if the array is extremely large  stream   stream parallel     final List lt String gt  list   stream collect Collectors toList       If the array is very large we can do it as a batch operation in parallel using parallel stream  stream   stream parallel    that will utilize all CPUs to finish the task quickly  If the array length is very small parallel stream will take more time than sequential stream

User · Answer

Arrays asList array    Arrays uses new ArrayList array   But this is not the java util ArrayList  It s very similar though  Note that this constructor takes the array and places it as the backing array of the list  So it is O 1    In case you already have the list created  Collections addAll list  array   but that s less efficient   Update  Thus your Collections addAll list  array  becomes a good option  A wrapper of it is guava s Lists newArrayList array

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You can try something like this   List lt String gt  list   new ArrayList lt String gt  Arrays asList array         public ArrayList Collection c       Constructs a list containing the   elements of the specified collection    in the order they are returned by the   collection s iterator  The ArrayList   instance has an initial capacity of   110  the size of the specified   collection    Taken from here

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Yes  there is  You can use the Arrays class from the java util   package  Then it s actually just one line of code   List lt String gt  list   Arrays asList array

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What about    List myList   new ArrayList     String   myStringArray   new String     Java    is    Cool      Collections addAll myList  myStringArray

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What do you mean by better way   more readable   List lt String gt  list   new ArrayList lt String gt  Arrays asList array      less memory consumption  and maybe faster  but definitely not thread safe    public static List lt String gt  toList String   array        if  array  null           return new ArrayList 0         else          int size   array length         List lt String gt  list   new ArrayList size          for int i   0  i  lt  size  i                list add array i                    return list            Btw  here is a bug in your first example   array length will raise a null pointer exception if array is null  so the check if  array  null  must be done first

User · Answer

Arrays asList array         Example     List lt String gt  stooges   Arrays asList  Larry    Moe    Curly      See Arrays asList class documentation

User · Answer

Have you checked Arrays asList    see API

[java] Array to Collection: Optimized code

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