From Arraylist to Array

Question

I want to know if it is safe advisable to convert from ArrayList to Array  I have a text file with each line a string   1236 1233 4566 4568        I want to read them into array list and then i convert it to Array  Is it advisable legal to do that   thanks

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ArrayList lt String gt  a   new ArrayList lt String gt     a add   test      SuppressWarnings   unused   Object   array   a toArray      It depends on what you want to achieve if you need to manipulate the array later it would cost more effort than keeping the string in the ArrayList  You have also random access with an ArrayList by list get  index

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One approach would be to add the Second for Loop where the printing is being done  inside the first for loop  Like this   static String   SENTENCE    public static void main String   args  throws Exception      Scanner sentence   new Scanner new File  assets blah txt        ArrayList lt String gt  sentenceList   new ArrayList lt String gt         while  sentence hasNextLine                sentenceList add sentence nextLine              sentence close        String   sentenceArray   sentenceList toArray new String sentenceList size           System out println sentenceArray length      for  int r 0 r lt sentenceArray length r                SENTENCE   sentenceArray r  split     lt          s       split sentences and store in array          for  int i 0 i lt SENTENCE length i                        System out println  Sentence      i 1           SENTENCE i

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This is the best way  IMHO    List lt String gt  myArrayList   new ArrayList lt String gt             String   myArray   myArrayList toArray new String myArrayList size        This code works also   String   myArray   myArrayList toArray new String 0      But it less effective  the string array is created twice  first time zero-length array is created  then the real-size array is created  filled and returned  So  if since you know the needed size  from list size    you should create array that is big enough to put all elements  In this case it is not re-allocated

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There are two styles to convert a collection to an array  either using a pre-sized array  like c toArray new String c size      or using an empty array  like c toArray new String 0     In older Java versions using pre-sized array was recommended  as the reflection call which is necessary to create an array of proper size was quite slow  However since late updates of OpenJDK 6 this call was intrinsified  making the performance of the empty array version the same and sometimes even better  compared to the pre-sized version  Also passing pre-sized array is dangerous for a concurrent or synchronized collection as a data race is possible between the size and toArray call which may result in extra nulls at the end of the array  if the collection was concurrently shrunk during the operation  You can follow the uniform style  either using an empty array  which is recommended in modern Java  or using a pre-sized array  which might be faster in older Java versions or non-HotSpot based JVMs

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assuming v is a ArrayList   String   x    String    v toArray new String 0

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ArrayList lt String gt  myArrayList   new ArrayList lt String gt         String   myArray   myArrayList toArray new String 0      Whether it s a  good idea  would really be dependent on your use case

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This is the recommended usage for newer Java    Java 6   String   myArray   myArrayList toArray new String 0         In older Java versions using pre-sized array was recommended  as the   reflection call which is necessary to create an array of proper size   was quite slow  However since late updates of OpenJDK 6 this call was   intrinsified  making the performance of the empty array version the   same and sometimes even better  compared to the pre-sized version    Also passing pre-sized array is dangerous for a concurrent or   synchronized collection as a data race is possible between the size   and toArray call which may result in extra nulls at the end of the   array  if the collection was concurrently shrunk during the operation    This inspection allows to follow the uniform style  either using an   empty array  which is recommended in modern Java  or using a pre-sized   array  which might be faster in older Java versions or non-HotSpot   based JVMs

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Yes it is safe to convert an ArrayList to an Array  Whether it is a good idea depends on your intended use  Do you need the operations that ArrayList provides  If so  keep it an ArrayList  Else convert away   ArrayList lt Integer gt  foo   new ArrayList lt Integer gt     foo add 1   foo add 1   foo add 2   foo add 3   foo add 5   Integer   bar   foo toArray new Integer foo size      System out println  bar length       bar length     outputs  bar length   5

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The Collection interface includes the toArray   method to convert a new collection into an array  There are two forms of this method  The no argument version will return the elements of the collection in an Object array  public Object    toArray    The returned array cannot cast to any other data type  This is the simplest version  The second version requires you to pass in the data type of the array you   d like to return  public Object     toArray Object type         public static void main String   args                 List lt String gt  l new ArrayList lt String gt                  l add  A                 l add  B                 l add  C                 Object arr   l toArray                 for Object a arr                                   String str  String a                    System out println str                                for reference  refer this link http   techno-terminal blogspot in 2015 11 how-to-obtain-array-from-arraylist html

[java] From Arraylist to Array

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