Removing an element from an Array Java

Question

Is there any fast  and nice looking  way to remove an element from an array in Java

User · Answer

Use an ArrayList   alist remove 1     removes the element at position 1

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okay  thx a lot now i use sth like this   public static String   removeElements String   input  String deleteMe        if  input    null            List lt String gt  list   new ArrayList lt String gt  Arrays asList input            for  int i   0  i  lt  list size    i                  if  list get i  equals deleteMe                     list remove i                                   return list toArray new String 0          else           return new String 0

User · Answer

Sure  create another array

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You can t remove an element from the basic Java array  Take a look at various Collections and ArrayList instead

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I think the question was asking for a solution without the use of the Collections API  One uses arrays either for low level details  where performance matters  or for a loosely coupled SOA integration  In the later  it is OK to convert them to Collections and pass them to the business logic as that   For the low level performance stuff  it is usually already obfuscated by the quick-and-dirty imperative state-mingling by for loops  etc  In that case converting back and forth between Collections and arrays is cumbersome  unreadable  and even resource intensive   By the way  TopCoder  anyone  Always those array parameters  So be prepared to be able to handle them when in the Arena   Below is my interpretation of the problem  and a solution  It is different in functionality from both of the one given by Bill K and jelovirt  Also  it handles gracefully the case  when the element is not in the array   Hope that helps   public char   remove char   symbols  char c        for  int i   0  i  lt  symbols length  i                  if  symbols i     c                        char   copy   new char symbols length-1               System arraycopy symbols  0  copy  0  i               System arraycopy symbols  i 1  copy  i  symbols length-i-1               return copy                      return symbols

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I hope you use the java collection   java commons collections   With an java util ArrayList you can do things like the following    yourArrayList remove someObject    yourArrayList add someObject

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Swap the item to be removed with the last item  if resizing the array down is not an interest

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The best choice would be to use a collection  but if that is out for some reason  use arraycopy  You can use it to copy from and to the same array at a slightly different offset   For example   public void removeElement Object   arr  int removedIdx        System arraycopy arr  removedIdx   1  arr  removedIdx  arr length - 1 - removedIdx         Edit in response to comment   It s not another good way  it s really the only acceptable way--any tools that allow this functionality  like Java ArrayList or the apache utils  will use this method under the covers   Also  you REALLY should be using ArrayList  or linked list if you delete from the middle a lot  so this shouldn t even be an issue unless you are doing it as homework   To allocate a collection  creates a new array   then delete an element  which the collection will do using arraycopy  then call toArray on it  creates a SECOND new array  for every delete brings us to the point where it s not an optimizing issue  it s criminally bad programming   Suppose you had an array taking up  say  100mb of ram  Now  you want to iterate over it and delete 20 elements   Give it a try       I know you ASSUME that it s not going to be that big  or that if you were deleting that many at once you d code it differently  but I ve fixed an awful lot of code where someone made assumptions like that

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You could use the ArrayUtils API to remove it in a  nice looking way   It implements many operations  remove  find  add  contains etc  on Arrays  Take a look  It has made my life simpler

User · Answer

Copy your original array into another array  without the element to be removed   A simplier way to do that is to use a List  Set    and use the remove   method

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Some more pre-conditions are needed for the ones written by Bill K and dadinn  Object   newArray   new Object src length - 1   if  i  gt  0       System arraycopy src  0  newArray  0  i      if  newArray length  gt  i       System arraycopy src  i   1  newArray  i  newArray length - i      return newArray

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Nice looking solution would be to use a List instead of array in the first place   List remove index    If you have to use arrays  two calls to System arraycopy will most likely be the fastest   Foo   result   new Foo source length - 1   System arraycopy source  0  result  0  index   if  source length    index        System arraycopy source  index   1  result  index  source length - index - 1        Arrays asList is also a good candidate for working with arrays  but it doesn t seem to support remove

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You could use commons lang s ArrayUtils   array   ArrayUtils removeElement array  element    commons apache org library Javadocs

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You can not change the length of an array  but you can change the values the index holds by copying new values and store them to a existing index number  1 mike   2 jeff    10   george 11 goes to 1 overwriting mike    Object   array   new Object 10   int count   -1   public void myFunction String string        count        if count    array length             count   0      overwrite first           array count    string

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Your question isn t very clear  From your own answer  I can tell better what you are trying to do   public static String   removeElements String   input  String deleteMe        List result   new LinkedList         for String item   input          if  deleteMe equals item               result add item        return result toArray input       NB  This is untested  Error checking is left as an exercise to the reader  I d throw IllegalArgumentException if either input or deleteMe is null  an empty list on null list input doesn t make sense  Removing null Strings from the array might make sense  but I ll leave that as an exercise too  currently  it will throw an NPE when it tries to call equals on deleteMe if deleteMe is null    Choices I made here   I used a LinkedList  Iteration should be just as fast  and you avoid any resizes  or allocating too big of a list if you end up deleting lots of elements  You could use an ArrayList  and set the initial size to the length of input  It likely wouldn t make much of a difference

[java] Removing an element from an Array (Java)

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