Delete item from array and shrink array

Question

How can I delete an item from an array  and then resize the array to the smaller size  Likewise  how can I increase the capacity if I need to add another item

User · Answer

Since an array has a fixed size that is allocated when created, your only option is to create a new array without the element you want to remove.

If the element you want to remove is the last array item, this becomes easy to implement using Arrays.copy:

int a[] = { 1, 2, 3};
a = Arrays.copyOf(a, 2);

After running the above code, a will now point to a new array containing only 1, 2.

Otherwise if the element you want to delete is not the last one, you need to create a new array at size-1 and copy all the items to it except the one you want to delete.

The approach above is not efficient. If you need to manage a mutable list of items in memory, better use a List. Specifically LinkedList will remove an item from the list in O(1) (fastest theoretically possible).

User · Answer

The size of a Java array is fixed when you allocate it  and cannot be changed    If you want to  grow  or  shrink  an existing array  you have to allocate a new array of the appropriate size and copy the array elements  e g  using System arraycopy      or Arrays copyOf        A copy loop works as well  though it looks a bit clunky     IMO    If you want to  delete  an item or items from an array  in the true sense     not just replacing them with null   you need to allocate a new smaller array and copy across the elements you want to retain  Finally  you can  erase  an element in an array of a reference type by assigning null to it   But this introduces new problems    If you were using null elements to mean something  you can t do this  All of the code that uses the array now has to deal with the possibility of a null element in the appropriate fashion   More complexity and potential for bugs1     There are alternatives in the form of 3rd-party libraries  e g  Apache Commons ArrayUtils   but you may want to consider whether it is worth adding a library dependency just for the sake of a method that you could implement yourself with 5-10 lines of code     It is better  i e  simpler     and in many cases  more efficient2  to use a List class instead of an array   This will take care of  at least  growing the backing storage   And there are operations that take care of inserting and deleting elements anywhere in the list   For instance  the ArrayList class uses an array as backing  and automatically grows the array as required   It does not automatically reduce the size of the backing array  but you can tell it to do this using the trimToSize   method  e g   ArrayList l       l remove 21   l trimToSize        Only do this if you really have to      1 - But note that the explicit if  a e     null  checks themselves are likely to be  free   since they can be combined with the implicit null check that happens when you dereference the value of a e     2 - I say it is  more efficient in many cases  because ArrayList uses a simple  double the size  strategy when it needs to grow the backing array   This means that if grow the list by repeatedly appending to it  each element will be copied on average one extra time   By contrast  if you did this with an array you would end up copying each array element close to N 2 times on average

User · Answer

No use of any pre defined function as well as efficient  ---     public static void Delete int d   int   array                Scanner in   new Scanner  System in        int i   size   array length       System out println  ENTER THE VALUE TO DELETE            d   in nextInt             for   i 0 i lt  size i                              if  array i     d                                                          int   arr3  new int size-1                               int   arr4   new int i                               int   arr5   new int size-i-1                                        for  int a  0  a lt i a                                                                                  arr4 a  array a                                           arr3 a    arr4 a                                                                              for  int a  i  a lt size-1 a                                                                                    arr5 a-i    array a 1                                            arr3 a    arr5 a-i                                                             System out println Arrays toString arr3                                               else System out println

User · Answer

Arrays are fixed in size  you cannot resize them after creating them  You can remove an existing item by setting it to null   objects 4    null    But you won t be able to delete that entire slot off the array and reduce its size by 1   If you need a dynamically-sized array  you can use an ArrayList  With it  you can add   and remove   objects  and it will grow and shrink as needed

User · Answer

without using the System arraycopy method you can delete an element from an array with the following       int i   0      int x   0      while i  lt  oldArray length           if oldArray i     3 i             intArray x    oldArray i           i            x            where 3 is the value you want to remove

User · Answer

Using ArrayUtils removeElement Object   Object  from org apache commons lang is by far the easiest way to do this   int   numbers    1 2 3 4 5 6 7     removing number 1 numbers   int   ArrayUtils removeElement numbers  1

User · Answer

You can always expand an array just by increment the size of it while creating an array or you can also change the size after creating  but to shrink or delete elements  The alternate solution without creating a new array  possibly is   package sample   public class Delete       int i      int h 0      int n 10      int   a      public Delete             a   new int 10       a 0  -1       a 1  -1       a 2  -1      a 3  10      a 4  20      a 5  30      a 6  40      a 7  50      a 8  60      a 9  70            public void shrinkArray             for i 0 i lt n i                                  if a i   -1                      h                    else                      break                            while h gt 0                                        for i h i lt n i                                                  a i-1  a i                                             h--                      n--                                System out println n             public void display                 for i 0 i lt n i                          System out println a i                         public static void main String   args               TODO Auto-generated method stub         Delete obj   new Delete            obj shrinkArray            obj display                Please comment for any mistakes

User · Answer

object   newarray   new object oldarray Length-1    for int x 0  x  lt  array Length  x        if   array x     value of array to delete        if   x    array index to delete             newarray x    oldarray x            There is no way to downsize an array after it is created  but you can copy the contents to another array of a lesser size

User · Answer

I have created this function  or class  Im kinda new but my friend needed this also so I created this   public String   name int index  String   z        if index  gt  z length           return z        else           String   returnThis   new String z length - 1           int newIndex   0          for int i   0  i  lt  z length  i                 if i    index                   returnThis newIndex    z i                   newIndex                                    return returnThis             Since its pretty revelant  I thought I would post it here

User · Answer

You can t resize the array  per se  but you can create a new array and efficiently copy the elements from the old array to the new array using some utility function like this   public static int   removeElement int   original  int element       int   n   new int original length - 1       System arraycopy original  0  n  0  element        System arraycopy original  element 1  n  element  original length - element-1       return n      A better approach  however  would be to use an ArrayList  or similar List structure  to store your data and then use its methods to remove elements as needed

[java] Delete item from array and shrink array

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