How to insert an object in an ArrayList at a specific position

Question

Suppose I have an ArrayList of objects of size n  Now I want to insert an another object at specific position  let s say at index position k  is greater than 0 and less than n  and I want other objects at and after index position k to shift one index position ahead  So is there any way to do this directly in Java  Actually i want to keep the list sorted while adding new object

User · Answer

You must handle ArrayIndexOutOfBounds by yourself when adding to a certain position.

For convenience, you may use this extension function in Kotlin

/**
 * Adds an [element] to index [index] or to the end of the List in case [index] is out of bounds
 */
fun <T> MutableList<T>.insert(index: Int, element: T) {
    if (index <= size) {
        add(index, element)
    } else {
        add(element)
    }
}

User · Answer

Here is the simple arraylist example for insertion at specific index  ArrayList lt Integer gt  str new ArrayList lt Integer gt         str add 0       str add 1       str add 2       str add 3          Result    0  1  2  3      str add 1  11       str add 2  12         Result    0  11  12  1  2  3

User · Answer

Actually the way to do it on your specific question is arrayList add 1  INSERTED ELEMENT    where 1 is the position

User · Answer

Note that when you insert into a List at a position  you are really inserting at a dynamic position within the List s current elements  See here   http   tpcg io 0KmArS  package com tutorialspoint   import java util ArrayList   public class ArrayListDemo      public static void main String   args              create an empty array list with an initial capacity       ArrayList lt Integer gt  arrlist   new ArrayList lt Integer gt  5             use add   method to add elements in the list       arrlist add 15  15         arrlist add 22  22         arrlist add 30  30         arrlist add 40  40             adding element 25 at third position       arrlist add 2  25             let us print all the elements available in list       for  Integer number   arrlist             System out println  Number       number                          javac com tutorialspoint ArrayListDemo java       java -Xmx128M -Xms16M com tutorialspoint ArrayListDemo  Exception in thread  main  java lang IndexOutOfBoundsException  Index  15  Size  0     at java util ArrayList rangeCheckForAdd ArrayList java 661      at java util ArrayList add ArrayList java 473      at com tutorialspoint ArrayListDemo main ArrayListDemo java 12

User · Answer

To insert value into ArrayList at particular index  use         public void add int index  E element    This method will shift the subsequent elements of the list  but you    can not guarantee the List will remain sorted as the new Object you insert may sit on the wrong position according to the sorting order     To replace the element at the specified position  use   public E set int index  E element    This method replaces the element at the specified position in the list with the specified element  and returns the element previously at the specified position

User · Answer

This method Appends the specified element to the end of this list  add E e    append element to the end of the arraylist   This method Inserts the specified element at the specified position in this list  void add int index  E element    inserts element at the given position in the array list   This method Replaces the element at the specified position in this list with the specified element  set int index  E element    Replaces the element at the specified position in this list with the specified element

[java] How to insert an object in an ArrayList at a specific position

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