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fun main(args:Array<String>){

    var arraylist= ArrayList<String>()

    println("First name:"+ arraylist.get(0))
    arraylist.set(0," Laya Hussein")

    println(" all element by object")
    for ( item in arraylist){

    println(" all element by index")
    for( index in 0..arraylist.size-1){

My question why we add -1 for iterating? it is not clicking with me.

The indices of the array are zero based. This means that in arrayOf("A", "B", "C")

A has index 0, B has index 1 and C has index 2. So the last valid index is the array's size - 1 which is 3 - 1 = 2

If you don't want to worry about that you can use indices extension property which is an IntRange of all valid indices.

for(index in arraylist.indices) {

Notice the replacment of get with the operator notation [] which makes the code more concise.

If you don't care for the index, avoid the headache alltogether and use forEach

arraylist.forEach {

How to implement an ArrayList structure in Java, How to implement an ArrayList structure in Java - Tutorial. Lars Vogel (c) 2008, 2019 vogella GmbH. Version 1.2,29.09.2016. The following example is contained in the project called de.vogella.datastructures.list. A List represents a data structure which allows to dynamically add, access and remove objects of the same type. Adding objects to the list is usually done via the add () method. The get (int i) method allows to retrieve the element at position i.

Because if you don't add the -1, it will iterate through 0 to the size of the list. Which means, if we have a list of size 5, it will iterate: 0, 1, 2, 3, 4, 5

And obviously index 5 is not a valid index here, so we need to make sure we don't iterate too far.

How ArrayList Works Internally in Java, space created by the removal of an element has to be filled in the underlying array. ArrayList is the most popular implementation of List in java. ArrayList is very similar to Array but provides the feature of dynamic space allocation when the number of objects in the list grows. In Array, we have to provide the size at the time of initialization but that is not required for ArrayList.

strong textArrays in Kotlin have zero-based index. To iterate through the whole array we need to use indexes from 0 to array.size()-1. Operator .. means including both ranges, so to iterate through the whole array:

for (index in 0..arraylist.size - 1) {
   // ...

We can use function until to avoid using arraylist.size-1, it includes left range but excludes right range:

for (index in 0 until arraylist.size) {
   // ...

Also we can use shorter version of for loop just to iterate through the all elements of array:

for (item in arraylist) {
   // ...

Data Structure, What data structure is used to implement the ArrayList in Java? That is where the resizable-array implementation feature of the ArrayList is covered. If you see the ArrayList internal implementation in Java, everytime add() method is called it is ensured that ArrayList has required capacity. If the capacity is exhausted a new array is created with 50% more capacity than the previous one. All the elements

Data Structures - ArrayList in Java, named words has its underlying array of the size n. ArrayList is a resizable array implementation of the List interface i.e. ArrayList grows dynamically as the elements are added to it. If the size of the current elements (including the new element to be added to the ArrayList) is greater than the maximum size of the array then increase the size of array. But the size of the array can not be increased dynamically.

How to implement ArrayList with Array in Java, ArrayList implementation in Java. We can implement a custom ArrayList using an Array object. The ArrayList is backed by an array to store its elements. The java.util.ArrayList class provides resizable-array and implements the List interface.Following are the important points about ArrayList − It implements all optional list operations and it also permits all elements, includes null. It provides methods to manipulate the size of the array that is used internally to store the list.

Write a program to implement ArrayList., Write a program to implement your own ArrayList class. It should contain add(), get(), remove(), size() methods. Use dynamic array logic. It should increase its  Write a program to implement your own ArrayList class. It should contain add(), get(), remove(), size() methods. Use dynamic array logic. It should increase its size when it reaches threshold.

  • Thank for explaining.
  • This is the more idiomatic solution.
  • Additionally there is for(index in array.indices), array.forEach and array.forEachIndexed