ArrayList class in JAVA

We have already seen that arrays are of a fixed length and after they are created, they cannot grow or shrink. This meant the the programmer must know in advance about the size requirement of an array.

ArrayList like arrays also allow object storage, but unlike array, the arrayList are created with an initial size, the arrayList collection is automatically enlarged when object are added and it automatically get shrunk when objects are removed from the arrayList.

There is a class ArrayList to which is in java.util.* package. You always work with ArrayList Object which you pass it to it as:

ArrayList<Integer> // Use class names as Integer, remember you cannot use primitive data type as int

ArrayList<String> names = new ArrayList<>();

Syntax:

Declare ArrayList<>

ArrayList<String> names = new ArrayList<>();

Adding items to ArrayList<>

The following statements will add items in sequence to ArrayList

names.add(“Abhay”); //this is same as name at position ‘0’
names.add(“Balwan”); //position 1
names.add(“Chetan”); // will go to position 2
names.add(“Dayanand”); //position 3

names.add(“Exta”); //position 4

Adding item at specific position

Inserting values at a specific position, but move any item over their at that index down the list

names.add(3,“Chotu“);   //This will insert object Chotu at position 3 and shift  exisiting value at that index  down, So, Dayanand will take position at index  4 and Ekta will go to position 5 in ArrayList<>

To set a value to different one

To set a value at a position to different

names.set(3,“Vikas“); // This will replace Chotu with Vikas at position 3. Chotu will not now existing

Removing an item from the List

names.remove(index 2); // This will totally remove the position 2 values and shrink the arrayList<> upwards

Finding the size of ArrayList<>

Size of ArraList<> is given by object.size() will return exact values in the ArrayList<>

Print the values in the ArrayList<>

System.out.println(names.get(i)

Example:

package com.example;
import java.util.ArrayList;
public class arrays

{

public static void main(String[] args)

{

ArrayList<String> names = new ArrayList<>();
names.add(“Abhay”); //this is same as name at position ‘0’
names.add(“Balwan”); //position 1
names.add(“Chetan”); // will go to position 2
names.add(“Dayanand”); //position 3
names.add(4, “Ekta”);
names.set(2, “Chota Chetan”);
for (int i = 0; i < names.size(); i++)
{

System.out.println(names.get(i));

}

}

}

Run the program and you get the following output

Abhay

Balwan

Chota Chetan

Dayanand

Ekta

Process finished with exit code 0