Java ArrayList Add() - How to add values to ArrayList?

How to add values to ArrayList?

In this post, we will learn how to add elements to ArrayList using java inbuilt methods. ArrayList class in java has been implemented based on the growable array which will be resized size automatically. Maintains the order of insertion of values added to it and permits adding all kinds of values including primitives, user-defined classes, wrapper classes and null values.

Java ArrayList add methods:

Java ArrayList add method is overloaded and the following are the methods defined in it.

1) public boolean add(E e)
2) public void add(int index, E element)

1) add(E e) method example:

Appends the specified element to the end of this list.

Below are example code snippet for adding.

list.add("Peter");

address.add("Chicago, USA");

ages.add(new Integer(30));

values.add(null);

How to add the values at the end of arraylist?

package blog.java.w3schools.arraylist;

import java.util.ArrayList;

import java.util.List;

public class ArrayListAddExample {
 public static void main(String[] args) {

  List<String> addExample = new ArrayList<String>();

  addExample.add("Jhon Cena");

  addExample.add("Batista");

  addExample.add("Rock");

  System.out.println("Printing values to the arraylist: " + addExample);

  // Adding new values to existing list.

  addExample.add("Undertaker");

  System.out.println("After adding new value: " + addExample);
 }
}

Output:

Printing values to the arraylist: [Jhon Cena, Batista, Rock]

After adding new value: [Jhon Cena, Batista, Rock, Undertaker]

First, observe the list that we added three values to it and printed them. We see them in output as in the insertion order. After that added another value "Undertaker" then see the output. The new value is added at the end of the list.
When you use add method, it always adds it to the end of the element.

2) public void add(int index, E element):

ArrayList has another add method which takes index and value where the index is the position of the new element to be inserted
(Inserts the specified element at the specified position in this list).
It provides flexibility to add the beginning/end/nth position of ArrayList. Index starts from 0 like Array.

Read more Introduction to ArrayList over Arrays.

How to add values to the beginning of the ArrayList?

package blog.java.w3schools.arraylist;

import java.util.ArrayList;

import java.util.List;

public class AddBeginExample {
 public static void main(String[] args) {

  List<Integer> numbers = new ArrayList<Integer>();

  numbers.add(100);

  System.out.println("After adding first value: " + numbers);

  numbers.add(0, 80);

  System.out.println("After adding second value: " + numbers);

  numbers.add(0, 60);

  System.out.println("After adding third value: " + numbers);

  numbers.add(0, 40);

  System.out.println("After adding fourth value: " + numbers);

  numbers.add(0, 20);

  System.out.println("After adding fifth value: " + numbers);

 }

}

Output:

After adding first value: [100]

After adding second value: [80, 100]

After adding third value: [60, 80, 100]

After adding fourth value: [40, 60, 80, 100]

After adding fifth value: [20, 40, 60, 80, 100]

Printed list after adding each value. Passed index 0 to add method. When added second value 80 that value inserted at the first position, values right to it are shifted right by one position.

ArrayList implicitly does convert primitives types to wrapper types.

// Adds value at 2nd position.
numbers.add(2, 60);

// Adds value at last position using another way.
numbers.add(numbers.size()-1, 60);

// Adds after middle value of arraylist.
numbers.add(numbers.size()/2, 60);

Summary:

Java ArrayList Add method is a overloaded method which has two versions. Add(Element e) adds the element at the last of list whereas another add(int index, Element e) inserts value at a specified position. We have discussed about How to append elements at the end of ArrayList in Java? How to add elements at the beginning or nth position.