ArrayList Add method, How to add values to ArrayList in java, Example

Java ArrayList Add method is two overloaded methods. Add(Element e), add(int index, Element e). Example programs to append elements at the end/beginning/nth position.

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

Java ArrayList add methods:

Java ArrayList add method is overloaded and 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, observer 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. New value is added at the end of the list.
When you use add method, it always add 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 index is the position of the new element to be inserted
(Inserts the specified element at the specified position in this list).
It provides felxibility to add the beinging/end/nth position of ArrayList. Index starts from 0 like Array.

Read more Introduction to ArrayList over Arrays.

How to add values to the begining 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 first position, values right to it are shifed right by one position.

ArrayList implicitly does converting 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.