Java ArrayList add() Usage and Example

Java ArrayList Methods

　The Java ArrayList add() method inserts an element at the specified position in the ArrayList.

Syntax of add() method:

arraylist.add(int index, E element)

add() parameters

The ArrayList add() method can take two parameters:

• index (Optional)- Index of the element to be inserted

• element - Element to be inserted

If no index is passed, the element is appended to the end of the arraylist.

add() return value

• 　If the element is successfully inserted, it returns true.
  

Note:If the index is out of range, the add() method throws an IndexOutOfBoundsException exception.

Example1Insert element using ArrayList add()

import java.util.ArrayList;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Create ArrayList
　　　　　　　　ArrayListprimeNumbers = new ArrayList<>();
　　　　　　　　//Insert element into the arraylist
　　　　　　　　primeNumbers.add(2);
　　　　　　　　primeNumbers.add(3);
　　　　　　　　primeNumbers.add(5);
　　　　　　　　System.out.println("ArrayList: "　+　primeNumbers);
　　　　}
}

Output Result

ArrayList: [2,　3,　5]

In the above example, we created an ArrayList named primeNumbers. Here, the add() method does not have an optional index parameter. Therefore, all elements are inserted at the end of the arraylist.

Example2Insert element at specified position

import java.util.ArrayList;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Create ArrayList
　　　　　　　　ArrayListlanguages = new ArrayList<>();
　　　　　　　　//　Insert element at the end of the arraylist　
　　　　　　　　languages.add("Java");
　　　　　　　　languages.add("Python");
　　　　　　　　languages.add("JavaScript");
　　　　　　　　System.out.println("ArrayList: "　+　languages);
　　　　　　　　//　at Position1Insert Element　
　　　　　　　　languages.add(1,　"C++");
　　　　　　　　System.out.println("Updated ArrayList: ",　+　languages);
　　　　}
}

Output Result

ArrayList:　[Java,　Python,　JavaScript]
Updated ArrayList:　[Java,　C++,　Python,　JavaScript]

In the above example, we use the add() method to insert elements into the arraylist. Note this line,

languages.add(1,　"C++");

　Here, the add() method has an optional index parameter. Therefore, C++at index1insertion.

NoteAs of now, we have only added a single element. However, we can also use the addAll() method to add multiple elements from a collection (array list, set, map, etc.) to an array list. For more information, please visitJava ArrayList addAll().

Java ArrayList Methods