Collection add() Method in Java with Examples
Last Updated : 07 Oct, 2022
The add(E element) of java.util.Collection interface is used to add the element 'element' to this collection. This method returns a boolean value depicting the successfulness of the operation. If the element was added, it returns true, else it returns false.
Syntax:
Collection.add(E element)
Parameters: This method accepts a mandatory parameter element of type E which is to be added to this collection.
Return Value: A boolean value depicting the successfulness of the operation. If the element was added, it returns true, else it returns false.
Exceptions: This method throws 5 following exceptions listed below as follows:
- UnsupportedOperationException: if the add operation is not supported by this collection
- ClassCastException: if the class of the specified element prevents it from being added to this collection
- NullPointerException: if the specified element is null and this collection does not permit null elements
- IllegalArgumentException: if some property of the element prevents it from being added to this collection
- IllegalStateException: if the element cannot be added at this time due to insertion restrictions
Now we will be implementing this method over different classes as it is a very important and essential method when it comes downs to java programming so here we will be stressing over each class as follows:
- LinkedList class
- ArrayDeque
- ArrayList class
- NullPointerException is Thrown
Let us implement add() method in all 4 above listed cases via clean java examples as follows:
Example 1: LinkedList Class
Java // Java code to illustrate boolean add() method import java.io.*; import java.util.*; public class GFG { public static void main(String args[]) { // creating an empty LinkedList Collection<String> list = new LinkedList<String>(); // use add() method to add elements in the list list.add("Geeks"); list.add("for"); list.add("Geeks"); // Output the present list System.out.println("The list is: " + list); // Adding new elements to the end list.add("Last"); list.add("Element"); // printing the new list System.out.println("The new List is: " + list); } } Output: The list is: [Geeks, for, Geeks] The new List is: [Geeks, for, Geeks, Last, Element]
Example 2: ArrayDeque Class
Java // Java code to illustrate add() method import java.util.*; public class ArrayDequeDemo { public static void main(String args[]) { // Creating an empty ArrayDeque Collection<String> de_que = new ArrayDeque<String>(); // Use add() method to add elements into the Deque de_que.add("Welcome"); de_que.add("To"); de_que.add("Geeks"); de_que.add("4"); de_que.add("Geeks"); // Displaying the ArrayDeque System.out.println("ArrayDeque: " + de_que); } } Output: ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Example 3: Using ArrayList Class
Java // Java code to illustrate add() method import java.io.*; import java.util.*; public class ArrayListDemo { public static void main(String[] args) { // create an empty array list with an initial capacity Collection<Integer> arrlist = new ArrayList<Integer>(5); // use add() method to add elements in the list arrlist.add(15); arrlist.add(20); arrlist.add(25); // prints all the elements available in list for (Integer number : arrlist) { System.out.println("Number = " + number); } } } Output: Number = 15 Number = 20 Number = 25
Geeks do keep an bound over special case where NullPointer Exception will be thrown as show in below example as follows:
Example 4:
Java // Java code to illustrate boolean add() // Where NullPointerException is Thrown // Importing required utility classes import java.util.*; // Main class // LinkedListDemo class GFG { // Main driver method public static void main(String args[]) { // Creating an empty ArrayList of string type Collection<String> list = new ArrayList<String>(); // Printing and displaying the Arraylist System.out.println("The ArrayList is: " + list); // Note: Here by now we have not added any element/s // Try block to check for exceptions try { // Appending the null to the list // using add() method list.add(null); } // Catch block to handle exceptions catch (Exception e) { // Display message when exceptions occurs System.out.println("Exception: " + e); } } } Output: The ArrayList is: []
Output explanation: Here we need to pick it up as we will only receive a List. So it is good practice to document for add() method either it is accepting it whether it needs to support null.