Collection add() Method in Java with Examples
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.
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
- 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
The list is: [Geeks, for, Geeks] The new List is: [Geeks, for, Geeks, Last, Element]
Example 2: ArrayDeque Class
ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Example 3: Using ArrayList Class
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:
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 its is accepting it whether it needs to support null.