Collection add() Method in Java with Examples

29 Nov, 2021
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);    }}
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);    }}
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);        }    }}
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 classesimport java.util.*; // Main class// LinkedListDemoclass 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);        }    }}
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.
solankimayank
surinderdawra388
anikakapoor
varshagumber28
Java - util package
Java-Collections
Java-Functions
Java
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Java-Collections
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