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.

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 its is accepting it whether it needs to support null.