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.
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