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: This method returns 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 following exceptions:
- 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
Below examples illustrate the Collection add() method:
Example 1: Using LinkedList Class
// 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: Using ArrayDeque Class
// 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 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
Example 4: To demonstrate NullPointer Exception
// Java code to illustrate boolean add() import java.util.*; public class LinkedListDemo { public static void main(String args[]) { // Creating an empty ArrayList Collection<String> list = new ArrayList<String>(); // Displaying the list System.out.println( "The ArrayList is: " + list); try { // Appending the null to the list list.add( null ); } catch (Exception e) { System.out.println( "Exception: " + e); } } } |
The ArrayList is: []
Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Collection.html#add-E-
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