The add(E) method of AbstractSet Class appends the specified element to the end of this AbstractSet.
Syntax:
boolean add(E element)
Parameters: This function accepts a single parameter element as shown in the above syntax. The element specified by this parameter is appended to end of the AbstractSet.
Return Value: This method returns True after successful execution, else False.
Exception: This method throws:
- 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 program illustrates the working of java.util.AbstractSet.add(E element) method:
Example 1:
// Java code to illustrate boolean add(E element)import java.util.*;  public class AbstractSetDemo {    public static void main(String args[])    {          // Creating an empty AbstractSet        AbstractSet<String> set            = new TreeSet<String>();          // Use add() method        // to add elements in the AbstractSet        set.add("Geeks");        set.add("for");        set.add("Geeks");        set.add("10");        set.add("20");          // Output the present AbstractSet        System.out.println("The AbstractSet is: "                           + set);          // Adding new elements to the end        set.add("Last");        set.add("Element");          // Printing the new AbstractSet        System.out.println("The new AbstractSet is: "                           + set);    }} |
Output:
The AbstractSet is: [10, 20, Geeks, for] The new AbstractSet is: [10, 20, Element, Geeks, Last, for]
Example 2: To demonstrate NullPointerException
// Java code to illustrate// boolean add(E element)  import java.util.*;  public class AbstractSetDemo {    public static void main(String args[])    {          // Creating an empty AbstractSet        AbstractSet<Integer> set            = new TreeSet<Integer>();          // Use add() method        // to add elements in the AbstractSet        set.add(10);        set.add(20);        set.add(30);        set.add(40);        set.add(50);          // Output the present AbstractSet        System.out.println("The AbstractSet is: "                           + set);          System.out.println("Trying to add null");          try {            // Adding null            set.add(null);        }        catch (Exception e) {            System.out.println(e);        }    }} |
Output:
The AbstractSet is: [10, 20, 30, 40, 50] Trying to add null java.lang.NullPointerException
