AbstractSet add() method in Java with Example

Last Updated : 24 Dec, 2018
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 
// 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 
// 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
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