AbstractSet add() method in Java with Example

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

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