The add(E e) method of AbstractQueue inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions. It returns true upon success and throws an IllegalStateException if no space is currently available.
Syntax:
public boolean add(E e)
Parameters: This method accepts a mandatory parameter e which is the element to be inserted to the queue.
Returns: This method returns true if the element is inserted in the Queue else it returns false.
Exception: This method throws following exceptions:
- IllegalStateException: if the element cannot be added at this time due to capacity restrictions
- NullPointerException: if the specified element is null
- ClassCastException – if the class of the specified element prevents it from being added to this queue
- IllegalArgumentException – if some property of this element prevents it from being added to this queue
Below programs illustrate add() method:
Program 1:
// Java program to illustrate the// AbstractQueue add() methodimport java.util.*;import java.util.concurrent.LinkedBlockingQueue;  public class GFG1 {    public static void main(String[] argv)        throws Exception    {        // Creating object of AbstractQueue<Integer>        AbstractQueue<Integer>            AQ = new LinkedBlockingQueue<Integer>();          // Populating AQ        AQ.add(10);        AQ.add(20);        AQ.add(30);        AQ.add(40);        AQ.add(50);          // print AQ        System.out.println("AbstractQueue contains : " + AQ);    }} |
Output:
AbstractQueue contains : [10, 20, 30, 40, 50]
Program 2: Program for IllegalStateException
// Java program to illustrate the// AbstractQueue add() method// IllegalStateExceptionimport java.util.*;import java.util.concurrent.LinkedBlockingQueue;  public class GFG1 {    public static void main(String[] argv)        throws Exception    {        try {            // Creating object of AbstractQueue<Integer>            AbstractQueue<Integer>                AQ = new LinkedBlockingQueue<Integer>(2);              // Populating AQ            AQ.add(10);            AQ.add(20);            AQ.add(30);            AQ.add(40);            AQ.add(50);              // print AQ            System.out.println("AbstractQueue contains : " + AQ);        }        catch (Exception e) {            System.out.println("exception: " + e);        }    }} |
Output:
exception: java.lang.IllegalStateException: Queue full
Program 3: Program for NullPointerException
// Java program to illustrate the// AbstractQueue add() method// NullPointerExceptionimport java.util.*;import java.util.concurrent.LinkedBlockingQueue;  public class GFG1 {    public static void main(String[] argv)        throws Exception    {        try {            // Creating object of AbstractQueue<Integer>            AbstractQueue<Integer>                AQ = new LinkedBlockingQueue<Integer>();              // Populating AQ            AQ.add(10);            AQ.add(20);            AQ.add(30);            AQ.add(null);            AQ.add(50);              // print AQ            System.out.println("AbstractQueue contains : " + AQ);        }        catch (Exception e) {            System.out.println("exception: " + e);        }    }} |
Output:
exception: java.lang.NullPointerException
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/AbstractQueue.html#add-E-
