AbstractQueue add() method in Java with examples

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() method
import 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
// IllegalStateException
import 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
// NullPointerException
import 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-