PriorityBlockingQueue add() Method in Java

The add(E e) method of PriorityBlockingQueue inserts the element passed as a parameter to the method at the tail of this PriorityBlockingQueue. This method returns true if the adding of the element is successful. Else it returns false. 

Syntax:

public boolean add(E e)

Parameter: This method takes a mandatory parameter e which is the element to be inserted in PriorityBlockingQueue. 

Returns: This method returns a boolean response. It returns true if the adding of the element is successful, else it returns false. 

Exception: This method throws following exceptions:

• ClassCastException: if the element passed as parameter cannot be compared to the element contained by queue to keep priority queue’s ordering.
• NullPointerException: if the element passed as parameter is null.

Below program illustrate  add() method of PriorityBlockingQueue: 

Example 1:

Java

// Java Program to Demonstrate add(E e) method
// of PriorityBlockingQueue.

import java.util.concurrent.PriorityBlockingQueue;

public class GFG {

    public static void main(String[] args)
    {
        // define capacity of PriorityBlockingQueue
        int capacity = 15;

        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioBlockingQueue
            = new PriorityBlockingQueue<Integer>(capacity);

        // add  numbers
        PrioBlockingQueue.add(526734);
        PrioBlockingQueue.add(84879456);
        PrioBlockingQueue.add(4586415);

        // print queue after add operation
        System.out.println("After Adding Some Numbers");
        System.out.println("PriorityBlockingQueue:"
                           + PrioBlockingQueue);

        // add more numbers
        PrioBlockingQueue.add(156116);
        PrioBlockingQueue.add(61651191);

        // print queue after add operation
        System.out.println("\nAfter adding Some More Numbers");
        System.out.println("PriorityBlockingQueue:"
                           + PrioBlockingQueue);
    }
}

Output:

After Adding Some Numbers
PriorityBlockingQueue:[526734, 84879456, 4586415]

After adding Some More Numbers
PriorityBlockingQueue:[156116, 526734, 4586415, 84879456, 61651191]

Example 2: To demonstrate NullPointerException thrown by add() method. 

Java

// Java Program to Demonstrate Exception
// thrown by add(E e) method
// of PriorityBlockingQueue.

import java.util.concurrent.PriorityBlockingQueue;

public class GFG {

    public static void main(String[] args)
    {
        // define capacity of PriorityBlockingQueue
        int capacity = 15;

        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioBlockingQueue
            = new PriorityBlockingQueue<Integer>(capacity);

        // add numbers
        PrioBlockingQueue.add(526734);
        PrioBlockingQueue.add(84879456);
        PrioBlockingQueue.add(4586415);
        try {
            // try to add null to PrioBlockingQueue
            PrioBlockingQueue.add(null);

            // print PrioBlockingQueue after add operation
            System.out.println("PriorityBlockingQueue:"
                               + PrioBlockingQueue);
        }
        catch (Exception e) {
            System.out.println("Exception when adding null: "
                               + e);
        }
    }
}

Output:

Exception when adding null: java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#add-E-