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 illustrate add() method of PriorityBlockingQueue:

Example 1:

// 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 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-

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