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ConcurrentLinkedDeque removeFirstOccurrence() method in Java

  • Last Updated : 21 Nov, 2019

The java.util.concurrent.ConcurrentLinkedDeque.removeFirstOccurrence() method is an in-built method in Java which accepts a parameter and removes the first appearance of that element in the deque. Thus, in case the element is not present in the deque, it remains unchanged.

Syntax:

public boolean removeFirstOccurrence(Object o)

Parameters: The function accepts an object elem as parameter which denotes the object whose first appearance from the deque is to be removed.

Return Value: The function returns true if elem is present in th edeque and returns false otherwise.

Exception: The function throws NullPointerException if the specified element passed as parameter to the function is null.



Below programs illustrate the use of removeFirstOccurrence() method :

Program 1:




/* Java program to demonstrate 
   removeFirstOccurrence() method
   of ConcurrentLinkedDeque   */
  
import java.util.concurrent.*;
  
class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<String> cld = new ConcurrentLinkedDeque<String>();
  
        cld.addFirst("GFG");
        cld.addFirst("Geeks");
        cld.addFirst("Gfg");
        cld.addFirst("gfg");
        cld.addFirst("Geeks");
  
        // Displaying the existing LinkedDeque
        System.out.println("Elements in "
                           + "the LinkedDeque: " + cld);
  
        // Remove first occurrence of  element
        cld.removeFirstOccurrence("Geeks");
  
        // Displaying the modified LinkedDeque
        System.out.println("Elements in "
                           + "the LinkedDeque: " + cld);
    }
}
Output:
Elements in the LinkedDeque: [Geeks, gfg, Gfg, Geeks, GFG]
Elements in the LinkedDeque: [gfg, Gfg, Geeks, GFG]

Program 2:




/* Java program to demonstrate 
   removeFirstOccurrence() method
   of ConcurrentLinkedDeque   */
  
import java.util.concurrent.*;
  
class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<Integer> cld = new ConcurrentLinkedDeque<Integer>();
  
        cld.addFirst(12);
        cld.addFirst(280);
        cld.addFirst(1008);
        cld.addFirst(1050);
        cld.addFirst(379);
  
        // Displaying the existing LinkedDeque
        System.out.println("Elements in "
                           + "the LinkedDeque: " + cld);
        try {
            // Remove first occurrence of  element
            cld.removeFirstOccurrence(null);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}
Output:
Elements in the LinkedDeque: [379, 1050, 1008, 280, 12]
java.lang.NullPointerException

Reference:https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedDeque.html#removeFirstOccurrence()

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