The java.util.ArrayDeque.pollFirst() method in Java is used to retrieve or fetch and remove the first element of the Deque. The peekFirst() method only retrieved the first element but the pollFirst() also removes the element along with the retrieval. It returns NULL if the deque is empty.
Syntax:
Array_Deque.pollFirst()
Parameters: The method does not take any parameter.
Return Value: The method removes the first element of the Deque and returns the same. It returns NULL if the deque is empty.
Below programs illustrate the Java.util.ArrayDeque.pollFirst() method:
Program 1:
// Java code to illustrate pollFirst() import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<String> de_que = new ArrayDeque<String>();
// Use add() method to add elements into the Deque
de_que.add( "Welcome" );
de_que.add( "To" );
de_que.add( "Geeks" );
de_que.add( "4" );
de_que.add( "Geeks" );
// Displaying the ArrayDeque
System.out.println( "ArrayDeque: " + de_que);
// Displaying the first element
System.out.println( "The element at head is: " +
de_que.pollFirst());
// Displaying the final ArrayDeque
System.out.println( "ArrayDeque after operation: " + de_que);
}
} |
ArrayDeque: [Welcome, To, Geeks, 4, Geeks] The element at head is: Welcome ArrayDeque after operation: [To, Geeks, 4, Geeks]
Program 2:
// Java code to illustrate pollFirst() import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<Integer> de_que = new ArrayDeque<Integer>();
// Use add() method to add elements into the Deque
de_que.add( 10 );
de_que.add( 15 );
de_que.add( 30 );
de_que.add( 20 );
de_que.add( 5 );
// Displaying the ArrayDeque
System.out.println( "ArrayDeque: " + de_que);
// Displaying the first element
System.out.println( "The element at head is: " +
de_que.pollFirst());
// Displaying the final ArrayDeque
System.out.println( "ArrayDeque after operation: " + de_que);
}
} |
ArrayDeque: [10, 15, 30, 20, 5] The element at head is: 10 ArrayDeque after operation: [15, 30, 20, 5]
Program 3: For an empty deque:
// Java code to illustrate pollFirst() import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<Integer> de_que = new ArrayDeque<Integer>();
// Displaying the ArrayDeque
System.out.println( "ArrayDeque: " + de_que);
// Displaying the first
System.out.println( "The element at head is: " +
de_que.pollFirst());
}
} |
ArrayDeque: [] The element at head is: null