Java Deque addFirst() Method

The addFirst() method of Java Deque Interface is used to insert the specified element at the front of the deque .

Syntax:

Parameter:

The above method consists of only one parameter:

The element 'e' that needs to be added.

Return:

Throw:

IllegalStateException- If the elements cannot be added at the time due to capacity restriction.

ClassCastException- If the class of the specified element avoids it from being added to the deque.

NullPointerException- If the specified element is a null and the deque does not allow the null elements.

IllegalArgumentException- If some of the property of the given element avoids it from being added to the deque.

Example 1

import java.util.ArrayDeque;
import java.util.Deque;
public class JavaDequeaddFirstExample1 {
     public static void main(String[] args) {
		Deque<Integer> deque = new ArrayDeque<>();
		deque.addFirst(44);
		deque.addFirst(33);
		deque.addFirst(22);
		deque.addFirst(11);
    	System.out.println("The elements are adding at the front of the deque : "+deque);   	 
	}
}

Test it Now

Output:

The elements are adding at the front of the deque : [11, 22, 33, 44]

Example 2

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

public class JavaDequeaddFirstExample2 {
   public static void main(String[] args) {
	   Deque<String> deque = new ArrayDeque<>();
		deque.addFirst("FAT");
		deque.addFirst("CAO");
		deque.addFirst("JAVA");
		deque.addFirst("DBMS");
   	System.out.println("The subjects are given as : "+deque); 
     }
}

Output:

The subjects are given as : [DBMS, JAVA, CAO, FAT]

Example 3

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

public class JavaDequeaddFirstExample3 {
   public static void main(String[] args) {
	 System.out.print("Enter the number of times you want to enter the names : ");
	 Scanner scanner = new Scanner(System.in);
	 int n = scanner.nextInt();
	
	 Deque<String> deque = new ArrayDeque<String>();
	 System.out.println("The names are : ");
	 for (int i = 0; i < n; i++) {
	  String name = scanner.next();
	  deque.addFirst(name);
	  }
	 System.out.println("The final deque is : "+deque);
   }
}

Output:

Enter the number of times you want to enter the names : 4
The names are : 
Sham
Ram
Stuti
Ranajna
The final deque is : [Ranajna, Stuti, Ram, Sham]

Next TopicJava Deque

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