Java Deque Example

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Deque (Doubly ended queue) is a data structure that allows you to insert and remove elements from both the ends. 

The Deque interface was introduced in Java 6 in java.util.collection package. 

Learn and master Java Collections Framework at Learn Java Collections Framework

The Deque interface extends the Queue interface and all methods provided by Queue are also available in the Deque interface.

Check out Java Queue Interface Example Tutorial

The Deque interface defines methods to access the elements at both ends of the Deque instance. Methods are provided to insert, remove, and examine the elements.

There are three concrete implementations of the Deque interface: LinkedList, ArrayDeque, and LinkedBlockingDeque.

Deque interface methods

The below diagram shows a list of APIs/Methods that the Deque interface provides.

Deque interface Hierarchy Diagram

ArrayDeque implementation of Deque Interface Examples

Java ArrayDeque Example

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

public class ArrayDequeExample {
    public static void main(String[] args) {
     // Creating Deque and adding elements
     Deque<String> deque = new ArrayDeque<String>();
     deque.add("element1");
     deque.add("element2");
     deque.add("element3");
     // Traversing elements
     for (String str : deque) {
        System.out.println(str);
     }
   }
}

Output:

element1
element2
element3

Java ArrayDeque Example: offerFirst() and pollLast()

package com.javaguides.collections.queueexamples;

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

public class DequeExample {
    public static void main(String[] args) {
         Deque<String> deque = new ArrayDeque<String>();
         deque.offer("element1");
         deque.offer("element2");
         deque.add("element3");
         deque.offerFirst("element4");
         System.out.println("After offerFirst Traversal...");
         for (String s : deque) {
             System.out.println(s);
         }
         // deque.poll();
         // deque.pollFirst();//it is same as poll()
         deque.pollLast();
         System.out.println("After pollLast() Traversal...");
         for (String s : deque) {
             System.out.println(s);
         }
    }
}

Output:

After offerFirst Traversal...
element4
element1
element2
element3
After pollLast() Traversal...
element4
element1
element2

Java ArrayDeque Example: Book Class

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

class Book {
    int id;
    String name, author, publisher;
    int quantity;

    public Book(int id, String name, String author, String publisher, int quantity) {
         this.id = id;
         this.name = name;
         this.author = author;
         this.publisher = publisher;
         this.quantity = quantity;
     }
}

public class ArrayDequeExample1 {
     public static void main(String[] args) {
         Deque<Book> set = new ArrayDeque<Book>();
         // Creating Books
         Book b1 = new Book(101, "Let us C", "Yashwant Kanetkar", "BPB", 8);
         Book b2 = new Book(102, "Data Communications & Networking", "Forouzan", "Mc Graw Hill", 4);
         Book b3 = new Book(103, "Operating System", "Galvin", "Wiley", 6);
         // Adding Books to Deque
         set.add(b1);
         set.add(b2);
         set.add(b3);
         // Traversing ArrayDeque
         for (Book b : set) {
             System.out.println(b.id + " " + b.name + " " + b.author + " " + b.publisher + " " + b.quantity);
         }
    }
}

Output:

101 Let us C Yashwant Kanetkar BPB 8
102 Data Communications & Networking Forouzan Mc Graw Hill 4
103 Operating System Galvin Wiley 6

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Learn and master Java Collections Framework at Learn Java Collections Framework