Java Community | Help. Code. Learn.•6d ago

Stack Interface, Deque Implementation: Worth it?

First time poster here, so please be lenient :) I have learned that the Stack class in Java inherits Vector class, which breaks LIFO contract. I also learned that Deque (a double-ended queue, seems contradictory) does not strictly maintain LIFO contract and is not thread-safe as far as I know (though this can be solved with ConcurrentLinkedDeque). Anyway, I have found a solution being: Defining a Stack interface

public interface Stack<E> {
    void push(E item);
    E pop();
    E peek();
    boolean isEmpty();
}

public interface Stack<E> {
    void push(E item);
    E pop();
    E peek();
    boolean isEmpty();
}

Defining a DequeStack class implementing Stack

public class DequeStack<E> implements Stack<E> {
    private final Deque<E> deque = new ArrayDeque<E>();

    @Override
    public void push(E item) {
        deque.addFirst(item);
    }

    @Override
    public E pop() {
        return deque.removeFirst();
    }

    @Override
    public E peek() {
        return deque.peekFirst();
    }

    @Override
    public boolean isEmpty() {
        return deque.isEmpty();
    }
}

public class DequeStack<E> implements Stack<E> {
    private final Deque<E> deque = new ArrayDeque<E>();

    @Override
    public void push(E item) {
        deque.addFirst(item);
    }

    @Override
    public E pop() {
        return deque.removeFirst();
    }

    @Override
    public E peek() {
        return deque.peekFirst();
    }

    @Override
    public boolean isEmpty() {
        return deque.isEmpty();
    }
}

My main issue simply: Is this even worth it? Are there cases where this would be necessary? Perhaps a specific case such as RPN implementation or can one still get away with using Deque? Also, are there potential alternatives to this? Should Stack class still be used as is or should Deque interface be implemented normally (for example, using ArrayDeque)? I tried looking online but most seemed to suggest either using Deque as is or provided the solution above, though nobody seemed to discuss the point/necessity of this.

23 Replies

JavaBot•6d ago

⌛ This post has been reserved for your question.

Hey @Wither Well! Please use /close or the Close Post button above when your problem is solved. Please remember to follow the help guidelines. This post will be automatically marked as dormant after 300 minutes of inactivity.

TIP: Narrow down your issue to simple and precise questions to maximize the chance that others will reply in here.

Peter Rader•6d ago

Stack fulfil LIFO, it doesnt break it?! From the javadoc: The Stack class represents a last-in-first-out (LIFO) stack of objects

dan1st•5d ago

The Stack class satisfies LIFO but - it shouldn't be used any more - you are also able to insert remove and replace arbitrary elements just use ArrayDeque directly

Wither WellOP•5d ago

Stack class inherits from Vector class which has methods such as indexOf(), elementAt(), setElementAt(), insertElementAt() which are methods that allows indexed access, this breaks LIFO contract. The Java API for Stack class encourages the usage of Deque over Stack. However, I am not trying to discuss the validity of Stack class as a LIFO object. Instead, I am trying to discuss why such solutions have been made in the first place (I have not created this solution myself, I found them online). As indicated by the title; is it worth it to have such solutions? I am more so questioning the point of creating such a solution rather than whether I myself should use such solution. I am curious about it because I have seen two articles/posts regarding Java's Stack and simply wondered, "why"?

dan1st•5d ago

You mean you are asking why Stack exists? Stack is older than ArrayDeque and most other parts of the collection API and removing it would break compatibility @Wither Well it's because of the masked links

Wither WellOP•5d ago

I am sorry but I am unsure what you mean by "masked links".

dan1st•5d ago

[text](https://some link)

Wither WellOP•5d ago

Ah, right. Yeah, I had checked the rules and was unsure what the problem is. Thanks! Would you perhaps like if I still link the articles?

dan1st•5d ago

and that's why your message was blocked which articles?

Wither WellOP•5d ago

There were two articles I read that complained about both Stack and Deque not strictly maintaining LIFO contract, and both offered the solution I showed above (defining a Stack interface and implementing it). I was just wondering why that would be an issue. If an ArrayDeque is functionally used as a Stack, so technically showing a LIFO behavior, would it be an issue if it still has certain methods that would allow it to break LIFO contract?

dan1st•5d ago

oh I misread your message

Wither WellOP•5d ago

I just do not quite understand why being so strict about LIFO contract is really critical and was wondering if there were instances where that would be important.

dan1st•5d ago

I might be able to look at them but not now

Wither WellOP•5d ago

No problem, I should have been clear!

dan1st•5d ago

well they just have some additional operatios you can use, that's all it's normally not an issue

Wither WellOP•5d ago

So it would not be necessary to try to implement a strict LIFO contract right? Like, the whole thing about "Does not maintain strict LIFO contract" feels like a non-issue. Is it fair that's how I feel about this?

dan1st•5d ago

it is pretty much a non-issue unless you use it as part of some API and you want to make sure others with access to that object don't (accidentially) do that stuff with it But even there, ArrayDeque only allows you to add stuff at the beginning or end

Wither WellOP•5d ago

Right, I understand. Well, that's all. Thank you very much for your help!

JavaBot•5d ago

If you are finished with your post, please close it. If you are not, please ignore this message. Note that you will not be able to send further messages here after this post have been closed but you will be able to create new posts.

Wither WellOP•5d ago

I will link the articles in case someone visits this post and wants to read

Wither WellOP•5d ago

https://baddotrobot.com/blog/2013/01/10/stack-vs-deque/ https://www.happycoders.eu/algorithms/stack-implementation-java/

Java Stack vs Deque - bad.robot

Oracle broke encapsulation with their Stack implementation and haven't bothered fixing it and instead recommend using Deque instead.

HappyCoders.eu

Stack Implementation in Java

In this tutorial, you will learn how to implement a stack in Java - with an ArrayDeque, an Array, a LinkedList and a Queue.

Wither WellOP•5d ago

Thanks again for your help

JavaBot•5d ago

Post Closed

This post has been closed by <@1352211901953740850>.

Gaming

Programming

Stack Interface, Deque Implementation: Worth it?

Did you find this page helpful?