Java Collections (LIFO Structure)

Question

I am looking in the Collections framework of Java for a LIFO Structure (Stack) without any success. Basically I want a really simple stack; my perfect option would be a Deque, but I am in Java 1.5.

I would like not to have to add another class to my structure but I am wondering if that is possible:

1. Is there any class in the Collections framework (1.5) that does the job?

2. If not, is there any way to turn a Queue in a LIFO Queue (aka Stack) without reimplementation?

3. If not, which Interface or class should I extend for this task? I guess that keep the way that the guys of Sun have made with the Deque is a good start.

Thanks a lot.

EDIT: I forgot to say about the Stack class: I have my doubts about this class when I saw that it implements the Vector class, and the Vector class is a little bit obsolete, isn't it?

Solution 1

There's actually a Stack class: http://java.sun.com/j2se/1.5.0/docs/api/java/util/Stack.html

If you don't want to use that, the LinkedList class (http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedList.html) has addFirst and addLast and removeFirst and removeLast methods, making it perfect for use as a stack or queue class.

Solution 2

I realize I'm late to the party here, but java.util.Collections (Java 7) has a static 'asLifoQueue' that takes a Deque argument and returns (obviously) a LIFO queue view of the deque. I'm not sure what version this was added.

http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#asLifoQueue(java.util.Deque)

Solution 3

Deque, ArrayDeque, & LinkedList

While this was asked a while ago it might be wise to provide a JDK6+ answer which now provides a Deque (deck) interface which is implemented by the ArrayDeque data structure and the LinkedList was updated to implement this interface.

ConcurrentLinkedDeque & LinkedBlockingDeque

Specialised forms for concurrent access also exist and are implemented by ConcurrentLinkedDeque and LinkedBlockingDeque.

LIFO versus FIFO

The one thing that is great about a deque is that it provides both LIFO (stack) and FIFO (queue) support it can cause confusion as to which methods are for queue operations and which are for stack operations for newcomers.

IMHO the JDK should have a Stack interface and a Queue interface that could still be implemented by the likes of ArrayDeque but only expose the subset of methods required for that structure, i.e. a LIFO could define pop(), push() and peek(), then in the context of

LIFO<String> stack = new ArrayDeque<>();

only stack operations are exposed which stops someone accidentally calling add(E) when push(E) was intended.

Solution 4

Stack class is slowly: methods are synchronized + Stack extends synchronized Vector

Solution 5

There is a Stack class in the API. Will this meet your needs?

View more solutions

Comments

[Ken Gentle]

The main issue with Vector is that all access is synchronized, whether you need it or not. It is as "up-to-date" as any of the other collections, but got a bad reputation due to the synchronization issue.

[Spencer Kormos]

LinkedList also then provides the definition of a Deque, which is your desired collection.

[Charlie]

Sorry I forgot to Say about the Stack Class and my opinion about it, but I am thinking that probably is a better solution than implement my own class. isnt it?

[dma_k]

@SpencerKormos ... and LinkedList also supports null elements in contrast to ArrayDeque.

[Ivo]

The original post was using a Queue which was obviously FIFO and not LIFO, so I've updated my answer.

[Basil Bourque]

UPDATE This Answer is now outmoded. The Stack class has been supplanted by more modern classes, as explained in the Javadoc: A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. See the current solution in Answer by Brett Ryan and Answer by Ivan.