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Restricted access containers provided encapsulated storage of information for algorithms where the storage is decoupled from the details of insertion and removal of data from the storage.

Introduction

Stacks and queues are examples of containers with special insertion and removal behaviors and a special access behavior.

Insertion and removal in a stack must be carried out in such a way that the last data inserted is the first one to be removed.  One can only retrieve and remove a data element from a stack by way of special access point called the "top".  Traditionally, the insertion and removal methods for a stack are called push and pop, respectively. push inserts a data element at the top of the stack. pop removes and returns the data element at the top of the stack. A stack is used to model systems that exhibit LIFO (Last In First Out) insert/removal behavior. 

Data insertion and removal in a queue must be carried out in such a way that the first one to be inserted is the first one to be removed.  One can only retrieve and remove a data element from a queue by way of special access point called the "front". Traditionally, the insertion and removal methods for a queue are called enqueue and dequeue , respectively. enqueue inserts a data element at the "end" of the queue. dequeue removes and returns the data element at the front of the queue. A queue is used to model systems that exhibit FIFO (First In First Out) insertion/removal behavior. For example, one can model a movie ticket line by a queue.

We abstract the behaviors of special containers such as stacks and queues into an interface called IRAContainer specified as follows.

Restricted access containers

Iracontainer.java

package rac; import listFW.*;/** * Defines the interface for a restricted access container.*/ public interface IRAContainer {/** * Empty the container.* NOTE: This implies a state change. * This behavior can be achieved by repeatedly removing elements from this IRAContainer.* It is specified here as a convenience to the client. */public void clear(); /*** Return TRUE if the container is empty; otherwise, return * FALSE.*/ public boolean isEmpty();/** * Return TRUE if the container is full; otherwise, return* FALSE. */public boolean isFull(); /*** Return an immutable list of all elements in the container. * @param fact for manufacturing an IList.*/ public IList elements(IListFactory fact);/** * Remove the next item from the container and return it.* NOTE: This implies a state change. * @throw an Exception if this IRAContainer is empty.*/ public Object get();/** * Add an item to the container.* NOTE: This implies a state change. * @param input the Object to be added to this IRAContainer.* @throw an Exception if this IRAContainer is full. */public void put(Object input); /*** Return the next element in this IRAContainer withour removing it. * @throw an Exception if this IRAContainer is empty.*/ public Object peek();}

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Source:  OpenStax, Principles of object-oriented programming. OpenStax CNX. May 10, 2013 Download for free at http://legacy.cnx.org/content/col10213/1.37
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