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  • Restrict the users from seeing inside or working on the inside of the container.
  • Have simple put(data) and get() methods. Note the lack of specification of how the data goes in or comes out of the container.
  • However, a "policy" must exist that governs how data is added ("put") or removed ("get"). Examples:
    • First in/First out (FIFO) ("Queue")
    • Last in/First out (LIFO) ("Stack")
    • Retrieve by ranking ("Priority Queue")
    • Random retrieval
  • The policy is variant behavior -->abstract it.
    • The behavior of the RAC is independent of exactly what the policy does.
    • The RAC delegates the actual adding ("put") work to the policy.
    • The RAC is only dependent on the existence of the policy, not what it does.
    • The policy is a "strategy" for adding data to the RAC. See the Strategy design pattern .
    • Strategy pattern vs. State pattern -- so alike, yet so different!

The manufacturing of specific restricted access containers with specific insertion strategy will be done by concrete implementations of the following abstract factory interface.


package rac; /*** Abstract Factory to manufacture RACs. */public interface IRACFactory { /*** Returns an empty IRAContainer. */public IRAContainer makeRAC(); }


The following is an (abstract) implementation of IRACFactory using LRStruct as the underlining data structure. By varying the insertion strategy, which is an IAlgo on the internal LRStruct , we obtain different types of RAC: stack, queue, random, etc.

UML diagram of the abstract RAC and RAC factory definitions plus a few concrete RAC factories.

The source code for the following examples can be downloaded at this link .


package rac; import listFW.*;import listFW.factory.*; import lrs.*;/** * Implements a factory for restricted access containers. These* restricted access containers are implemented using an LRStruct to * hold the data objects.*/ public abstract class ALRSRACFactory implements IRACFactory {/** * Implements a general-purpose restricted access container using* an LRStruct. How? ** The next item to remove is always at the front of the list of * contained objects. This is invariant!* * Insertion is, however, delegated to a strategy routine; and* this strategy is provided to the container. This strategy * varies to implement the desired kind of container, e.g., queue * vs. stack.* * This nested static class is protected so that classes derived from its* factory can reuse it to create other kinds of restricted access * container.*/ protected static class LRSRAContainer implements IRAContainer {private IAlgo _insertStrategy; private LRStruct _lrs;public LRSRAContainer(IAlgo strategy) { _insertStrategy = strategy;_lrs = new LRStruct(); }/** * Empty the container.*/ public void clear() {_lrs = new LRStruct(); }/*** Return TRUE if the container is empty; otherwise, return * FALSE.*/ public boolean isEmpty() {return (Boolean)_lrs.execute(CheckEmpty.Singleton); }/** * Return TRUE if the container is full; otherwise, return* FALSE. ** This implementation can hold an arbitrary number of * objects. Thus, always return false.*/ public boolean isFull() {return false; }/** * Return an immutable list of all elements in the container.*/ public IList elements(final IListFactory fact) {return (IList)_lrs.execute(new IAlgo() { public Object emptyCase(LRStruct host, Object... nu) {return fact.makeEmptyList(); }public Object nonEmptyCase(LRStruct host, Object... nu) { return fact.makeNEList(host.getFirst(),(IList)host.getRest().execute(this)); }}); }/** * Remove the next item from the container and return it.*/ public Object get() {return _lrs.removeFront(); }/** * Add an item to the container.*/ public void put(Object input) {_lrs.execute(_insertStrategy, input); }public Object peek() { return _lrs.getFirst();} }} /*** Package private class used by ALRSRACFactory to check for emptiness of its internal LRStruct. */class CheckEmpty implements IAlgo { public static final CheckEmpty Singleton= new CheckEmpty();private CheckEmpty() { }public Object emptyCase(LRStruct host, Object... input) { return Boolean.TRUE;} public Object nonEmptyCase(LRStruct host, Object... input) {return Boolean.FALSE; }}


package rac; import lrs.*;public class LRSStackFactory extends ALRSRACFactory { /*** Create a ``last-in, first-out'' (LIFO) container. */public IRAContainer makeRAC() { return new LRSRAContainer(new IAlgo() {public Object emptyCase(LRStruct host, Object... input) { return host.insertFront(input[0]); }public Object nonEmptyCase(LRStruct host, Object... input) { return host.insertFront(input[0]); }}); }}


package rac; import lrs.*;public class LRSQueueFactory extends ALRSRACFactory { /*** Create a ``first-in, first-out'' (FIFO) container. */public IRAContainer makeRAC() { return new LRSRAContainer(new IAlgo() {public Object emptyCase(LRStruct host, Object... input) { return host.insertFront(input[0]); }public Object nonEmptyCase(LRStruct host, Object... input) { return host.getRest().execute(this, input);} });} }


package rac; import lrs.*;/* * Implements a factory for restricted access containers, including a* container that returns a random item. */public class RandomRACFactory extends ALRSRACFactory { /*** Create a container that returns a random item. */public IRAContainer makeRAC() { return new LRSRAContainer(new IAlgo() {public Object emptyCase(LRStruct host, Object... input) { return host.insertFront(input[0]); }public Object nonEmptyCase(LRStruct host, Object input) { /** Math.Random returns a value between 0.0 and 1.0. */if (0.5>Math.random()) return host.insertFront(input[0]); elsereturn host.getRest().execute(this, input); }}); }}

But can we push the abstraction further?  Is the difference between a stack and a queue really anything more than how the data is ordered?

Now, let's go on an look at the ordering object and priority queues...

Questions & Answers

I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
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How can I make nanorobot?
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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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