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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

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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