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  • bread
  • butter

a list?


  • butter

a list?

Is there a list that follows butter in the above?

A non-empty list is a list that has an element called first and a list called rest.

Note that in the above formulation, the rest of a list is itself a list! The definition of a list is an example of what we call a recursive definition: the list contains a substructure that is isomorphic to itself.

List design and the composite design pattern

The UML diagram below captures the recursive data definition of the list data structure.

Uml diagram of a list

A list can be represented using the composite design pattern

This definition translates into Java code as follows.

/** * Represents the abstract list structure.*/ public interface IList {}
/** * Represents empty lists.*/ public class MTList implements IList {} /** * Represents non-empty lists.*/ public class NEList implements IList {private Object _first; private IList _rest;}

The above is an example of what is called the composite design pattern . The composite pattern is a structural pattern that prescribes how to build a container object that is composed of other objects whose structures are isomorphic to that of the container itself. In this pattern, the container is called a composite. In the above, IList is called the abstract component, MTList is called the basic component and NEList is called the composite. The composite design pattern embodies the concept of recursion , one of the most powerful thinking tool in computing. (There is a subject in theoretical computer science and mathematics called "recursive function theory," which studies the meaning of what computing means and in effect defines in the most abstract form what a computer is and what it can and cannot do.)

List creation

Now that we have defined what a list is, we ask ourselves how we can process it? What can we do with a list? The above code makes it clear that there is not a whole lot we can do with a list besides instantiating a bunch of MTList objects via the call new MTList() (why?). Now that we are using the full Java language, we need to write a constructor for NEList in order to instantiate non-empty list objects with appropriate first and rest. The Java code for NEList now looks as follows (note how the comments are written).

/** * Represents non-empty lists.*/ public class NEList implements IList {private Object _first; private IList _rest;/** * Initializes this NEList to a given first and a given rest.* @param f the first element of this NEList. * @param r the rest of this NEList.*/ public NEList(Object f, IList r) {_first = f; _rest = r;} }

The list structure as coded in the above is completely encapsulated , that is, all internal components (if any) of a list are private and cannot be accessed by any external code. Using the appropriate constructors, we can make a bunch of lists to store data but we cannot retrieve data nor do anything with these lists. In Object-Oriented Programming (OOP) parlance, the list is said to have no behavior at all. As such they are of no use to us.

List processing

In order to perform any meaningful list processing at all, we need to program more "intelligence" into the list structure by adding appropriate methods to the list to provide the desired behaviors. So instead of asking what we can do with a list, the right question to ask in OOP is "what can a list do for us?" Let us start by presenting a few simple tasks that we want a list to perform and try to figure out how an "intelligent" list would carry out such tasks via some role acting.

In class role-acting exercises:

  • Compute the length of a list.
  • Compute the sum of a list that holds integers.

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, Design patterns. OpenStax CNX. Jun 04, 2009 Download for free at http://cnx.org/content/col10678/1.2
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