# List structure and the composite design pattern  (Page 2/2)

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Is

• butter

a list?

Is

• 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.

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.

what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
how did you get the value of 2000N.What calculations are needed to arrive at it
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