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Display the collection's contents

Then, as before, the code in Listing 4 gets an iterator and uses it to access and display the contents of the ArrayList collection.

The ArrayList class implements the List interface, which does not prohibit duplicate elements, and does not maintain its elements in sortedorder. Therefore, in this case, the following text was displayed:


All five element values are displayed, including the duplicate, in the order in which they were added to the list.

The important point

The important point is that although the fillIt method calls the same method name ( add ) on each of the collection objects, the behavior of that method is different in each case. In both cases, the behavior isappropriate for the underlying data structure. Furthermore, the underlying data structure isn't even known to the fillIt method.

No duplicate elements in ascending order

In the first case, where the underlying data structure was a TreeSet object (type SortedSet ), the duplicate element was eliminated, and the elements were stored so as to be accessible in ascending order.

Duplicates allowed with no sorting

In the second case, where the underlying data structure was an ArrayList object (type List ), all five elements, including the duplicate element were stored in the collection. Furthermore, they were stored and laterretrieved in the same order in which they were added.

Structure of the core interfaces

The core collection interfaces in the Java Collections Framework do not all extend from a common root interface.

Rather, the inheritance structure of the core interfaces is shown below. Indentation is used to indicate the parent-child relationships among the interfaces.

  • Collection
    • Set
      • SortedSet
    • List
    • Queue
    • Deque
  • Map
    • SortedMap

A Map is not a true Collection

As you can see, that there is no common root interface. Rather, there are two distinct trees, one rooted by Collection and the other rooted by Map . According to The Java Tutorial from Oracle, "a Map is not a true Collection." I will have more to say about this in a future module.

Some operations are optional

Every class that implements an interface in the tree rooted in Collection is not required to support all of the methods (operations) declared in the Collection interface.

Rather, some of the methods in the Collection interface are designated as "optional operation" in the documentation. (See the list of optional methods for the Collection interface below.)

According to the contract for the Collections Framework, if a given implementation doesn't support a specific method, it must throw an UnsupportedOperationException . The author of the implementation is responsible for providing documentation that identifies the optional operationsthat the implementation does and does not support.

Support for optional operations

This should not be an issue unless you are either defining your own implementation, or using an implementation defined by someone other than theprogrammers at Oracle. All of the general-purpose implementations from Oracle appear to support all of the optional operations.

Questions & Answers

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
Do somebody tell me a best nano engineering book for beginners?
s. Reply
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?
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
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
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