<< Chapter < Page Chapter >> Page >

Instantiate and populate an ArrayList object

One of the capabilities of the Collection Framework is to create a new Collection object and populate it with the contents of an existing Collection object of a different (or the same) actual type.

The code in Listing 3 instantiates an ArrayList object and populatesit with the contents of the existing TreeSet object. As a result, we then have two different Collection objects of different actual types containing the same elements.

Listing 3 . Instantiate and populate an ArrayList object.
Collection aList = new ArrayList(aTree);

Identify a target element

The objective of this program is to compare the times required to search for and to find an element in each of the collections. Thus, we need a target elementto search for.

The code in Listing 4 extracts a value near the center of the ArrayList object using an index to find and extract the value. This is a very fast operation on a List object. This value is saved in testVal to be used later for test purposes.

Note that the reference to the ArrayList object was saved as type Collection (and not as type ArrayList ) in Listing 3 above.

Note also that it was necessary to cast that reference to type List in Listing 4 in order to call the get method on the reference. This is because the Collection interface does not declare a method named get . Rather, the get method is added to the List interface to define a more specialized form of collection.

(Author's note: This program was originally written before the introduction of Generics. The above requirement may not be true if the programwere to be rewritten making proper use of Generics.)
Listing 4 . Identify a target element.
Object testVal = ((List)aList).get(size/2);

Search for the test value in each collection

The code in Listing 5 calls the contains method to search for the test value in each of the collections. It uses the system clock to measurethe time required to find the element in each case. (I will assume that you understand how to use the Date class for this purpose, and won't provide a detailed explanation.)

Listing 5 . Search for the test value in each collection.
long start = new Date().getTime(); boolean found = aList.contains(testVal);long stop = new Date().getTime(); System.out.println(found + " " + (stop - start));start = new Date().getTime(); for(int x = 0; x<100000; x++){ found = aTree.contains(testVal);}//end for loop stop = new Date().getTime();System.out.println(found + " " + (stop - start)/100000.0); }//end doIt()

Program output

Running the program several times produced the following range of output values:

  • First output value ranged from "true 93" to "true 109"
  • Second output value ranged from "true 0.00031" to "true 0.00046"

The first output value applies to the ArrayList object, and the second output value applies to the TreeSet object.

As we would expect, the test value was successfully found in both cases; hence the display of true in both cases.

Time required to search the ArrayList collection

The output indicates that approximately 100 milliseconds were required to find the test value in the ArrayList object.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
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
how can I make nanorobot?
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
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?