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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

who was the first nanotechnologist
Lizzy Reply
technologist's thinker father is Richard Feynman but the literature first user scientist Nario Tagunichi.
Norio Taniguchi
I need help
anyone have book of Abdel Salam Hamdy Makhlouf book in pdf Fundamentals of Nanoparticles: Classifications, Synthesis
Naeem Reply
what happen with The nano material on The deep space.?
pedro Reply
It could change the whole space science.
the characteristics of nano materials can be studied by solving which equation?
sibaram Reply
plz answer fast
synthesis of nano materials by chemical reaction taking place in aqueous solvents under high temperature and pressure is call?
hydrothermal synthesis
how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where is the latest information on a no technology how can I find it
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
STM - Scanning Tunneling Microscope.
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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
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