<< Chapter < Page Chapter >> Page >

Copy collection elements into an array

The code in Listing 6 shows how to use the simple version of the toArray method to create an array of type Object that contains a copy of each element in the LinkedList collection.

Listing 6 . Copy collection elements into an array.
Object[] array = ref.toArray();

The toArray method

Here is some of what Oracle has to say about this version of the toArray method:

"Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements arereturned by its iterator, this method must return the elements in the same order.
The returned array will be "safe" in that no references to it are maintained by this collection. ... The caller is thus free to modify thereturned array."

I will have some more to say about the safe aspects of the array shortly.

Display the array contents

The code in Listing 7 calls a method named showArray to cause the current contents of the array to be displayed.

Listing 7 . Display the array contents.
System.out.println("New array contents"); showArray(array);

The entire showArray method is shown in Listing 8 .

Listing 8 . The showArray method.
void showArray(Object[] array){for(int i = 0; i<array.length;i++){ if(array[i]== null){ System.out.print("null ");}else{ System.out.print(((JComponent)array[i]). getToolTipText() + " ");}//end else }//end for loopSystem.out.println(); }//end showArray()

The showArray method

The behavior of the ShowArray method is straightforward. The method uses a for loop to access each of the elements stored in the array in increasing index order.

A test is made to determine if the element contains a null reference. If so, then the word null is displayed for that element. If not, the getToolTipText method is used to access and display the value of the toolTipText property for each element in the array.

The output for the array

The output produced by the code in Listing 8 is shown below:

New array contents B0 B1 L2 B3 B4 L5

As you can see, (except for the String that identifies the type of output) this is an exact match to the output produced when the contents of thecollection were displayed.

How "safe" is the array?

While it is "safe" to modify the contents of the array as explained in the quotation from Oracle earlier, there is still some danger here that you need tobe aware of.

Java collections do not store objects. Rather, Java collections store references to objects. In Java, it is entirely possible to have two or morereferences to the same object.

Array contains copies of references to objects

Each element in the array is a copy of an element in the collection.

Therefore, at this point, for each object being managed by the collection, at least two references exist that refer to that object. One copy is contained inthe collection. The other copy is contained in the array.

If you use a reference stored in the array to modify the state of one of those objects, that modification is made to the object that is also referencedby an element in the collection. This may or may not be what you intend. It's not necessarily a problem as long as you understand what is going on and becareful how you use the references stored in the array.

Questions & Answers

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
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
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?