<< Chapter < Page Chapter >> Page >

Exercise Instead of declaring the variable j outside the for-loop, declare it just inside the for-loop as follows:

int j = a.length-i-1;

Trace the execution and explain what happens.

Returning an array from a method

Concept An array can be allocated within a method. Although the variable containing the reference to the array is local to the method, the arrayitself is global and the reference can be returned from the method.

Program: Array04.java

// Learning Object Array04 //    returning an array from a methodpublic class Array04 {     static int[] reverse(int[] a) {        int[] b = new int[a.length];         int j;        for (int i = 0; i < a.length / 2; i++) {             j = a.length-i-1;            b[j] = a[i];             b[i] = a[j];        }         return b;    }      public static void main(/*String[] args*/) {         int[] fib = {0, 1, 1, 2, 3, 5, 8};         int[] reversedFib = reverse(fib);     }}

This program passes an array as a parameter to a method that reverses the elements of the array. The array is reversed into a new array b that is allocated in the method reverse . It is then returned to the main method and assigned to reversedFib , a different variable of the same array type int[] .

  • Initially, the variable fib of type integer array is allocated. As part of the same statement, the array object is created withits seven fields having the values in the initializer; the reference to the object is returned and stored in the variable fib .
  • A reference to the array is passed as a parameter to the method reverse . The formal parameter a contains a reference to the same array pointeed to by the actual parameter fib .
  • A new array b of the same type and length as the parameter a is declared and allocated.
  • Each iteration of the for-loop moves one element from the first half of a to the second half of b and one element from the second half of a to the first half of b . Variables i and j contain the indices of the two elements that are moved.
  • The reference to array b is returned. Although array referenced by b was allocated within the method call, it still exists after returning.
  • The reference that is returned is assigned to reversedFib .

Exercise The program has a bug. Fix it!

Array assignment can create garbage

Concept Since an array variable contains a reference to the array itself, if null or another value (another array of the same type) is assigned to the variable, the first array may no longer be accessible. Inaccessible memoryis called garbage . The Java runtime system includes a garbage collector whose task is to return garbage to the pool of memory that can be allocated.

Program: Array05.java

// Learning Object Array05 //    array assignment can create garbagepublic class Array05 {     static int[] first(int[] a) {        int[] b = new int[a.length/2];         for (int i = 0; i < a.length / 2; i++)             b[i] = a[i];        return b;     }      public static void main(/*String[] args*/) {         int[] fib = {0, 1, 1, 2, 3, 5, 8};         fib = first(fib);    } }

An array referenced by the variable fib is passed as a parameter to a method that moves the values of the elements in the first half of the array fib into a new array b which is allocated in the method. The new array is returned to the main method and assigned to the variable fib , destroying the reference to the original array.

Questions & Answers

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
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
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.
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
Berger describes sociologists as concerned with
Mueller Reply
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, Learning objects for java (with jeliot). OpenStax CNX. Dec 28, 2009 Download for free at http://cnx.org/content/col10915/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Learning objects for java (with jeliot)' conversation and receive update notifications?