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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

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
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.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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Source:  OpenStax, Learning objects for java (with jeliot). OpenStax CNX. Dec 28, 2009 Download for free at http://cnx.org/content/col10915/1.2
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