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Array accesses

  • Indices for arrays must be int values that are greater than or equal to 0 and less than the length of the array. Remember that computer scientists always count starting at zero, not one!
  • All array accesses are checked at run time: An attempt to use an index that is less than zero or greater than or equal to the length of the array causes an IndexOutOfBoundsException to be thrown.
  • Array elements can be used on either side of an equals sign:
    • myArray[i] = aValue;
    • someValue = myArray[j];
  • Accessing elements of an array is fast and the time to access any element is independent of where it is in the array.
  • Inserting elements into an array is very slow because all the other elements following the insertion point have to be moved to make room, if that is even possible.

Array processing using loops

More information on loops can be found at the Java Resources web site page on loops .

The main technique used to process arrays is the for loop . A for loop is a way of processing each element of the array in a sequential manner.

Here is a typical for loop:

// Sum the number of elements in an array of ints, myArray. int sum = 0; // initialize the sumfor(int idx=0; idx<myArray.length; idx++) { //start idx @ 0; end idx at length-1; //increment idx every time the loop is processed.sum += myArray[idx]; // add the idx'th element of myArray to the sum}

There are a number of things going on in the above for loop:

  • Before the loop starts , the index idx is being declared and initialized to zero. idx is visible only within the for loop body (between the curly braces).
  • At the begnning of each loop iteration , the index idx is being tested in a "termination condition", in this case, idx is compared to the length of the list. If the termination condition evaluates to false , the loop will immediately terminate.
  • During each loop iteration , the value of the idx 's element in the array is being added to the running sum.
  • After each loop iteration , the index idx is being incremented.

One can traverse an array in any direction one wishes:

// Sum the number of elements in an array of ints, myArray. int sum = 0; // initialize the sumfor(int idx=myArray.length-1; 0<=idx; idx--) { //start idx @ length-1; end idx at 0; //decrement idx every time the loop is processed.sum += myArray[idx]; // add the idx'th element of myArray to the sum}

The above loop sums the list just as well as the first example, but it does it from back to front. Note however, that we had to be a little careful on how we initialized the index and how we set up the termination condition.

Here's a little more complicated loop:

// Find the index of the smallest element in an array of ints, myArray. int minIdx = 0; // initialize the index. Must be declared outside the loop.if(0==myArray.length) throw new NoSuchElementException("Empty array!"); //No good if array //is empty!else { for(minIdx = 0, int j = 1; j<myArray.length; j++) { //start minIdx @ 0, start index @ 1; //end index at length-1; increment// index every time the loop is //processed.if(myArray[minIdx]>myArray[j])minIdx = j; // found new minimum }}

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, Principles of object-oriented programming. OpenStax CNX. May 10, 2013 Download for free at http://legacy.cnx.org/content/col10213/1.37
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