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Gives the basics of array storage, with examples of basic array processing in Java, and contrasts arrays with lists.

There are many ways to store data. So far, we have covered linear recursive structures, lists, and binary recursive structures, trees. Let's consider another way of storing data, as a contiguous, numbered (indexed) set of data storage elements:

anArray =

itemA itemB itemC itemD itemE itemF itemG itemH itemI itemJ
0 1 2 3 4 5 6 7 8 9

This " array " of elements allows us to access any individual element using a numbered index value.

At its most basic form, a random access data structure where any element can be accessed by specifying a single index value corresponding to that element.
Notice however, that the above definition is not a recursive definition. This will cause problems.

Arrays in java

  • Arrays...
    • are contiguous (in memory) sets of object references (or values, for primitives),
    • are objects,
    • are dynamically created (via new ), and
    • may be assigned to variables of type Object or primitives
  • An array object contains zero or more unnamed variables of the same type. These variables are commonly called the elements of the array.
  • A non-negative integer is used to name each element. For example, arrayOfInts[i] refers to the i+1 st element in the arrayOfInts array. In computer-ese, an array is said to be a "random access" container, because you can directly (and I suppose, randomly) access any element in the array.
  • An array has a limited amount of intelligence, for instance, it does know its maximum length at all times, e.g. arrayOfInts.length .
  • Arrays have the advantage that they
    • provide random access to any element
    • are fast.
    • require minimum amounts of memory

More information on arrays can be found in the Java Resources web site page on arrays

Arrays are size and speed at a price.

Array types

  • An array type is written as the name of an element type followed by one or more empty pairs of square brackets.
    • For example, int[] is the type corresponding to a one-dimensional array of integers.
  • An array's length is not part of its type.
  • The element type of an array may be any type, whether primitive or reference, including interface types and abstract class types.

Array variables

  • Array variables are declared like other variables: a declaration consists of the array's type followed by the array's name. For example, double[][]matrixOfDoubles; declares a variable whose type is a two-dimensional array of double-precision floating-point numbers.
  • Declaring a variable of array type does not create an array object. It only creates the variable, which can contain a reference to an array.
  • Because an array's length is not part of its type, a single variable of array type may contain references to arrays of different lengths.
  • To complicate declarations, C/C++-like syntax is also supported, for example, double rowvector[], colvector[], matrix[][]; This declaration is equivalent to double[] rowvector, colvector, matrix[]; or double[] rowvector, colvector;double[][]matrix; Please use the latter!

Array creation

  • Array objects, like other objects, are created with new . For example, String[] arrayOfStrings = new String[10]; declares a variable whose type is an array of strings, and initializes it to hold a reference to an array object with room for ten references to strings.
  • Another way to initialize array variables is int[] arrayOf1To5 = { 1, 2, 3, 4, 5 };String[] arrayOfStrings = { "array","of", "String" };Widget[] arrayOfWidgets = { new Widget(), new Widget() };
  • Once an array object is created, it never changes length! int[][]arrayOfArrayOfInt = {{ 1, 2 }, { 3, 4 }};
  • The array's length is available as a final instance variable length. For example, int[] arrayOf1To5 = { 1, 2, 3, 4, 5 };System.out.println(arrayOf1To5.length); would print ``5''.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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.
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
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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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