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These learning objects explain arrays in the Java program language. Arrays are a data structure for efficiently accessing a large number of components of the same type.

Learning objects for arrays

Concept An array is a sequence of elements of the same type; the type of the elements can be a primitive types such as int , or a predefined or user-defined class type. To access an element of an array, an index is given; this may be any expression of type int , including an integer literal or a variable.

The source code of these learning objects can be found in array.zip .

LO Topic Java Files (.java) Prerequisites
"Array objects" Array objects Array01A, B
"Array initializers" Array initializers Array02 1
"Passing arrays as parameters" Passing arrays as parameters Array03 2
"Returning an array from a method" Returning an array from a method Array04 2
"Array assignment can create garbage" Array assignment can create garbage Array05 4
"Two-dimensional arrays" Two-dimensional arrays Array06 3
"Arrays of arrays" Arrays of arrays Array07 6
"Ragged Arrays" Ragged arrays Array08 6
"Arrays of objects" Arrays of objects Array09 3

The example used in LO 1 through LO 4 is to fill an array with a sequence of fibonacci numbers (0,1,1,2,3,5,8). The programs forLO 5 through LO 8 concern matrices. The program for LO 9 is explained there.

Array objects

Concept An array is created in three steps: first a variable of an array type is declared; then the array is allocated; finally, theelements of the array are given values. The syntax for accessing an array a is a[i] , and the field a.length gives the length of the array, so that if we modify the program by changing the sizeof the array the rest of the program need not change.

Program: Array01A.java

// Learning Object Array01A //    array objectspublic class Array01A {     public static void main(/*String[] args*/) {         int[] fib;         fib = new int[7];         fib[0] = 0;         fib[1] = 1;         for (int i = 2; i < fib.length; i++)             fib[i] = fib[i-1] + fib[i-2];     }}

The program creates an array in the three steps described above.

  • Initially, the variable fib of type integer array (denoted int[] ) is allocated and contains the null value.
  • new fib[7] creates an array object with its seven fields having the default integer value zero; then the reference to the object is returned and stored in the variable fib .
  • The length field of the array is displayed above the cells for the elements.
  • A for loop is used to assign values to each element of the array.
  • The thin white lines show the constants and expressions that are used as indices into the array.
  • Automatic dereferencing : Although expressions like fib[i-2] seem to indicate that fib is being indexed, fib contains a reference to an array; an implicit operation of dereferencing is carried out to obtain thearray itself from the reference and the index [i-2] is then applied to that array.

Concept It is possible to combine the first two steps in creating an array: declaring the array field and allocating the array object.

Program: Array01B.java

Questions & Answers

what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
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a perfect square v²+2v+_
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algebra 2 Inequalities:If equation 2 = 0 it is an open set?
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or infinite solutions?
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rolling four fair dice and getting an even number an all four dice
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Kristine 2*2*2=8
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Differences Between Laspeyres and Paasche Indices
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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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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