Discovering Classes and Objects - Beginning Java 7 - page 72

Forexample,youcanuse new tocreateaone-dimensionalarrayofobjectreferences,
asdemonstratedbythefollowingexample,whichcreatesaone-dimensionalarraythat
can store ten Image object references:
Image[] imArray = new Image[10];
Whenyoucreateaone-dimensionalarray, new zerosthebitsineacharrayelement's
storage location, which you interpret at the source code level as literal value false ,
'\u0000' , 0 , 0L , 0.0 , 0.0F ,or null (dependingonelementtype).Intheprevious
example,eachof imArray 'selementsisinitializedto null ,whichrepresentsthe null
reference (a reference to no object).
Aftercreatinganarray,youneedtoassignobjectreferencestoitselements.Thefol-
lowing example demonstrates this task by creating Image objects and assigning their
references to imArray elements:
for (int i = 0; i < imArray.length; i++)
imArray[i] = new Image("image"+i+".png"); // image0.png,
image1.png, and so on
The "image"+i+".png" expressionusesthestringconcatenationoperator( + )to
combine image withthestringequivalentoftheintegervaluestoredinvariable i with
.png .Theresultingstringispassedto Image 's Image(String filename) con-
structor.
Caution Use of the string concatenation operator in a loop context can result in a
lotofunnecessary String objectcreation,dependingonthelengthoftheloop.Iwill
discuss this topic in Chapter 4 when I introduce you to the String class.
You can also use new to create arrays of primitive type values (such as integers
or double precision floating-point numbers). For example, suppose you want to create
a two-dimensional three-row-by-two-column array of double precision floating-point
temperature values. The following example accomplishes this task:
double[][] temperatures = new double[3][2];
After creating a two-dimensional array, you will want to populate its elements with
suitable values. The following example initializes each temperatures element,
whichisaccessedas temperatures[row][col] ,toarandomlygeneratedtemper-
ature value via Math.random() , which I'll explain in Chapter 4 :
for (int row = 0; row < temperatures.length; row++)
for (int col = 0; col < temperatures[row].length; col++)
temperatures[row][col] = Math.random()*100;