Java Reference
In-Depth Information
class Image
{
// various member declarations
}
image for displaying on the screen. By convention, a class's name begins with an up-
percaseletter.Furthermore,thefirstletterofeachsubsequentwordinamultiwordclass
name is capitalized. This is known as
camelcasing
.
Creating Objects with the new Operator and a Constructor
Image
is an example of a user-defined type from which objects can be created. You
create these objects by using the
new
operator with a constructor, as follows:
Image image = new Image();
The
new
operator allocates memory to store the object whose type is specified by
new
'ssolitary operand, which happens to be
Image()
in this example. The object is
stored in a region of memory known as the
heap
.
Theparentheses(roundbrackets)thatfollow
Image
signifya
constructor
,whichis
a block of code for constructing an object by initializing it in some manner. The
new
operator
invokes
(calls)theconstructorimmediatelyafterallocatingmemorytostorethe
object.
Whentheconstructorends,
new
returnsa
reference
(amemoryaddressorotheriden-
tifier) totheobject sothat itcanbeaccessed elsewhere intheprogram.Regarding the
newlycreated
Image
object,itsreferenceisstoredinavariablenamed
image
whose
typeisspecifiedas
Image
.(It'scommontorefertothevariableasanobject,asinthe
image
object, although it stores only an object's reference and not the object itself.)
Note
new
's returned reference is represented in source code by keyword
this
.
Wherever
this
appears,itrepresentsthecurrentobject.Also,variablesthatstoreref-
erences are called
reference variables
.
Image
doesnotexplicitlydeclareaconstructor.Whenaclassdoesnotdeclareacon-
structor, Java implicitly creates a constructor for that class. The created constructor is
knownasthe
default noargument constructor
becausenoarguments(discussedshortly)
appear between its
(
and
)
characters when the constructor is invoked.
