Review:
array of primitive variables
Previously, we
learned how to
create
an
array of
primitive typed
variables:
double[] numbers;
Result: 
numbers = new double[100];
Result: 
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Note:
numbers[i] is
a
double variable
and
can
store a
number
Array of
of reference variables
that point to objects
Similiarly, you can
create
an
array of
reference variables:
Circle[] circleArray;
Result: 
circleArray = new Circle[10];
Result: 
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Note:
circleArray[i] is
a
Circle reference variable and
can
store a
reference
to a Circle object
Array of
of reference variables
that point to objects
In other words:
we can create a
Circle object with
new and
assign it to
an array element:
circleArray = new Circle[10];
Result:
circleArray[0] = new Circle(4);
Result: 
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Note:
circleArray[i] is
a
Circle reference variable and
can
store a
reference
to a Circle object
Contrasting
an array of primitive type variables and
an array of reference
type variables
What is
an array of
primitive typed variables
and
an array of
reference variables:
- After
creating an
array of
primitive variables,
each array element can
store a
value:
double[] numbers = new double[100];
numbers[0] = 99; // We can store a number
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- After
creating an
array of
reference variables,
each array element can
store a
reference of
an object:
Circle[] circleArray = new Circle[10];
circleArray[0] = new Circle(2.0);
// Stores a reference to a circle object
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Contrasting
an array of primitive type variables and
an array of reference
type variables
The use of
primitive type
variables and
reference type
variables are
different:
- Primitive type
array variables
(number[k])
contains
values and
is used in
computations:
double[] numbers = new double[100];
numbers[0] = 99;
sum = sum + numbers[0]; // number[0] is a double
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- Reference type
array variables
(circleArray[k])
contains
references and
is used with the
member selection operator
. :
Circle[] circleArray = new Circle[10];
circleArray[0] = new Circle(2.0);
double area = circleArray[0].getArea();
// circleArray[0] is a Circle reference
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Using an
array of objects
- Array of
objects is
frequently used in
computer programs
- In the next set of
slides,
I will
show you
how to use
an
array
of Card
to
represent
a
deck of playing cards
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