Java Reference
In-Depth Information
Display 6.8
String Processing Method with a Variable Number of Parameters
(part 2 of 2)
Sample Dialogue
What did you eat for dinner?
I ate salt cod, broccoli, french fries, salt peanuts, and apples.
You would be healthier if you could answer:
I ate cod, broccoli, peanuts, and apples.
The variable
arrayName
and the private instance variable
a
now contain the same refer-
ence, so both
arrayName
and the private instance variable
a
name the same array.
Using
arrayName
as a name for the array named by the private instance variable
a
, we
can now fill the indexed variables of
a
in any order and need not fill the array starting
at the first element. This violates the spirit of the
private
modifier for the array
instance variable
a
. For this reason, the accessor method
getInsideArray
should
return a deep copy of the array named by the private instance variable
a
. A safe defini-
tion of
getInsideArray
is the following:
public double
[] getInsideArray()
// Good version
{
//Recall that maxNumberElements == a.length.
double
[] temp =
new double
[maxNumberElements];
for
(
int
i = 0; i < maxNumberElements; i++)
temp[i] = a[i];
return
temp;
}
If a private instance variable is an array type that has a class as its base type, then
you need to be sure to make copies of the class objects in the array when you make a
copy of the array. This is illustrated by the toy class in Display 6.9.
Display 6.9 also includes a copy constructor. As illustrated in that display, the copy
constructor should make a completely independent copy of the array instance variable
(that is, a deep copy) in the same way that the accessor method does. This same point
is also illustrated by the copy constructor in Display 6.5.
Display 6.9
Accessor Method for an Array Instance Variable
1
/**
2
Demonstrates the correct way to define an accessor
3
method to a private array of class objects.
4
*/
5
public class
ToyExample
6{
7
The class
Date
is defined in Display 4.11, but
you do not need to know the details of the
definition to understand the point of this
example.
private
Date[] a;
