Java Reference
In-Depth Information
P
ROGRAMMING
T
IP
•
Writing Java statements that test a class's methods will help you to fully understand the specifications for the
methods. Obviously, you must understand a method before you can implement it correctly. If you are also
the class designer, your use of the class might help you see desirable changes to your design or its documen-
tation. You will save time if you make these revisions before you have implemented the class. Since you
must write a program that tests your implementation sometime, why not get additional benefits from the task
by writing it now instead of later?
E
XERCISES
1.
Specify each method of the class
PiggyBank
, as given in Listing 1-3, by stating the method's purpose; by
describing its parameters; and by writing preconditions, postconditions, and a pseudocode version of its header.
Then write a Java interface for these methods that includes
javadoc
-style comments.
2.
Suppose that
groceryBag
is a bag filled to its capacity with 10 strings that name various groceries. Write Java state-
ments that remove and count all occurrences of
"soup"
in
groceryBag
. Do not remove any other strings from the
bag. Report the number of times that
"soup"
occurred in the bag. Accommodate the possibility that
groceryBag
does not contain any occurrence of
"soup"
.
3.
Given
groceryBag
, as described in Exercise 2, what effect does the operation
groceryBag.toArray()
have on
groceryBag
?
4.
Given
groceryBag
, as described in Exercise 2, write some Java statements that create an array of the distinct strings
that are in this bag. That is, if
"soup"
occurs three times in
groceryBag
, it should only appear once in your array.
After you have finished creating this array, the contents of
groceryBag
should be unchanged.
5.
The
union
of two collections consists of their contents combined into a new collection. Add a method
union
to the
interface
BagInterface
for the ADT bag that returns as a new bag the union of the bag receiving the call to the
method and the bag that is the method's one argument. Include sufficient comments to fully specify the method.
Note that the union of two bags might contain duplicate items. For example, if object
x
occurs five times in one
bag and twice in another, the union of these bags contains
x
seven times. Specifically, suppose that
bag1
and
bag2
are
Bag
objects, where
Bag
implements
BagInterface
;
bag1
contains the
String
objects
a
,
b
, and
c
; and
bag2
contains
the
String
objects
b
,
b
,
d
, and
e
. After the statement
BagInterface<String> everything = bag1.union(bag2);
executes, the bag
everything
contains the strings
a
,
b
,
b
,
b
,
c
,
d
, and
e
. Note that
union
does not affect the con-
tents of
bag1
and
bag2
.
6.
The
intersection
of two collections is a new collection of the entries that occur in both collections. That is, it con-
tains the overlapping entries. Add a method
intersection
to the interface
BagInterface
for the ADT bag that
returns as a new bag the intersection of the bag receiving the call to the method and the bag that is the method's
one argument. Include sufficient comments to fully specify the method.
Note that the intersection of two bags might contain duplicate items. For example, if object
x
occurs five
times in one bag and twice in another, the intersection of these bags contains
x
twice. Specifically, suppose that
bag1
and
bag2
are
Bag
objects, where
Bag
implements
BagInterface
;
bag1
contains the
String
objects
a
,
b
, and
c
; and
bag2
contains the
String
objects
b
,
b
,
d
, and
e
. After the statement
BagInterface<String> commonItems = bag1.intersection(bag2);
executes, the bag
commonItems
contains only the string
b
. If
b
had occurred in
bag1
twice,
commonItems
would
have contained two occurrences of
b
, since
bag2
also contains two occurrences of
b
. Note that
intersection
does
not affect the contents of
bag1
and
bag2
.
