Java Reference
In-Depth Information
The bag contains the following string(s):
A B A C B C D
Testing the method isFull with a full bag:
isFull finds the bag full: OK.
2.15
Notice that, in addition to the
main
method,
ArrayBagDemo1
has three other methods. Since
main
is
static and calls these other methods, they must be static as well. The method
testAdd
accepts as its
arguments a bag and an array of strings. The method uses a loop to add each string in the array to
the bag. The method
testIsFull
takes a bag as its argument and a boolean value that indicates the
value we expect
isFull
to return if its logic is correct. Finally, the method
displayBag
takes a bag
as its argument and uses the bag's method
toArray
to access its contents. Once we have an array of
the bag's entries, a simple loop can display them.
Question 8
What is the result of executing the following statements within the
main
method of
BagDemo1
?
ArrayBag<String> aBag =
new
ArrayBag<String>();
displayBag(aBag);
Now that we can add objects to a bag, we can implement the remaining methods, beginning with the eas-
iest ones. We will postpone the definitions of
remove
momentarily until we see how to search a bag.
2.16
The methods
isEmpty
and
getCurrentSize
.
The methods
isEmpty
and
getCurrentSize
have
straightforward definitions, as you can see:
/** Sees whether this bag is empty.
@return true if the bag is empty, or false if not */
public boolean
isEmpty()
{
return
numberOfEntries == 0;
}
// end isEmpty
/** Gets the current number of entries in this bag.
@return the integer number of entries currently in the bag */
public int
getCurrentSize()
{
return
numberOfEntries;
}
// end getCurrentSize
Note:
The definitions of some methods are almost as simple as the stubs you might use to
define them in an early version of a class. Such is the case for the bag methods
isEmpty
and
getCurrentSize
. Although these two methods are not in our first group of core methods,
they could have been. That is, we could have defined them earlier instead of writing stubs.
2.17
The method
getFrequencyOf
.
To count the number of times a given object occurs in a bag, we count
the number of times the object occurs in the array
bag
. Using a
for
loop to cycle through the array's
indices from 0 to
numberOfEntries -
1, we compare the given object to every object in the array.
