The goal for this exercise is to continue exploring the concepts used in creating an array of object references.
What you need to do to prepare for this exercise:
This exercise does NOT deal with arrays of simple/primitive values (such as an array of integers).
Let’s say that we want to keep track of many Televisions. In order to do this, we’ll use two things:
A class that contains information about each Television, and
An array, which keeps track of our collection of televisions
For this exercise, you should continue to work with the TelevisionHandler and Television classes that were defined
in the previous exercises.
For this exercise, we will continue to write code the manipulates an array of object references.
What’s new about this exercise is that some of the object references may be null.
Implement the PrintArrayOfPossiblyNullTVs method in the TelevisionHandler class. The method needs
to do all of the following steps:
The first thing the method should do is create an array of 10 references to Television objects.
Next, write a for loop that
loops over the array, and checks each space in the array – if that slot is null, the
program should print out a message saying that “Slot X is null”, where
X is the space number. If the first element of the array is null, you
will see “Slot 0 is null”. What do you see when you run this code?
Include an easy to find comment explaining why you get the results you do, when you use a ‘printing loop’ on the array immediately after the array has been created.
Next, write code that allocates 4 Television objects, and stores those objects
into the array.Put one object into slot 0, another object into slot 1, another into slot
5, and the last into a slot 9.
For each TV, you should give it the brand “Brand X”, the size should be 42, and the
price should be 10 + the index in the array that the Television is being assigned
to.
Copy-and-paste the for loop that you wrote above, so that you can figure
out which slots in the array are null, and which aren’t. For slots that are null, continue
to print out the warning message. For any slots that aren’t null, call
the Print method on the object referred to by the slot.
Note that you can check for non-null slots either by using the else part of the existing
if statement, or else by asking if(array[slot] != null).
Include an easy to find comment explaining why you get the results you do, when you use a ‘printing loop’ on the array after you put 4 objects into the the array.
Next, add a loop that goes through the array. Each time it finds an array slot that is null,
it should create a new Television, and store that object into the empty
slot (in the slot with null in it). When this loop finishes running, every slot in the
array will be occupied.
For each TV, you should give it the brand “Brand X”, the size should be 42, and the
price should be 10 + the index in the array that the Television is being assigned
to.
Include an easy to find comment explaining why you get the results you do, when you use a ‘printing loop’ on the array after you’ve filled up the array with objects.
Lastly, copy-and-paste the for loop that you wrote above (in part b), so
that you can figure out which slots in the array are null, and which aren’t. Since there
should be no null slots, this means that this loop should print out 10 separate TVs.
NOTE: You must implement each loop separately! Even if you could combine the ‘print out the array that now contains 4 object references’ with the next loop (the one that fills in all null slots with new objects), you must write those two loops out separately. This will force you to repeatedly write out a loop that deals with an array with null values, which is good exercise, and good repetition!
OPTIONAL: Instead of just copy-and-pasting the ‘printing loop’ 3 times, create a method on the TelevisionHandler
class which will accept an array of Televisions as a parameter. It will go through
the array, and for each slot in the array, if the array slot is empty (if it’s null), it will
print out the message specified above. If the array slot is non-null (if it’s occupied), it will
call the Print method on the object referred to by that slot.
This is not required, but is good practice.
The Array_Of_Possibly_Null_Objects.RunExercise method is provided for you to test your implementation.
This will call the PrintArrayOfPossiblyNullTVs method in the TelevisionHandler class for you
(which is where your code should go).