Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll

Java Objects

Well done!

You have completed Java Objects!

Sign up for Treehouse Back to Library
Preview
Video Player
00:00
00:00
00:00
  1. 2x 2x
  2. 1.75x 1.75x
  3. 1.5x 1.5x
  4. 1.25x 1.25x
  5. 1.1x 1.1x
  6. 1x 1x
  7. 0.75x 0.75x
  8. 0.5x 0.5x
Use Up/Down Arrow keys to increase or decrease volume.

Abstraction at Play

8:34 with Craig Dennis

You can create computed properties that help to abstract away how your object is working internally.

One nice thing that we can do as proactive developers, 0:01
is to add methods that provide functionality or 0:04
information that we expect might be a common question about our object. 0:06
By gathering common functionality, we can help to reduce code duplication for 0:11
ourselves, and for consumers of our code. 0:15
We can use methods to provide conceptual state 0:18
about our instance that other developers, and 0:21
us included, don't actually need to worry about when using the object. 0:23
So more specifically, if we try and 0:27
visualize how people are going to use our Pez dispenser object, 0:30
one common question I could foresee happening would be, is this thing empty? 0:33
Now I'll check, and I'll say no, because there is indeed some in there. 0:38
Because that is probably going to be asked of the object, 0:41
we should probably provide the answer to that common question to our users. 0:44
What we don't want to do is force the user to understand how our 0:49
object works internally. 0:52
We just want them to be able to ask, is it empty? 0:54
And our object can respond with yep or nope. 0:57
So let's do that. 0:59
Let's create that method but before we create that method, let's jump back into 1:01
Jshell and add some more powerful tools to the expressions we write. 1:04
Okay, so go ahead and open up JShell, and let's walk through a couple things. 1:09
So first, we know how to see if a number is greater or 1:13
less than another number, right? 1:18
So we can do that, we can say 5 is greater than 4, and we use the sign like that. 1:19
And we can also say that 6 is less than 7. 1:24
Now one thing that might not be too clear is equality of numbers. 1:28
So, let's go ahead and let's say that five is equal to five. 1:32
Now, there's a little thing that you need to be careful of here. 1:37
When you're testing equality, you need to use double equals. 1:40
So you say equal equal five. 1:43
And that is because, as you know, 1:45
the equal sign has already been used for variable assignments, like this, right. 1:48
So, if we said the age is equal to 19, 1:54
that's how we set the age for variable assignment. 1:57
But, if we wanted to check the age, we would need to do double equals. 2:00
Otherwise, we'd just be overwriting it each time. 2:03
Common mistake, pay attention to that one. 2:05
Just want to make sure that was out there, so we have this now we can check equality. 2:08
So, we should be able to make the is empty method, right? 2:12
Since we don't want anybody else to have to write the double equals code 2:15
double equals zero. 2:19
We definitely know that we want the method to be public, 2:20
because we want people to use this. 2:24
So we'll say public, and next we want it to return a true or 2:25
false value, which means we'll be expecting a boolean. 2:30
Booleans are a special case, when you name property methods. 2:34
So the standard, you know, for getters like we have before, we have a get. 2:38
If you have one that is a boolean, you want it to be is, 2:42
because it kind of reads better that way, and you'll see here a second. 2:45
So we'll say IS empty, right? 2:48
Okay, so we'll do that, we'll open it, we'll close it. 2:52
So, what should we do? 2:55
Let's think, we could create a brand new private boolean field and 2:57
store it up here, right? 3:01
But with our current code, whenever somebody does this fill method here, 3:02
we'd have to set it to true or false. 3:06
And it seems like we'd have to like always keep state in that way. 3:09
It seems awfully brittle doesn't it? 3:12
It's a whole lot to remember and if we forget, 3:14
it could actually end up doing more harm than good. 3:16
So a nice thing about objects is that we can actually compute our property. 3:19
Now, we know how to do it, right. 3:24
We just talked about it. 3:26
If the Pez count is zero, then it's empty. 3:27
So we could do something like this, right. 3:31
So this code is going to run. 3:33
So we can make a new variable here, 3:34
and we'll name it something different, is actually empty. 3:36
And we'll do just like we did down here in the Jshell. 3:40
We'll say if the Pez count is double equal to zero, 3:43
the Pez count is equal to zero, then it is empty, right? 3:48
So, we'll return this variable here is actually empty. 3:51
That works. 3:56
But wait a second. 3:57
Notice how we're creating a variable here, 3:59
in the just immediately returning its value. 4:02
Well, we can actually clean this up. 4:04
We can actually return this expression. 4:06
So I'm gonna copy that and I'm going to paste it here. 4:07
And then I want to get rid of this line here and so 4:11
it just has this has pezCount is double equal to zero. 4:13
Because this is going to return a true, and then our method is going to return 4:16
that value and it's gonna be a boolean, or a true or a false. 4:19
Cool. So I have saved that and 4:23
it looks like it's working. 4:24
I wanna go ahead. 4:25
Let's make sure it is. 4:26
So we're gonna explore. 4:27
We'll open PezDispenser to that Java. 4:29
We'll make a new PezDispenser. 4:34
You know use that poor naming convention there of PD, we'll say new PezDispenser. 4:37
Cool so we've got a new one, 4:45
I'm going to press control L, get a new screen here, all right. 4:48
So it was just created. 4:51
So isEmpty best return true, right? 4:53
Because the pezCount comes in, it's set to zero. 4:55
So let's do that. 4:58
Cool, so it is empty, and then, if we fill it. 5:01
So, that's going to set this max_pez on the pezCount. 5:07
So now the pezCount should be max_pez, which is 12. 5:10
So lets see if pd.isEmpty, and it should return false. 5:13
Cool. It's working. 5:19
So since we've explored, and we know that it works, 5:21
let's write out some code over here in our example class that uses it. 5:24
So, let's test out some if statements. 5:28
Now remember, if statements allow us to run certain code 5:33
only if certain expressions are true. 5:35
So, let's just play with it a little bit here. 5:37
We'll say, 5:40
if dispenser is empty, 5:43
then we'll print out 5:48
dispenser is empty. 5:52
So here, let's show that the dispenser is no longer empty. 6:02
So, we want to do the inverse of empty. 6:06
Now, we don't need to write that method, because we have the capability to do that. 6:09
We can use the not symbol. 6:13
Not inverts the expression, or negates the value it follows. 6:15
So, we do something like this. 6:18
So if an exclamation point is not, 6:20
if not the dispenser is empty, 6:27
[SOUND] we'll print out, 6:33
Dispenser is full. 6:38
Cool, so let's drop out of JShell, 6:42
and now if we compile and run this, here we go. 6:45
So we see the dispenser is empty and 6:50
we know that that happened because this will only print out if it was empty. 6:51
And then, this will only print out if it's full, and on both sides it prints out. 6:55
We did it. 6:59
Awesome, way to be proactive. 7:01
Did you see how by exposing that most likely common request about 7:03
the state of our object, we have avoided the need for us and 7:07
other developers to write that exact same equality check code again and again? 7:10
We encapsulated how the check happens and 7:14
we have avoided having to actually show how many Pez were available. 7:17
Chalk that up as another added benefit to using objects. 7:21
If you look at the code in example dot Java, 7:25
you see how much it reads almost like English. 7:27
If the dispenser is empty, fill it. 7:30
In my opinion, this is the key to being a successful programmer. 7:33
The more you can write your code so that someone can just look at it and 7:37
understand what it's doing, the more you are mastering the art of programming. 7:40
This will become increasingly more natural the more you practice. 7:44
And the more you get to know your object. 7:48
And you witness how it's being used, the more you'll be able to make 7:50
sure that the methods you provide are clear and readable. 7:53
The other important thing that I'd really like to emphasize here is this. 7:56
Try not to take offense if someone doesn't understand what your code is 8:00
trying to accomplish. 8:03
Always try to take that as an opportunity to further 8:05
improve your code for readability. 8:08
Now, chances are, 8:10
if that person didn't understand your code, others might have the same problem. 8:11
After all, the main reason that we're writing code is to express our thoughts. 8:15
We definitely want them to be understood. 8:19
The more legible your code is, the more it can be reused and maintained. 8:21
Always strive for clarity. 8:25
The time spent is well worth it, I promise. 8:27
All right, so after this next exercise, 8:30
let's start getting some candy out of this. 8:31