WEBVTT

00:00:01.220 --> 00:00:02.580 align:middle
In this session,
I’d like to show you how

00:00:02.747 --> 00:00:05.220 align:middle
to use the debugger to program
differently.

00:00:05.760 --> 00:00:09.330 align:middle
We will implement again
the counter application

00:00:09.497 --> 00:00:14.190 align:middle
but in a different way, with a 
development flow more interactive.

00:00:16.940 --> 00:00:18.290 align:middle
First I will create

00:00:18.457 --> 00:00:20.840 align:middle
a new package with Counter, 
as previously.

00:00:26.050 --> 00:00:28.810 align:middle
I will also filter to have
less elements.

00:00:29.270 --> 00:00:33.240 align:middle
In MyCounter, I first 
define

00:00:34.960 --> 00:00:37.100 align:middle
a test, a test class.

00:00:37.267 --> 00:00:39.090 align:middle
Test classes inherit from TestCase.

00:00:40.260 --> 00:00:41.650 align:middle
I will call it Counter Test.

00:00:42.790 --> 00:00:44.870 align:middle
I will compile. I do it once
more in the menu and then

00:00:45.037 --> 00:00:46.340 align:middle
I do it with the comments.

00:00:46.507 --> 00:00:47.830 align:middle
It has created a test class.

00:00:48.260 --> 00:00:51.610 align:middle
In my test class, I write
a test method.

00:00:53.260 --> 00:00:56.150 align:middle
The test methods begin with test.

00:01:02.260 --> 00:01:04.160 align:middle
What do I do?

00:01:04.520 --> 00:01:07.820 align:middle
As previously, I define a local 
variable. In 

00:01:08.000 --> 00:01:12.570 align:middle
this local variable
I put an

00:01:12.737 --> 00:01:15.150 align:middle
object from the Counter class.

00:01:16.770 --> 00:01:21.130 align:middle
I initialise the Counter value
and

00:01:21.297 --> 00:01:25.500 align:middle
check that the Counter
has the right value.

00:01:31.450 --> 00:01:32.083 align:middle
I compile.

00:01:33.320 --> 00:01:36.070 align:middle
Now the system tells me:
“Warning! I don’t know

00:01:36.237 --> 00:01:38.250 align:middle
what Counter is.” It was already
indicated

00:01:38.417 --> 00:01:39.670 align:middle
with the italics here.

00:01:40.030 --> 00:01:42.460 align:middle
It proposes: “Do you want to define
a new class?

00:01:42.627 --> 00:01:44.040 align:middle
A new global or a class variable?

00:01:44.207 --> 00:01:45.000 align:middle
Here it is a new class.

00:01:45.137 --> 00:01:48.260 align:middle
It offers the class definition.

00:01:48.427 --> 00:01:50.790 align:middle
I say: “ok, it’s correct, it’s
in the right package, it inherits

00:01:50.957 --> 00:01:51.590 align:middle
from object, all right, do it.”

00:01:51.757 --> 00:01:55.160 align:middle
So it creates an empty class.

00:01:56.050 --> 00:01:58.520 align:middle
Now we are going to arrange this.

00:02:00.520 --> 00:02:04.260 align:middle
I can see that my Counter class
is empty.

00:02:04.610 --> 00:02:07.130 align:middle
If I execute my test, it is red.

00:02:07.297 --> 00:02:08.820 align:middle
Why is it red?

00:02:09.000 --> 00:02:09.860 align:middle
Because I have an error.

00:02:10.290 --> 00:02:11.760 align:middle
So how should I read this message?

00:02:11.927 --> 00:02:13.470 align:middle
Let’s take 2 minutes to do it.

00:02:14.630 --> 00:02:19.590 align:middle
The system says: “a Count message
has been sent to

00:02:19.757 --> 00:02:23.440 align:middle
an instance of the Counter class
and the corresponding

00:02:23.607 --> 00:02:28.240 align:middle
method wasn’t found.”
I’m going to look…

00:02:31.590 --> 00:02:32.360 align:middle
I open the debugger.

00:02:32.760 --> 00:02:36.050 align:middle
The debugger displays the execution
stack, so I can

00:02:36.217 --> 00:02:39.760 align:middle
see that a message hasn’t been 
understood.

00:02:39.927 --> 00:02:42.960 align:middle
And there it shows where the
message has been invoked.

00:02:43.760 --> 00:02:46.020 align:middle
I see that if I go there,
I can see the

00:02:46.187 --> 00:02:50.770 align:middle
system variables. If I look at C,
I can access

00:02:50.937 --> 00:02:55.010 align:middle
to the temporary C variable, which
is valued a Counter.

00:02:55.177 --> 00:02:56.920 align:middle
Anyway, if I write C class
for instance,

00:02:57.830 --> 00:03:00.730 align:middle
self class, it says it is 
the Counter class.

00:03:03.790 --> 00:03:08.230 align:middle
This is obvious. For the moment,
in my class, I don’t have any 

00:03:08.397 --> 00:03:12.620 align:middle
method. I will ask the system
to create one for me.

00:03:12.787 --> 00:03:13.590 align:middle
I do Create.

00:03:14.290 --> 00:03:15.630 align:middle
It proposes the classes.

00:03:15.797 --> 00:03:17.370 align:middle
I choose Counter class.

00:03:17.537 --> 00:03:18.670 align:middle
Can you create this?

00:03:18.837 --> 00:03:20.330 align:middle
Yes, in Accessing.

00:03:21.780 --> 00:03:23.620 align:middle
And finally what did he do?

00:03:25.930 --> 00:03:29.200 align:middle
It compiled automatically
a method with the right signature.

00:03:30.310 --> 00:03:31.850 align:middle
For the method body, it doesn’t 
know what to do,

00:03:32.017 --> 00:03:36.010 align:middle
so it uses
ShouldBeImplemented. What does it do?

00:03:36.177 --> 00:03:40.360 align:middle
It raises an exception at 
the execution and the system

00:03:40.527 --> 00:03:41.630 align:middle
execute again the method.

00:03:41.797 --> 00:03:44.140 align:middle
Now there is a new error and
I have to

00:03:44.570 --> 00:03:46.680 align:middle
implement the method body.

00:03:48.090 --> 00:03:49.950 align:middle
I know Count.
What am I going to do?

00:03:50.117 --> 00:03:53.020 align:middle
I want to assign this value to
an

00:03:53.187 --> 00:03:55.450 align:middle
instance variable. So here

00:03:58.180 --> 00:04:02.600 align:middle
it’s red, because for the moment 
my class doesn’t have this instance.

00:04:02.860 --> 00:04:04.170 align:middle
I compile.

00:04:05.130 --> 00:04:07.360 align:middle
The system proposes:
“Do you want a temporary variable

00:04:07.527 --> 00:04:09.140 align:middle
or an instance variable?”

00:04:09.307 --> 00:04:11.350 align:middle
I want an instance variable.

00:04:14.330 --> 00:04:19.040 align:middle
So I do this. If I look in my
class, I do have

00:04:19.207 --> 00:04:21.640 align:middle
a Count instance variable which
was created and

00:04:21.807 --> 00:04:26.650 align:middle
the method, the Setter, which

00:04:26.817 --> 00:04:27.450 align:middle
will set the value.

00:04:29.790 --> 00:04:31.390 align:middle
Once I’ve done this, I can tell
the debugger

00:04:31.557 --> 00:04:34.550 align:middle
to continue, Proceed means continue
the execution

00:04:34.717 --> 00:04:37.610 align:middle
as if nothing happened.

00:04:38.470 --> 00:04:39.103 align:middle
What happens?

00:04:39.270 --> 00:04:40.020 align:middle
There is still an error.

00:04:41.310 --> 00:04:44.600 align:middle
The system still says that 
there is an instance

00:04:44.767 --> 00:04:47.000 align:middle
of Counter class which received
the count message and that

00:04:47.167 --> 00:04:50.360 align:middle
it hasn’t found the appropriate 
method. This is normal because 

00:04:50.527 --> 00:04:54.250 align:middle
C does have 7

00:04:55.680 --> 00:05:00.420 align:middle
in its Counter, in its count variable, 
however

00:05:00.587 --> 00:05:01.850 align:middle
the count method doesn’t exist.

00:05:02.250 --> 00:05:03.080 align:middle
I’m gonna create it.

00:05:03.247 --> 00:05:05.360 align:middle
I will do Create. In which class?

00:05:05.527 --> 00:05:09.000 align:middle
Still the Counter class, in 
the accessing protocol,

00:05:09.460 --> 00:05:14.310 align:middle
because it’s an accessor.
And there you

00:05:14.477 --> 00:05:18.260 align:middle
see that the system is smarter.

00:05:18.427 --> 00:05:21.680 align:middle
It noticed that there was an
instance variable named

00:05:21.847 --> 00:05:26.000 align:middle
count, and it wants to define a 
method named count,

00:05:27.120 --> 00:05:29.240 align:middle
so let’s propose it an accessor.

00:05:29.410 --> 00:05:30.140 align:middle
That’s what I wanted.

00:05:30.307 --> 00:05:31.050 align:middle
So now I can Proceed.

00:05:32.440 --> 00:05:33.350 align:middle
What do I see?

00:05:33.517 --> 00:05:37.750 align:middle
My test is green. I have a test 
green and

00:05:37.917 --> 00:05:42.050 align:middle
2 methods have been created 
in my class.

00:05:44.240 --> 00:05:45.470 align:middle
Now I will do the same
for increment.

00:05:49.640 --> 00:05:51.100 align:middle
In fact, I am

00:05:51.267 --> 00:05:54.490 align:middle
specifying what the method 
has to do

00:05:54.657 --> 00:05:56.240 align:middle
and checking that it does do it. 

00:05:58.360 --> 00:06:03.090 align:middle
So there I must have 9,
I compile, I execute.

00:06:03.300 --> 00:06:07.730 align:middle
And the system tells me that
it doesn’t know the increment method.

00:06:07.897 --> 00:06:12.490 align:middle
Yes, it’s normal. I do Create,
here in operation.

00:06:15.960 --> 00:06:19.950 align:middle
If I look at increment,
I can do count.

00:06:20.750 --> 00:06:25.230 align:middle
= count + 1. I compile.

00:06:27.080 --> 00:06:29.570 align:middle
Proceed. I do have my test.

00:06:30.370 --> 00:06:31.760 align:middle
While I’m at it, I create decrement.

00:06:31.927 --> 00:06:36.050 align:middle
The idea is for you to do it, 
to practice it.

00:06:39.520 --> 00:06:43.120 align:middle
So here it will be 5.
I define my test.

00:06:45.460 --> 00:06:46.750 align:middle
I create my method.

00:06:51.480 --> 00:06:55.000 align:middle
OK. So now you know, 
count: = count,

00:07:00.330 --> 00:07:01.660 align:middle
I compile in the debugger.

00:07:01.827 --> 00:07:05.640 align:middle
I click on Proceed. And my 
tests are green.

00:07:05.807 --> 00:07:10.060 align:middle
Now my class has 2 operations:
increment and decrement.

00:07:10.420 --> 00:07:11.770 align:middle
It’s time to save,
for example.

00:07:12.010 --> 00:07:14.500 align:middle
I’m going to save like I’ve
shown you before.

00:07:15.280 --> 00:07:19.180 align:middle
I click on Save, I save and

00:07:20.040 --> 00:07:20.760 align:middle
here I write "with

00:07:25.740 --> 00:07:29.430 align:middle
accessors and decrement
increment covered by green tests".

00:07:29.597 --> 00:07:34.000 align:middle
So here it is! I’ve saved that.

00:07:47.250 --> 00:07:47.883 align:middle
Allright.

00:07:49.100 --> 00:07:52.860 align:middle
The important thing to remember
in this session is that 

00:07:53.390 --> 00:07:58.250 align:middle
the debugger gives access to
the object’s

00:07:58.417 --> 00:08:02.340 align:middle
state, it places you in the 
right call context and

00:08:02.507 --> 00:08:04.460 align:middle
enables you to use the call context 
to have all the necessary

00:08:04.627 --> 00:08:07.390 align:middle
information to write
your code. 

00:08:07.557 --> 00:08:08.690 align:middle
And this is really very,
very powerful.