path: root/usth/ICT2.7/P4L5 Software Refactoring Subtitles/15 - Refactoring Demo - lang_en_vs4.srt

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So now we saw, this set of re-factoring's. They're nice, but

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how can we actually perform re-factoring's? In some cases you'll have to

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do it by hand. And you'll do it in that case in

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small steps, so that you can check at every step that you

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didn't introduce any area. But there's also many cases in which at

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least for the more standard re-factoring's, you can just apply, you can

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just use a tool that actually supports re-factoring. I'm going to show

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you how that works, into a specific ID, Eclipse through a demo.

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To show you how Eclipse, can help in performing

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re-factoring, in an automated way, I just opened the Eclipse

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editor and I maximized it. So that we can look

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at the code more clearly. And as you can see

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here, I have this class. It's called Re-factorable, it's a

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pretty indicative name. And what we're going to do, we're going to

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try to apply the extract method re-factoring to this class.

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And in particular, to parts of this print owing method.

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So this is a matter than will print owing's,

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as the name says. And it will do several things

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such as, for example, printing a banner first, then

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calculating the outstanding debts, and then printing some details. So

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the starting point for an extract method re-fractoring, is

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the identification of some cohesive code fragment. And here, for

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instance, we can see that, if we can see there,

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these three print statements. They are basically printing some banner,

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for the method. And I also put a comment here

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just to make that even more explicit. So this is a

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perfect case in which we might want to just extract

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this part, create an independent method, so that we can make

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the code more readable and maintainable. So I select, the

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part of the code, that I want to put in my

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method. I invoke the contextual menu, and as you can see

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there is a re-factor entry here. Here are some re-factoring's [UNKNOWN],

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re-factoring's that I can apply, and I'm going to select extract

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method. When I do that, Eclipse is going to ask me to

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specify a method name. I'll just call this one print

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banner. And as you can see, as soon as I do

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that, Eclipse will show me the preview, for the method

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that will be generated. I'm going to leave the access modifier. To

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public and I'm not going to change anything else. So,

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now when I click Ok. As you can see Eclipse modified

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my code so that now I have the Print Banner method

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down here that does exactly what that piece of code was doing

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before. And I just have an invocation of the Print Banner

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method, up here, where the code was before. And of course, this

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is something that we could have done by hand. It's pretty

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easy to do, but it's even easier, to do it using Eclipse's

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capabilities. And this will become even more apparent, when we consider slightly

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more complex case. So here, if we look at this piece of

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code for instance, we can that see this code

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prints some details, about the always. And the reason

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why this case is likely more complicated, is because

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this code needs to know about the value of outstanding.

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And whereas that underscore name, is a member of

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the class, and therefore will be available to the

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method. Outstanding is a locker variable, so a method

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different from print, oh it wouldn't know anything about outstanding.

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So let's see what happens when we try to apply

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a re-factoring for this code. So we go again here

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to the re-factor menu, we select extract method, we will

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pick a name again. So let's call it [SOUND] print details,

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since this is what the code does. And as you

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can see here, Eclipse was able to figure out, that outstanding

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has to be a parameter, of this method. So if

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you look at the signature here, this will be very clear.

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So outstanding has to be passed to the matter because

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it's a locker variable of the print owing method. so

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it will not be visible to the other methods otherwise.

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So since eclipse figured it out, all I have to do,

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is to press Ok. And at this point what I

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will have here is my new method, for in details

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that takes outstanding as a parameter. And does exactly what

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the code was doing before. And here, where the code was,

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I will have my print details invocation, with outstanding

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as a parameter. So now, let's continue to extract methods.

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And let's look at a even more complex case. which

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is, the one involving this piece of code. So this

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piece of code, as you can see, will calculate

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the value of the outstanding debt. Will calculate the owing's,

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and the way in which it does that, is by

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considering all the orders, that are part of this enumeration.

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That is the declared here, and it will

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compute for each one, of these orders, the amount,

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and then added to outstanding. So what is the

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additional complication here? Well, the additional complication here is

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that this code needs to know, not only

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about outstanding. It also needs to know, about this

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enumeration, because this one is also a local variable.

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And in addition to that, this code also has

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some side effects. So outstanding, is modified as a

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consequence of the execution of this code. So how can

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we do that in the extracted method? Well lets

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see what the clips will do and what the clips

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will suggest. It will try to again re-factor this

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code and extract the method. In this case as you

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can see. The clips does two things. First of all,

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it figures out as before, that there are some parameters,

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that are needed for this method to operate correctly. The

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enumeration e, as we said, and the outstanding variable. In

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addition, if you look at the method signature Eclipse will

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also figure out that this method has to return, a

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double value. So what does this value correspond to? This

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value corresponds to a new value of outstanding. So if

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we, give a name to this method, so we just

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use the name, [SOUND] that I put in the comment

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over there. We click Ok, and this will create

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a method by extracting the code. And here, where the

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method used to be, we will have that the

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value of outstanding is updated. Based on the return value

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of calculate outstanding. So in the end if we

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look at this code, you can see that if we

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just focus, on this code it's very easy to

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understand what it does. It prints the banner, it calculates

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an outstanding value, and then it prints some details. And

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in case we don't care, as I said before, about the

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details of what these methods do, we're done. And if we

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care about the details we can look at each matter individually.

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And get exactly the same information that we got before,

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in a sort of a separation of concerns kind of way,

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by focusing on one problem at a time. So now let

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me do one last thing. So let me modify the code,

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slightly. So i'm going to go back, to the version of

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the code before re-factoring. So this is what we had.

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And I'm going to add, an additional variable here, [SOUND] called count,

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which I initialize to zero. Here I'm going to increase, [SOUND]

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the value of count at every iteration. And

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finally, here I'm going to print out the value

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of count. Okay, now that I have this code up. So let's imagine that I

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want to, again as I did before, extract this matter. So, I'm going to

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give you a second. Have a look at this and see, if you see

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any problem with that. Feel free to stop the video, if you need more time.

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So the problem here is that I have two side effects.

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Both outstanding and count are modified. And therefore it's not really

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possible to extract this method, and preserve the semantics of this

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code. Let's see if Eclipse will be able to figure that out.

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And it does. If we try to extract the matter here,

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you'll tell us that's an ambiguous return value. The selected block

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contains more than one assignment to look at variables. And the

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affected variables are outstanding, just a Double and Count which is

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an integer. So it will refuse to extract the method. So

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at this point if we wanted to do that we have

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we'll have to do the re-factoring a different way, but I

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don't really want to get there. I want to conclude here,

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and I hope this this little demo helped you

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realize how useful it can be to use an

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id that supports re-factoring that can automate this important

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task. And I also encourage you to try to play

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with this, and try to use different re-factoring's, on

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your code. So as to get familiar with the kind

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of re-factoring's that are supported by the ID. And

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also with the re-factoring's themselves and how should be used.