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diff --git a/usth/ICT2.7/P4L5 Software Refactoring Subtitles/15 - Refactoring Demo - lang_en_vs4.srt b/usth/ICT2.7/P4L5 Software Refactoring Subtitles/15 - Refactoring Demo - lang_en_vs4.srt new file mode 100644 index 0000000..0559c88 --- /dev/null +++ b/usth/ICT2.7/P4L5 Software Refactoring Subtitles/15 - Refactoring Demo - lang_en_vs4.srt @@ -0,0 +1,599 @@ +1 +00:00:00,090 --> 00:00:03,110 +So now we saw, this set of re-factoring's. They're nice, but + +2 +00:00:03,110 --> 00:00:06,260 +how can we actually perform re-factoring's? In some cases you'll have to + +3 +00:00:06,260 --> 00:00:08,430 +do it by hand. And you'll do it in that case in + +4 +00:00:08,430 --> 00:00:10,880 +small steps, so that you can check at every step that you + +5 +00:00:10,880 --> 00:00:14,180 +didn't introduce any area. But there's also many cases in which at + +6 +00:00:14,180 --> 00:00:17,640 +least for the more standard re-factoring's, you can just apply, you can + +7 +00:00:17,640 --> 00:00:21,530 +just use a tool that actually supports re-factoring. I'm going to show + +8 +00:00:21,530 --> 00:00:24,550 +you how that works, into a specific ID, Eclipse through a demo. + +9 +00:00:26,120 --> 00:00:28,425 +To show you how Eclipse, can help in performing + +10 +00:00:28,425 --> 00:00:31,880 +re-factoring, in an automated way, I just opened the Eclipse + +11 +00:00:31,880 --> 00:00:35,050 +editor and I maximized it. So that we can look + +12 +00:00:35,050 --> 00:00:36,810 +at the code more clearly. And as you can see + +13 +00:00:36,810 --> 00:00:39,551 +here, I have this class. It's called Re-factorable, it's a + +14 +00:00:39,551 --> 00:00:43,550 +pretty indicative name. And what we're going to do, we're going to + +15 +00:00:43,550 --> 00:00:47,840 +try to apply the extract method re-factoring to this class. + +16 +00:00:47,840 --> 00:00:51,060 +And in particular, to parts of this print owing method. + +17 +00:00:51,060 --> 00:00:54,090 +So this is a matter than will print owing's, + +18 +00:00:54,090 --> 00:00:56,160 +as the name says. And it will do several things + +19 +00:00:56,160 --> 00:00:59,180 +such as, for example, printing a banner first, then + +20 +00:00:59,180 --> 00:01:03,650 +calculating the outstanding debts, and then printing some details. So + +21 +00:01:03,650 --> 00:01:06,980 +the starting point for an extract method re-fractoring, is + +22 +00:01:06,980 --> 00:01:10,650 +the identification of some cohesive code fragment. And here, for + +23 +00:01:10,650 --> 00:01:12,970 +instance, we can see that, if we can see there, + +24 +00:01:12,970 --> 00:01:16,350 +these three print statements. They are basically printing some banner, + +25 +00:01:16,350 --> 00:01:18,530 +for the method. And I also put a comment here + +26 +00:01:18,530 --> 00:01:21,160 +just to make that even more explicit. So this is a + +27 +00:01:21,160 --> 00:01:23,970 +perfect case in which we might want to just extract + +28 +00:01:23,970 --> 00:01:27,220 +this part, create an independent method, so that we can make + +29 +00:01:27,220 --> 00:01:31,410 +the code more readable and maintainable. So I select, the + +30 +00:01:31,410 --> 00:01:33,320 +part of the code, that I want to put in my + +31 +00:01:33,320 --> 00:01:37,080 +method. I invoke the contextual menu, and as you can see + +32 +00:01:37,080 --> 00:01:41,287 +there is a re-factor entry here. Here are some re-factoring's [UNKNOWN], + +33 +00:01:41,287 --> 00:01:45,039 +re-factoring's that I can apply, and I'm going to select extract + +34 +00:01:45,039 --> 00:01:48,120 +method. When I do that, Eclipse is going to ask me to + +35 +00:01:48,120 --> 00:01:51,610 +specify a method name. I'll just call this one print + +36 +00:01:51,610 --> 00:01:54,260 +banner. And as you can see, as soon as I do + +37 +00:01:54,260 --> 00:01:57,310 +that, Eclipse will show me the preview, for the method + +38 +00:01:57,310 --> 00:02:01,010 +that will be generated. I'm going to leave the access modifier. To + +39 +00:02:01,010 --> 00:02:03,290 +public and I'm not going to change anything else. So, + +40 +00:02:03,290 --> 00:02:07,760 +now when I click Ok. As you can see Eclipse modified + +41 +00:02:07,760 --> 00:02:10,669 +my code so that now I have the Print Banner method + +42 +00:02:10,669 --> 00:02:14,050 +down here that does exactly what that piece of code was doing + +43 +00:02:14,050 --> 00:02:16,090 +before. And I just have an invocation of the Print Banner + +44 +00:02:16,090 --> 00:02:19,440 +method, up here, where the code was before. And of course, this + +45 +00:02:19,440 --> 00:02:21,830 +is something that we could have done by hand. It's pretty + +46 +00:02:21,830 --> 00:02:25,480 +easy to do, but it's even easier, to do it using Eclipse's + +47 +00:02:25,480 --> 00:02:29,040 +capabilities. And this will become even more apparent, when we consider slightly + +48 +00:02:29,040 --> 00:02:32,866 +more complex case. So here, if we look at this piece of + +49 +00:02:32,866 --> 00:02:35,234 +code for instance, we can that see this code + +50 +00:02:35,234 --> 00:02:38,264 +prints some details, about the always. And the reason + +51 +00:02:38,264 --> 00:02:41,351 +why this case is likely more complicated, is because + +52 +00:02:41,351 --> 00:02:45,210 +this code needs to know about the value of outstanding. + +53 +00:02:45,210 --> 00:02:49,130 +And whereas that underscore name, is a member of + +54 +00:02:49,130 --> 00:02:51,150 +the class, and therefore will be available to the + +55 +00:02:51,150 --> 00:02:55,110 +method. Outstanding is a locker variable, so a method + +56 +00:02:55,110 --> 00:02:58,310 +different from print, oh it wouldn't know anything about outstanding. + +57 +00:02:58,310 --> 00:03:00,070 +So let's see what happens when we try to apply + +58 +00:03:00,070 --> 00:03:03,460 +a re-factoring for this code. So we go again here + +59 +00:03:03,460 --> 00:03:06,410 +to the re-factor menu, we select extract method, we will + +60 +00:03:06,410 --> 00:03:10,080 +pick a name again. So let's call it [SOUND] print details, + +61 +00:03:10,080 --> 00:03:12,660 +since this is what the code does. And as you + +62 +00:03:12,660 --> 00:03:17,270 +can see here, Eclipse was able to figure out, that outstanding + +63 +00:03:17,270 --> 00:03:20,290 +has to be a parameter, of this method. So if + +64 +00:03:20,290 --> 00:03:23,340 +you look at the signature here, this will be very clear. + +65 +00:03:23,340 --> 00:03:26,270 +So outstanding has to be passed to the matter because + +66 +00:03:26,270 --> 00:03:29,230 +it's a locker variable of the print owing method. so + +67 +00:03:29,230 --> 00:03:32,600 +it will not be visible to the other methods otherwise. + +68 +00:03:32,600 --> 00:03:34,990 +So since eclipse figured it out, all I have to do, + +69 +00:03:34,990 --> 00:03:37,630 +is to press Ok. And at this point what I + +70 +00:03:37,630 --> 00:03:41,280 +will have here is my new method, for in details + +71 +00:03:41,280 --> 00:03:45,140 +that takes outstanding as a parameter. And does exactly what + +72 +00:03:45,140 --> 00:03:48,880 +the code was doing before. And here, where the code was, + +73 +00:03:48,880 --> 00:03:51,630 +I will have my print details invocation, with outstanding + +74 +00:03:51,630 --> 00:03:54,930 +as a parameter. So now, let's continue to extract methods. + +75 +00:03:54,930 --> 00:03:58,470 +And let's look at a even more complex case. which + +76 +00:03:58,470 --> 00:04:01,550 +is, the one involving this piece of code. So this + +77 +00:04:01,550 --> 00:04:03,900 +piece of code, as you can see, will calculate + +78 +00:04:03,900 --> 00:04:07,820 +the value of the outstanding debt. Will calculate the owing's, + +79 +00:04:07,820 --> 00:04:09,600 +and the way in which it does that, is by + +80 +00:04:09,600 --> 00:04:14,080 +considering all the orders, that are part of this enumeration. + +81 +00:04:14,080 --> 00:04:16,519 +That is the declared here, and it will + +82 +00:04:16,519 --> 00:04:20,769 +compute for each one, of these orders, the amount, + +83 +00:04:20,769 --> 00:04:23,520 +and then added to outstanding. So what is the + +84 +00:04:23,520 --> 00:04:26,160 +additional complication here? Well, the additional complication here is + +85 +00:04:26,160 --> 00:04:29,520 +that this code needs to know, not only + +86 +00:04:29,520 --> 00:04:33,220 +about outstanding. It also needs to know, about this + +87 +00:04:33,220 --> 00:04:36,160 +enumeration, because this one is also a local variable. + +88 +00:04:36,160 --> 00:04:39,140 +And in addition to that, this code also has + +89 +00:04:39,140 --> 00:04:43,280 +some side effects. So outstanding, is modified as a + +90 +00:04:43,280 --> 00:04:46,600 +consequence of the execution of this code. So how can + +91 +00:04:46,600 --> 00:04:49,120 +we do that in the extracted method? Well lets + +92 +00:04:49,120 --> 00:04:51,000 +see what the clips will do and what the clips + +93 +00:04:51,000 --> 00:04:53,950 +will suggest. It will try to again re-factor this + +94 +00:04:53,950 --> 00:04:58,030 +code and extract the method. In this case as you + +95 +00:04:58,030 --> 00:05:01,160 +can see. The clips does two things. First of all, + +96 +00:05:01,160 --> 00:05:04,180 +it figures out as before, that there are some parameters, + +97 +00:05:04,180 --> 00:05:07,650 +that are needed for this method to operate correctly. The + +98 +00:05:07,650 --> 00:05:11,600 +enumeration e, as we said, and the outstanding variable. In + +99 +00:05:11,600 --> 00:05:14,880 +addition, if you look at the method signature Eclipse will + +100 +00:05:14,880 --> 00:05:17,490 +also figure out that this method has to return, a + +101 +00:05:17,490 --> 00:05:21,530 +double value. So what does this value correspond to? This + +102 +00:05:21,530 --> 00:05:24,700 +value corresponds to a new value of outstanding. So if + +103 +00:05:24,700 --> 00:05:27,490 +we, give a name to this method, so we just + +104 +00:05:27,490 --> 00:05:29,620 +use the name, [SOUND] that I put in the comment + +105 +00:05:29,620 --> 00:05:33,510 +over there. We click Ok, and this will create + +106 +00:05:33,510 --> 00:05:36,560 +a method by extracting the code. And here, where the + +107 +00:05:36,560 --> 00:05:39,100 +method used to be, we will have that the + +108 +00:05:39,100 --> 00:05:43,169 +value of outstanding is updated. Based on the return value + +109 +00:05:43,169 --> 00:05:46,260 +of calculate outstanding. So in the end if we + +110 +00:05:46,260 --> 00:05:48,730 +look at this code, you can see that if we + +111 +00:05:48,730 --> 00:05:51,980 +just focus, on this code it's very easy to + +112 +00:05:51,980 --> 00:05:55,150 +understand what it does. It prints the banner, it calculates + +113 +00:05:55,150 --> 00:05:59,180 +an outstanding value, and then it prints some details. And + +114 +00:05:59,180 --> 00:06:01,520 +in case we don't care, as I said before, about the + +115 +00:06:01,520 --> 00:06:04,840 +details of what these methods do, we're done. And if we + +116 +00:06:04,840 --> 00:06:07,740 +care about the details we can look at each matter individually. + +117 +00:06:07,740 --> 00:06:10,580 +And get exactly the same information that we got before, + +118 +00:06:10,580 --> 00:06:13,650 +in a sort of a separation of concerns kind of way, + +119 +00:06:13,650 --> 00:06:16,420 +by focusing on one problem at a time. So now let + +120 +00:06:16,420 --> 00:06:19,345 +me do one last thing. So let me modify the code, + +121 +00:06:19,345 --> 00:06:23,170 +slightly. So i'm going to go back, to the version of + +122 +00:06:23,170 --> 00:06:25,610 +the code before re-factoring. So this is what we had. + +123 +00:06:25,610 --> 00:06:32,480 +And I'm going to add, an additional variable here, [SOUND] called count, + +124 +00:06:32,480 --> 00:06:38,870 +which I initialize to zero. Here I'm going to increase, [SOUND] + +125 +00:06:38,870 --> 00:06:41,360 +the value of count at every iteration. And + +126 +00:06:41,360 --> 00:06:44,570 +finally, here I'm going to print out the value + +127 +00:06:44,570 --> 00:06:50,130 +of count. Okay, now that I have this code up. So let's imagine that I + +128 +00:06:50,130 --> 00:06:55,665 +want to, again as I did before, extract this matter. So, I'm going to + +129 +00:06:55,665 --> 00:06:58,430 +give you a second. Have a look at this and see, if you see + +130 +00:06:58,430 --> 00:07:02,170 +any problem with that. Feel free to stop the video, if you need more time. + +131 +00:07:07,350 --> 00:07:11,440 +So the problem here is that I have two side effects. + +132 +00:07:11,440 --> 00:07:14,820 +Both outstanding and count are modified. And therefore it's not really + +133 +00:07:14,820 --> 00:07:19,600 +possible to extract this method, and preserve the semantics of this + +134 +00:07:19,600 --> 00:07:23,260 +code. Let's see if Eclipse will be able to figure that out. + +135 +00:07:26,130 --> 00:07:28,950 +And it does. If we try to extract the matter here, + +136 +00:07:28,950 --> 00:07:32,250 +you'll tell us that's an ambiguous return value. The selected block + +137 +00:07:32,250 --> 00:07:35,800 +contains more than one assignment to look at variables. And the + +138 +00:07:35,800 --> 00:07:40,170 +affected variables are outstanding, just a Double and Count which is + +139 +00:07:40,170 --> 00:07:44,780 +an integer. So it will refuse to extract the method. So + +140 +00:07:44,780 --> 00:07:46,470 +at this point if we wanted to do that we have + +141 +00:07:46,470 --> 00:07:48,650 +we'll have to do the re-factoring a different way, but I + +142 +00:07:48,650 --> 00:07:51,110 +don't really want to get there. I want to conclude here, + +143 +00:07:51,110 --> 00:07:53,440 +and I hope this this little demo helped you + +144 +00:07:53,440 --> 00:07:55,310 +realize how useful it can be to use an + +145 +00:07:55,310 --> 00:07:58,270 +id that supports re-factoring that can automate this important + +146 +00:07:58,270 --> 00:08:00,160 +task. And I also encourage you to try to play + +147 +00:08:00,160 --> 00:08:03,170 +with this, and try to use different re-factoring's, on + +148 +00:08:03,170 --> 00:08:05,480 +your code. So as to get familiar with the kind + +149 +00:08:05,480 --> 00:08:08,060 +of re-factoring's that are supported by the ID. And + +150 +00:08:08,060 --> 00:08:10,800 +also with the re-factoring's themselves and how should be used. |