1 00:00:00,900 --> 00:00:05,090 Let's not look at a very important I know very interesting topic. 2 00:00:05,520 --> 00:00:13,020 It's about losing eclipses debugger as the name suggests a debugger is a tool that aids in application 3 00:00:13,020 --> 00:00:14,140 debugging. 4 00:00:14,250 --> 00:00:19,890 That is if there is a bug which is nothing but a defect in your application then you would debug it 5 00:00:19,900 --> 00:00:20,290 . 6 00:00:20,670 --> 00:00:26,370 So if you see any defects in your application then you can run the debugger to investigate the issue 7 00:00:27,000 --> 00:00:32,130 and then identify the exact problem area and then subsequently fix it. 8 00:00:32,250 --> 00:00:39,540 The application will be run by more when you're running the debugger debugger is also useful in understanding 9 00:00:39,540 --> 00:00:41,120 the program flow. 10 00:00:41,190 --> 00:00:46,500 So if you're looking at some code that you are not familiar with then you can use a debugger to get 11 00:00:46,500 --> 00:00:49,670 a good understanding of how the program works. 12 00:00:49,680 --> 00:00:55,290 That's a really effective way to understand code written by someone else in this lesson we will learn 13 00:00:55,290 --> 00:00:58,470 how to use a debugger effectively. 14 00:00:58,830 --> 00:01:01,760 So let's get started now. 15 00:01:02,020 --> 00:01:03,900 Good debugging application. 16 00:01:03,990 --> 00:01:10,740 The first thing you would do is set one or more breakpoints a break point is the place with the debugger 17 00:01:10,740 --> 00:01:11,980 with boss. 18 00:01:12,000 --> 00:01:17,770 So when you start a debugger it would run the application on would stop at the first break point. 19 00:01:18,240 --> 00:01:23,000 So a break point is essentially the point where you want to investigate the code. 20 00:01:23,520 --> 00:01:28,370 So let's just go ahead and place on a breakpoint in the student test class. 21 00:01:28,470 --> 00:01:33,300 So here we are in the Student class and we are iterating over all the students and printing the name 22 00:01:33,300 --> 00:01:34,160 and gender. 23 00:01:34,470 --> 00:01:39,170 So let's just go ahead and place our break for point here in line 35. 24 00:01:39,540 --> 00:01:42,160 And all we need to do is just double click here. 25 00:01:42,360 --> 00:01:43,850 And that's a break point. 26 00:01:43,860 --> 00:01:46,840 Now if you want to remove it just double click again. 27 00:01:47,100 --> 00:01:47,510 OK. 28 00:01:47,670 --> 00:01:53,940 So let's just go ahead double quick here and to start the debugger all we need to do is press this button 29 00:01:53,940 --> 00:02:02,310 over here ARE WE CAN DO IT RIGHT CLICK HERE answered run debug ass java application. 30 00:02:02,310 --> 00:02:07,120 Now if you do run as to our application it would simply run the application without the debugger. 31 00:02:07,500 --> 00:02:10,140 OK so let's just go here. 32 00:02:10,560 --> 00:02:13,930 Press this button here. 33 00:02:14,070 --> 00:02:21,360 Now what happened was earlier we were in Djala perspective now because we have started a debug session 34 00:02:21,570 --> 00:02:23,240 it opened a debug perspective. 35 00:02:23,250 --> 00:02:25,480 OK so we are here in the book Wisbech. 36 00:02:25,740 --> 00:02:32,980 Sometimes this would invoke a pop up on you with a dialog and you would have to hit okay for that. 37 00:02:33,390 --> 00:02:36,480 And if that happens or you can go ahead and do it. 38 00:02:36,480 --> 00:02:37,160 OK. 39 00:02:37,440 --> 00:02:40,020 So here we are in debug perspective. 40 00:02:40,150 --> 00:02:41,930 And it shows different views here. 41 00:02:41,970 --> 00:02:44,950 So this is the debug view here. 42 00:02:45,150 --> 00:02:46,530 This is a debug view. 43 00:02:46,860 --> 00:02:50,010 And here are sites variables view. 44 00:02:50,030 --> 00:02:51,840 I will get back to that later. 45 00:02:52,070 --> 00:02:53,810 And here is the editor. 46 00:02:54,220 --> 00:02:58,820 And here is a concern as application is running we will see the output here. 47 00:02:58,830 --> 00:03:01,770 So let's just go ahead and close this outline. 48 00:03:01,770 --> 00:03:06,240 So the debugger has started on it has stopped at the first big point here. 49 00:03:06,420 --> 00:03:07,900 So that's like totally fine. 50 00:03:08,240 --> 00:03:13,570 And here within the debug view what this means is it's telling. 51 00:03:13,580 --> 00:03:19,920 This is called It's a stack frame and it is telling that we are inside the main method at line 35 and 52 00:03:19,920 --> 00:03:24,850 these are all the local variables of attend the main matter first. 53 00:03:25,020 --> 00:03:28,910 I would like to talk about is about these three features here. 54 00:03:28,950 --> 00:03:33,070 So let's just go and then this is called a step into step over step here. 55 00:03:33,070 --> 00:03:40,350 And so let's just begin with this step over which has a shortcut of F 6 also and what it means is what 56 00:03:40,440 --> 00:03:43,290 exactly the current line in the statement. 57 00:03:43,470 --> 00:03:46,210 And it would more move to the next statement. 58 00:03:46,320 --> 00:03:49,990 OK so let's just do that. 59 00:03:50,040 --> 00:03:55,620 So as you can see we are at line 36 now and even here it has changed to 36. 60 00:03:55,620 --> 00:03:58,100 Now let's look at the variables here. 61 00:03:58,170 --> 00:04:00,380 So we just executed this here. 62 00:04:00,510 --> 00:04:03,900 This line the statement in line 35 on its name. 63 00:04:04,110 --> 00:04:10,530 And if you see a free highlighted here where here Howard the name variable we can see that it is the 64 00:04:10,530 --> 00:04:12,130 name is initialized to John. 65 00:04:12,240 --> 00:04:12,960 OK. 66 00:04:12,960 --> 00:04:19,030 So this is a student and you can see the same output here also name value is Jo-Anne. 67 00:04:19,190 --> 00:04:19,870 OK. 68 00:04:19,950 --> 00:04:23,040 Now let's step over once again. 69 00:04:23,040 --> 00:04:29,040 So we don't we have just executed the second statement and gender is male ungenerous male here so new 70 00:04:29,040 --> 00:04:30,390 variable got created. 71 00:04:30,870 --> 00:04:32,830 And here is a method right. 72 00:04:32,850 --> 00:04:37,860 So if we want to investigate the matter what we can do is we can step into. 73 00:04:37,890 --> 00:04:41,510 Which means that we are telling the debugger to step into that matter. 74 00:04:41,580 --> 00:04:42,830 So let's just do that. 75 00:04:44,890 --> 00:04:51,010 Now here we are in the first statement of the method and you can see that this has changed do you know 76 00:04:51,070 --> 00:04:57,040 the main method the stack frame corresponding to main method of went down and then we have a new stack 77 00:04:57,040 --> 00:04:59,150 frame corresponding to the numerator. 78 00:04:59,170 --> 00:05:02,230 So it's here right now and we are at line 48. 79 00:05:02,230 --> 00:05:05,360 And these are the variables corresponding to the numerator. 80 00:05:05,540 --> 00:05:06,150 OK. 81 00:05:06,340 --> 00:05:10,190 So let's just head step or. 82 00:05:10,420 --> 00:05:13,260 And you can see that the output is also getting printed here. 83 00:05:13,270 --> 00:05:19,750 The new output in the console let's it step on again and let's step or again. 84 00:05:19,780 --> 00:05:27,420 So we will go back and the control comes here and then it goes with the next declaration. 85 00:05:27,910 --> 00:05:31,120 So let's head control stapler. 86 00:05:31,180 --> 00:05:39,370 This is the second student step over this time not just do a step or so the loop continues again and 87 00:05:39,370 --> 00:05:44,280 it's good booze once again step over step or step over. 88 00:05:44,360 --> 00:05:52,210 Let's do a step into here and one other thing I wanted to show you here as it's printing the name and 89 00:05:52,210 --> 00:05:52,900 gender. 90 00:05:53,140 --> 00:05:58,480 But you can see that it's also blending the student also so if you click on this student as here it's 91 00:05:58,480 --> 00:06:00,520 the local variable of the for loop. 92 00:06:00,700 --> 00:06:08,080 So if you click click here you can see the all the elements of the student object itself. 93 00:06:08,310 --> 00:06:08,630 OK. 94 00:06:08,650 --> 00:06:12,110 So you can see that ID's thousand three name is Anita. 95 00:06:12,250 --> 00:06:15,220 So these are all the variables within the student. 96 00:06:15,220 --> 00:06:21,070 So here variables would show both residue variables as well as object references. 97 00:06:21,070 --> 00:06:24,050 Now let's go here step into. 98 00:06:24,130 --> 00:06:31,930 Now let's look at step written step written words simply execute the methhead and it would take the 99 00:06:31,930 --> 00:06:38,830 control back to the caller and it would move to the next statement after the after the Invoke in location 100 00:06:38,830 --> 00:06:39,340 statement. 101 00:06:39,370 --> 00:06:41,610 OK so let's just head this here now. 102 00:06:41,800 --> 00:06:45,080 So the control came back here and it went to the next iteration. 103 00:06:45,210 --> 00:06:45,750 OK. 104 00:06:45,970 --> 00:06:47,110 So that's separate. 105 00:06:47,410 --> 00:06:55,770 Now let's do one more time step or step or step or up do step or where. 106 00:06:55,810 --> 00:07:02,170 Now here we are at the closing brace at this point it doesn't matter whether we step over or step breakdown 107 00:07:02,230 --> 00:07:03,320 or step in. 108 00:07:03,370 --> 00:07:08,480 So all three would work in the same way sort of just head step over. 109 00:07:08,620 --> 00:07:17,820 And so since we have four students now when I hit a step or so control goes back here to set M.. 110 00:07:18,040 --> 00:07:24,200 So we don't how any other any any other big points we can search more than one break point. 111 00:07:24,580 --> 00:07:30,140 And also one other thing is when we vent here around when we were in print method. 112 00:07:30,400 --> 00:07:36,370 So if we had then we you know when we do step down here it was returning the control back to the calling 113 00:07:36,460 --> 00:07:42,540 motard But if there was any other break point in between then it would stop at the big point. 114 00:07:42,670 --> 00:07:47,090 OK so if there is no magic wand you would call the control would go back with a calling method. 115 00:07:47,170 --> 00:07:47,750 OK. 116 00:07:47,980 --> 00:07:50,960 Now let's go back to the matter let's just had this button. 117 00:07:50,980 --> 00:07:52,690 So back to this matter. 118 00:07:52,750 --> 00:07:57,240 Now if you do step or can just took over. 119 00:07:57,450 --> 00:08:02,160 Now let's see if you're done with your investigation you can either stop here dominate. 120 00:08:02,320 --> 00:08:05,180 You can terminate all you consider is you. 121 00:08:05,290 --> 00:08:08,180 So you can resume the control would raise your hand. 122 00:08:08,190 --> 00:08:12,050 It would stop at the next break point. 123 00:08:13,090 --> 00:08:19,030 OK so let's just head this and we are done with the debugging session. 124 00:08:19,060 --> 00:08:21,180 Now let's look at something interesting. 125 00:08:21,340 --> 00:08:24,060 So let's just go up here. 126 00:08:24,070 --> 00:08:25,280 The student won. 127 00:08:25,720 --> 00:08:27,730 Let's get another break point here. 128 00:08:27,820 --> 00:08:31,010 So here we are creating a student instance. 129 00:08:31,030 --> 00:08:31,380 OK. 130 00:08:31,390 --> 00:08:33,270 And this is the first Torent instance. 131 00:08:33,550 --> 00:08:38,910 So we have two break points in our student test at line 13 on line five. 132 00:08:39,280 --> 00:08:42,510 So let's just go ahead and head and de-bug once again. 133 00:08:42,880 --> 00:08:47,500 So the debugger pauses here and let's So this is. 134 00:08:47,590 --> 00:08:49,200 Here we are creating an instance. 135 00:08:49,210 --> 00:08:51,860 So let's just go into this constructor here. 136 00:08:51,910 --> 00:08:54,330 So let's step in do. 137 00:08:55,600 --> 00:09:01,010 And here you see that it's loading this classic cordless classloader. 138 00:09:01,510 --> 00:09:09,470 And even here here it says that in arts you can see the corresponding stack for him. 139 00:09:09,550 --> 00:09:17,140 Let's get one more step in two and you'll see something else launcher Dark Glass string dark glass. 140 00:09:17,140 --> 00:09:18,980 So what exactly is happening here. 141 00:09:19,300 --> 00:09:25,210 So the thing that is happening is we are in walking we are creating the student instance for the very 142 00:09:25,210 --> 00:09:26,150 first time. 143 00:09:26,350 --> 00:09:31,530 And when that happens GBM first tries to load the Student class into the memory. 144 00:09:31,540 --> 00:09:31,830 OK. 145 00:09:31,840 --> 00:09:36,940 And that process is qualis glassblowing and we will see that in the GBM in dentals chapter. 146 00:09:36,970 --> 00:09:44,740 So every time when we create a new instance every time as it classes access for the very first time 147 00:09:45,040 --> 00:09:46,610 it has to be loaded into the memory. 148 00:09:46,630 --> 00:09:51,090 And that's called class loading and that happens for the very first time. 149 00:09:51,430 --> 00:09:52,850 Not for the second time. 150 00:09:52,900 --> 00:09:59,700 So that's what is happening so when you see this all you can do is just click on separate and separate 151 00:09:59,700 --> 00:10:01,600 and separate and separate. 152 00:10:01,620 --> 00:10:08,370 So now we're back in the main matter and first instance has been created so let's just go to the second 153 00:10:08,370 --> 00:10:09,180 instance. 154 00:10:09,180 --> 00:10:16,720 Now let's head step into now as you can see it's no longer calling the class loading class. 155 00:10:16,800 --> 00:10:25,020 The reason as class student is already in memory and JVM is simply using it to create the need to create 156 00:10:25,020 --> 00:10:26,510 a new instance or an effect. 157 00:10:26,700 --> 00:10:30,240 OK so what we saw happens only the very first time. 158 00:10:30,240 --> 00:10:32,060 So that's the class drawing process. 159 00:10:32,070 --> 00:10:37,680 So the first time it floats into the memory and from the second on time onwards it's just it just uses 160 00:10:37,680 --> 00:10:39,120 the class from the memory. 161 00:10:39,210 --> 00:10:46,190 Ok since it's already loaded into memory now we are here in this construct Let's head step over. 162 00:10:46,380 --> 00:10:52,830 Now you'll see it's not going it's not executing the first statement but for some reason it's getting 163 00:10:52,830 --> 00:10:58,360 here to the this statement where the gender variable and the student is getting initialized. 164 00:10:58,470 --> 00:11:00,340 So what exactly is happening. 165 00:11:00,360 --> 00:11:06,570 The thing is we know that within the constructor the first invocation statement would be a call to call 166 00:11:06,570 --> 00:11:08,580 to the superclass constructor which is. 167 00:11:08,700 --> 00:11:11,790 So we know that there is an super invocation statement. 168 00:11:11,850 --> 00:11:18,870 So basically what happened was the object class got invoked under super invocation statement is an invisible 169 00:11:18,870 --> 00:11:20,380 statement We know that. 170 00:11:20,550 --> 00:11:21,890 And so that got in worked. 171 00:11:21,900 --> 00:11:28,620 So the control window object it created an object instance and then it came back with a subclass which 172 00:11:28,620 --> 00:11:29,530 is the student. 173 00:11:29,700 --> 00:11:34,760 And then it started to initialize all these instance variables so that's what is happening here. 174 00:11:34,800 --> 00:11:40,710 And we will examine it in more detail when we create the next instance so let's just head step over 175 00:11:41,220 --> 00:11:43,380 so step or so we are here now. 176 00:11:43,410 --> 00:11:43,980 Back. 177 00:11:43,980 --> 00:11:50,470 So let's just go back Buist to pretend hits in do OK. 178 00:11:50,490 --> 00:11:52,630 So this is the third student instance. 179 00:11:52,920 --> 00:11:55,230 Now let's do another step in do. 180 00:11:55,530 --> 00:11:56,520 And here we are. 181 00:11:56,550 --> 00:12:01,220 So the object class got invoked. 182 00:12:01,410 --> 00:12:03,180 So that's what has happened. 183 00:12:03,180 --> 00:12:05,280 And we do step over. 184 00:12:05,520 --> 00:12:08,010 So we are back in Student class. 185 00:12:08,390 --> 00:12:12,390 Students take over step over OK so we. 186 00:12:12,420 --> 00:12:13,500 So that's what is happening. 187 00:12:13,500 --> 00:12:17,330 So there is an invisible super in waggish statement as we know. 188 00:12:17,520 --> 00:12:21,360 And here is one more thing I want to point out as. 189 00:12:21,600 --> 00:12:23,620 So here this is a statement. 190 00:12:23,700 --> 00:12:28,150 So if we do step over it would execute this statement and move to the next statement. 191 00:12:28,230 --> 00:12:35,180 But if had this been a method invocation then if we had step into it would go into the matter. 192 00:12:35,190 --> 00:12:36,640 We know what we already know that. 193 00:12:37,020 --> 00:12:41,790 But for this kind of statement which is not a method invocation statement it doesn't matter whether 194 00:12:41,790 --> 00:12:47,210 it is step over or step into or even step into Would we have the same me. 195 00:12:47,250 --> 00:12:51,990 It's just that if the statement involves him at that location then step in and do would really step 196 00:12:51,990 --> 00:12:52,870 into that method. 197 00:12:52,980 --> 00:13:00,150 OK so let's just step into the you see step into step into. 198 00:13:00,150 --> 00:13:01,730 So that's what is happening here. 199 00:13:02,070 --> 00:13:05,100 So there is no difference between step over and step into. 200 00:13:05,120 --> 00:13:07,240 Now another thing I want to point as. 201 00:13:07,240 --> 00:13:12,630 Let's say we came here to this particular statement and you just want to go back and do it go back in 202 00:13:12,630 --> 00:13:18,990 time and you know or Buddha or de-bug once again into the beginning from the beginning of the matter 203 00:13:19,390 --> 00:13:22,200 and that is all you need to do is just click on this. 204 00:13:22,200 --> 00:13:27,210 Drop the frame and it would start again. 205 00:13:27,420 --> 00:13:34,860 But the catch is that the ID variable got initialized 2003. 206 00:13:35,550 --> 00:13:37,190 So the values are not reset. 207 00:13:37,290 --> 00:13:42,780 It's just that the control goes back but the values the instance variable values are not initialized 208 00:13:43,260 --> 00:13:46,640 or even the static variable values will not read or read initialized. 209 00:13:46,800 --> 00:13:47,440 OK. 210 00:13:47,550 --> 00:13:56,630 So let's just go do step over stick or stick or just of course the we're now ID would be 2004. 211 00:13:57,270 --> 00:14:04,130 So that's the drop to frame on your JVM hostile supported in order for you to see these Eikon here. 212 00:14:04,740 --> 00:14:07,240 So let's just do a step taken. 213 00:14:07,410 --> 00:14:09,770 So here we are. 214 00:14:10,300 --> 00:14:14,220 STUDENT 4 let's just take resume here. 215 00:14:14,220 --> 00:14:18,930 So here we are in the for loop just took over. 216 00:14:18,990 --> 00:14:24,640 Now another thing that we can do is here we have the name variable or the generated one. 217 00:14:24,780 --> 00:14:28,190 You can also read said the value so the value is Jo-Anne. 218 00:14:28,200 --> 00:14:33,000 Now let's say for example we want to see what happens if we change it to another. 219 00:14:33,090 --> 00:14:34,670 OK so we can do that. 220 00:14:34,740 --> 00:14:38,080 So you can just right click on Sid change value. 221 00:14:38,280 --> 00:14:41,380 So from Joanne let's say you want to change it to null. 222 00:14:41,490 --> 00:14:42,530 It's just a string. 223 00:14:42,720 --> 00:14:43,180 So hit. 224 00:14:43,200 --> 00:14:43,970 OK. 225 00:14:44,190 --> 00:14:48,750 Now you can see that it is not a novel it's going to print. 226 00:14:48,900 --> 00:14:51,210 Let's let's just step into print. 227 00:14:51,700 --> 00:14:54,480 As you can see the print is not at all. 228 00:14:54,480 --> 00:14:56,010 It's printing now here. 229 00:14:56,340 --> 00:15:03,540 So it's just written soon it's just finished a.. 230 00:15:04,830 --> 00:15:10,270 Now one final thing I want to show is let's just go here. 231 00:15:10,530 --> 00:15:12,400 So let's just say we want to get it. 232 00:15:12,420 --> 00:15:14,900 I mean if we hit resume it's going to finish right. 233 00:15:14,970 --> 00:15:16,430 Because there is no break point. 234 00:15:16,560 --> 00:15:18,360 But let's say we want to stop here. 235 00:15:18,360 --> 00:15:22,830 There is no break point but we still want to stop here at some point in the future. 236 00:15:22,830 --> 00:15:29,640 So what we can do is just put your you know just going near that statement going to that line and just 237 00:15:29,640 --> 00:15:37,830 hit Control are and you can see the control jumps to that particular statement and it exiguous everything 238 00:15:37,830 --> 00:15:38,530 in between. 239 00:15:38,610 --> 00:15:39,170 OK. 240 00:15:39,330 --> 00:15:45,330 So we can do that even though there is no break statement and on what we will do is to control our. 241 00:15:45,780 --> 00:15:47,140 So that's about it. 242 00:15:47,280 --> 00:15:51,060 And let me just run this one more time resume. 243 00:15:51,540 --> 00:15:52,810 So we are done. 244 00:15:52,980 --> 00:15:57,150 Now here are the big points if you want remore all the brick ones at once. 245 00:15:57,150 --> 00:16:01,390 You can click this icon here remore all break points. 246 00:16:01,440 --> 00:16:02,910 So it says are are you sure. 247 00:16:02,910 --> 00:16:04,260 Yes. 248 00:16:04,260 --> 00:16:10,410 Now if you want to remove this you can also do directory more or terminated branches so there is one 249 00:16:10,410 --> 00:16:12,870 more from some other session. 250 00:16:12,870 --> 00:16:18,120 So let's just close this so you can have multiple debug sessions. 251 00:16:18,450 --> 00:16:18,700 OK. 252 00:16:18,710 --> 00:16:20,890 So that's about it. 253 00:16:20,940 --> 00:16:26,610 I think those are all important things that we need to know about about debugging. 254 00:16:26,610 --> 00:16:28,760 And we have blown that. 255 00:16:28,890 --> 00:16:36,140 So what we learned is all the fundamental stuff now in the supplementary notes I will include a pointer 256 00:16:36,160 --> 00:16:42,850 to a really good read you'll see it is that coward's debugging debugger at a very deep level. 257 00:16:42,960 --> 00:16:49,680 Those rules are specific to debugging are not instructed by a person called Mark Baxter and it's really 258 00:16:49,680 --> 00:16:50,410 good stuff. 259 00:16:50,670 --> 00:16:56,690 OK so if you want to go into more details you have to do it you can look at those videos it's over one 260 00:16:56,700 --> 00:16:57,530 hour long. 261 00:16:57,750 --> 00:17:03,690 But what be covered here is definitely the basic stuff fundamental stuff and it should be more than 262 00:17:03,690 --> 00:17:08,760 enough but you can also go and look check all those videos. 263 00:17:09,240 --> 00:17:14,440 Not that debuggers are also used on Glan side to debug issues in Javascript. 264 00:17:14,490 --> 00:17:15,720 So it's not just Java code. 265 00:17:15,720 --> 00:17:18,690 You can also have a debugger or in the client side. 266 00:17:18,690 --> 00:17:22,420 So Wondolowski a debugger I use extensively is cardless firebug. 267 00:17:22,780 --> 00:17:27,690 And it can be installed in the browser and it works pretty much like Eclipse's a debugger. 268 00:17:27,690 --> 00:17:31,320 In fact I think most debuggers would work in a similar way. 269 00:17:31,470 --> 00:17:32,740 So that's about it. 270 00:17:32,740 --> 00:17:34,520 And I hope you enjoyed it.