1 00:00:01,450 --> 00:00:02,200 Hello everyone. 2 00:00:02,200 --> 00:00:07,890 So today we will learn about constructors before starting today's video. 3 00:00:07,900 --> 00:00:15,690 I want to cover two more things that I forgot to cover in the last review so the first thing is see 4 00:00:16,590 --> 00:00:20,260 we have public private and then again public. 5 00:00:20,250 --> 00:00:27,630 So this whole gold belongs to public discord belongs to a public so we can write we can write this code 6 00:00:27,630 --> 00:00:29,610 in a better way in a better manner. 7 00:00:29,670 --> 00:00:32,300 So how to optimize this code. 8 00:00:32,370 --> 00:00:41,350 First of all let's remove and document from here and put it in the public section and let's remove this 9 00:00:41,350 --> 00:00:46,040 line. 10 00:00:46,080 --> 00:00:49,630 So now we write public only one time. 11 00:00:49,650 --> 00:00:53,370 And similarly there is no need to write private way. 12 00:00:53,470 --> 00:00:54,510 Let me show you. 13 00:00:54,630 --> 00:00:57,590 See this age is private. 14 00:00:57,600 --> 00:00:58,860 Why. 15 00:00:58,950 --> 00:01:05,280 Because there is no access modifier defined above it so by default the access modifier is private. 16 00:01:05,340 --> 00:01:06,930 So there is no need to write private. 17 00:01:07,380 --> 00:01:11,150 And similarly in the previous code public was written two times. 18 00:01:11,190 --> 00:01:15,040 But here public is right here we write public only one time. 19 00:01:15,080 --> 00:01:15,320 Okay. 20 00:01:15,330 --> 00:01:16,590 So this code is much better. 21 00:01:16,590 --> 00:01:20,610 Earlier it was like public public and then private. 22 00:01:20,610 --> 00:01:22,110 And then again public. 23 00:01:22,170 --> 00:01:24,500 So this doesn't seem right to me. 24 00:01:24,540 --> 00:01:25,620 This one is much better. 25 00:01:25,620 --> 00:01:31,170 We are using we are using the properties what property first we are using their default property that 26 00:01:31,170 --> 00:01:32,070 default is private. 27 00:01:32,070 --> 00:01:36,110 So there is no need to write private and we are writing public on live ones. 28 00:01:36,530 --> 00:01:37,130 Okay. 29 00:01:37,140 --> 00:01:43,470 Second thing that I want to cover is how display function can access each and all no fee. 30 00:01:43,470 --> 00:01:45,000 Rule number is public. 31 00:01:45,090 --> 00:01:50,730 So rule number can be accessed anywhere in the program but ages private since age is private. 32 00:01:50,730 --> 00:01:55,540 It can only be accessed within this class and display function is defined within this class. 33 00:01:55,620 --> 00:02:01,440 So display function can access each similarly gated function can also access each because good its function 34 00:02:01,440 --> 00:02:04,070 is also defined in the student class. 35 00:02:04,140 --> 00:02:11,040 And similarly stage function can also access private variable each because this function is also defined 36 00:02:11,100 --> 00:02:12,410 within the class. 37 00:02:12,420 --> 00:02:16,940 So these are the two things that I want to look about in the last radio but I forward to color. 38 00:02:16,950 --> 00:02:17,340 Okay. 39 00:02:17,340 --> 00:02:19,910 Now let's start with I this topic. 40 00:02:20,090 --> 00:02:26,280 So till now we have learned how to create classes how to create objects of a class and how to access 41 00:02:26,280 --> 00:02:29,530 properties of the object and access modifiers. 42 00:02:29,580 --> 00:02:33,420 Let's see what our construct does and how to use them. 43 00:02:33,480 --> 00:02:39,200 So when we write student S-1 what will happen 44 00:02:42,840 --> 00:02:48,100 rule number age and we get a garbage values in these fields. 45 00:02:48,120 --> 00:02:48,660 Okay. 46 00:02:48,690 --> 00:02:51,810 So if I will do s not display 47 00:02:54,570 --> 00:02:56,210 these two will get printed. 48 00:02:56,490 --> 00:02:57,260 Fine. 49 00:02:57,300 --> 00:02:59,720 Now let's analyze this a statement. 50 00:03:00,870 --> 00:03:03,360 Let's analyze this run properly what will happen. 51 00:03:03,420 --> 00:03:08,190 So this internally in debates in this we as one art student 52 00:03:11,670 --> 00:03:17,970 internally this statement will be executed in this fashion as one art student. 53 00:03:18,480 --> 00:03:21,200 So what is the meaning of astronaut student. 54 00:03:21,270 --> 00:03:31,880 So we can see here student is a function just like display student is a function just like the display 55 00:03:32,090 --> 00:03:39,310 and S1 object is calling that function but this function name is same as last name. 56 00:03:39,650 --> 00:03:44,440 The name of other classes is student and the name of the function is also student. 57 00:03:44,480 --> 00:03:47,200 So the function name is same as last name. 58 00:03:47,210 --> 00:03:54,290 So this function is called constructor this function is called constructor. 59 00:03:54,460 --> 00:03:56,730 So what is the purpose of a constructor. 60 00:03:56,980 --> 00:03:59,450 So it will do one simple thing. 61 00:03:59,530 --> 00:04:04,580 It will initialize the data member or the properties with the garbage values. 62 00:04:04,600 --> 00:04:14,100 Okay so properties and the name of properties are data members data member okay. 63 00:04:14,270 --> 00:04:20,390 So what this constructively Lou it will initialize the data member or we can say the properties of the 64 00:04:20,390 --> 00:04:22,500 object with the garbage values. 65 00:04:22,580 --> 00:04:29,090 So that's why these two properties are initialized with the God which values because this is the work 66 00:04:29,090 --> 00:04:36,750 of dysfunction so constructor function has some special properties. 67 00:04:36,750 --> 00:04:39,860 So construct basis special function. 68 00:04:39,900 --> 00:04:49,590 Now let us write some of its properties first its name will be seen misc last name so same name as the 69 00:04:49,590 --> 00:04:52,820 name of the class second. 70 00:04:52,940 --> 00:04:55,220 This function has no return type 71 00:04:58,700 --> 00:05:02,350 third properties no input argument 72 00:05:07,370 --> 00:05:08,390 no input argument. 73 00:05:08,810 --> 00:05:15,940 So these are the properties of a constructor or we can say default constructor. 74 00:05:16,060 --> 00:05:21,410 These are some of the properties of the default constructor. 75 00:05:21,630 --> 00:05:33,020 Okay so let's analyze it a bit more so I am saying when we write student S1 this statement internally 76 00:05:33,030 --> 00:05:40,980 will be interpreted as S1 dart Student object name dart function name. 77 00:05:40,980 --> 00:05:45,120 So now the question is how we created this function. 78 00:05:45,160 --> 00:05:51,720 No we have not created this a student function in our class but this function is being called and other 79 00:05:51,720 --> 00:05:54,350 properties are initialized with their default values. 80 00:05:54,360 --> 00:05:56,280 That is the god of basic values. 81 00:05:56,460 --> 00:05:57,810 So what happened is. 82 00:05:57,840 --> 00:06:02,610 So as soon as we create a class constructor is automatically created. 83 00:06:02,670 --> 00:06:08,370 So we do not need to create it so we can use this inbuilt constructor to initialize the properties of 84 00:06:08,370 --> 00:06:09,660 our object. 85 00:06:09,690 --> 00:06:16,710 Okay so we get a default constructor as soon as we create a class we can also create constructor on 86 00:06:16,710 --> 00:06:17,630 our own. 87 00:06:17,730 --> 00:06:20,520 We will see in some time how to create our own constructor. 88 00:06:21,270 --> 00:06:25,200 Okay so now let's see how the inbuilt constructor look like. 89 00:06:25,620 --> 00:06:33,390 So I told you there are some properties first there will be no return type so empty and then the name 90 00:06:33,390 --> 00:06:36,930 of the function will be say now name of the constructor will be same ethic last name. 91 00:06:36,930 --> 00:06:38,550 So the class name is student. 92 00:06:39,180 --> 00:06:43,030 So the name of the function is student no input argument. 93 00:06:43,170 --> 00:06:50,940 And similarly it will larger than anything no return type no argument and same name as the class name. 94 00:06:51,090 --> 00:06:53,280 In fact we can remove the remote. 95 00:06:53,310 --> 00:06:53,980 Okay. 96 00:06:54,000 --> 00:06:56,220 And also this. 97 00:06:56,220 --> 00:06:56,620 Okay. 98 00:06:56,730 --> 00:07:02,740 So this is the default constructor default constructor will look like this. 99 00:07:06,380 --> 00:07:09,050 So what are the properties of default constructor. 100 00:07:09,050 --> 00:07:11,150 Same name as the class name. 101 00:07:11,150 --> 00:07:13,700 No input argument and no return type. 102 00:07:15,320 --> 00:07:21,710 So as soon as we create an object this function or we can say this construct they will be called for 103 00:07:21,710 --> 00:07:24,390 every object we create constructively record. 104 00:07:24,470 --> 00:07:26,900 So what is the purpose of a constructor. 105 00:07:26,900 --> 00:07:34,850 So the purpose of a constructor the work of a constructor is it initialized the object initialize the 106 00:07:34,850 --> 00:07:41,110 object or we can see it initialize is the property of an object but the default values with regard to 107 00:07:41,110 --> 00:07:43,400 basic values okay. 108 00:07:43,510 --> 00:07:49,660 So for every object constructor will be called only once in the lifetime of the object so then it will 109 00:07:49,660 --> 00:07:53,880 be called it will recall at the time of creation of the object. 110 00:07:54,090 --> 00:08:06,000 Okay let's see some example then you will understand it better if I write student S1 then this function 111 00:08:06,000 --> 00:08:09,320 will be called if I will right. 112 00:08:09,390 --> 00:08:16,290 Student S2 then this function will be called even if I create dynamic object. 113 00:08:16,290 --> 00:08:19,140 Student Start S3 is new student 114 00:08:22,940 --> 00:08:24,880 then this function will be called. 115 00:08:24,920 --> 00:08:32,720 So basically the constructor will be called only once in the lifetime of the object at the time of the 116 00:08:32,720 --> 00:08:33,830 creation of the object. 117 00:08:35,050 --> 00:08:38,620 Okay and how all this statement will be interpreted internally. 118 00:08:38,620 --> 00:08:42,750 So this is same as S1 not student 119 00:08:45,730 --> 00:08:49,910 and this is S2 dart student. 120 00:08:50,140 --> 00:08:56,590 So internally these statements will be interpreted like this and how will the statement will be interpreted 121 00:08:56,590 --> 00:08:57,540 internally. 122 00:08:57,620 --> 00:09:00,500 Star S3 dart. 123 00:09:00,730 --> 00:09:01,840 Function name. 124 00:09:01,900 --> 00:09:06,590 Student or we can see S3 ATL student 125 00:09:11,150 --> 00:09:13,370 Okay so now let's seeing called 126 00:09:17,250 --> 00:09:18,420 Let's Make a constructor 127 00:09:21,000 --> 00:09:22,650 let's make a default constructor 128 00:09:28,170 --> 00:09:32,000 so the function name will be same as the class name last name is student. 129 00:09:32,010 --> 00:09:34,240 So function name will also be student. 130 00:09:34,440 --> 00:09:37,660 There will be no input argument. 131 00:09:39,040 --> 00:09:40,200 And that's all. 132 00:09:40,240 --> 00:09:42,100 So this is our default constructor. 133 00:09:43,030 --> 00:09:48,780 Okay now internal constructor will look exactly like this. 134 00:09:48,790 --> 00:09:57,820 Now one important thing is as soon as we create our own constructor the internal constructor is no longer 135 00:09:57,820 --> 00:09:59,200 available to us. 136 00:09:59,290 --> 00:10:01,990 So this is the constructor that we have created 137 00:10:05,070 --> 00:10:10,500 so as soon as we create our own constructor and then construct that is no longer available to us. 138 00:10:10,500 --> 00:10:16,180 So now if we really create object then I will constructively be called internal constructor will not 139 00:10:16,220 --> 00:10:18,870 recall because it is not there. 140 00:10:18,870 --> 00:10:23,740 Okay so I would constructively do the same book as the internal construct I was doing. 141 00:10:23,940 --> 00:10:30,070 That is it will initialize every property of the object to a default value okay. 142 00:10:30,120 --> 00:10:31,370 Now let's see 143 00:10:35,250 --> 00:10:38,630 let's say some statements here a brand statement. 144 00:10:38,730 --> 00:10:39,480 So we'll see out 145 00:10:44,630 --> 00:10:45,470 Gestapo guard 146 00:10:51,410 --> 00:10:51,710 okay. 147 00:10:51,720 --> 00:10:54,780 Now let us create some object here. 148 00:10:55,150 --> 00:11:07,520 So student S1 student S1 what will happen as soon as this object is created it will call the constructor 149 00:11:07,520 --> 00:11:13,270 that we have created and Daniel construct does not do really well because we gave it our own constructed. 150 00:11:13,530 --> 00:11:18,940 Now let's call the function display word display function will do it will print that you gender number 151 00:11:19,010 --> 00:11:22,020 and since the agent that all number we have not set out oneself. 152 00:11:22,070 --> 00:11:31,340 They both contain God which values similarly let's create another object student S2 and let's call the 153 00:11:31,340 --> 00:11:36,000 display function. 154 00:11:36,280 --> 00:11:43,180 Now let's create a dynamic object so slowly start history as new student 155 00:11:51,170 --> 00:11:55,920 and let's call the display function. 156 00:11:56,030 --> 00:11:57,770 OK so what will we do. 157 00:11:58,100 --> 00:12:03,130 So if I had run this file what will be out I would put first. 158 00:12:03,170 --> 00:12:04,670 I created this object. 159 00:12:04,700 --> 00:12:07,380 So what will happen constructively recalled. 160 00:12:07,460 --> 00:12:16,370 So output will be constructor called and then display function will print the agent that will number 161 00:12:16,460 --> 00:12:17,390 both out of garbage. 162 00:12:17,420 --> 00:12:23,180 So garbage value garbage value then then the concept will be called for object as to so output will 163 00:12:23,180 --> 00:12:24,410 be constructor called 164 00:12:27,680 --> 00:12:32,050 and then it will print the garbage will lose each and the roll number both out of garbage. 165 00:12:32,060 --> 00:12:37,940 And similarly for this concept called and garbage value of each garbage value overall number. 166 00:12:37,940 --> 00:12:39,860 So this is I would expect it output. 167 00:12:39,860 --> 00:12:42,470 Now let's see where do we add output. 168 00:12:42,470 --> 00:12:45,240 So first we have to run this file. 169 00:12:45,410 --> 00:12:49,240 Now we will run this file. 170 00:12:49,290 --> 00:12:52,850 Now you can see the output concept called for object S1. 171 00:12:53,040 --> 00:12:58,380 Then the garbage values of a general lumber concept called for object as to garbage value of a general 172 00:12:58,380 --> 00:13:04,410 lumber concept called for Dynamic object as tree and the garbage values of a general number. 173 00:13:05,190 --> 00:13:05,810 Okay. 174 00:13:05,820 --> 00:13:09,250 So whenever we create objects and build constructive will be called. 175 00:13:09,540 --> 00:13:15,810 But if we create our own concept then our constructed will be called and internal constructor will vanish 176 00:13:16,010 --> 00:13:18,220 and mental construct that will go away as soon as. 177 00:13:18,240 --> 00:13:27,130 Because as soon as we create our own constructor Okay so we can create many constructors for example. 178 00:13:27,170 --> 00:13:33,180 This is our default sector let's create a bad image based constructor. 179 00:13:33,180 --> 00:13:36,000 So betterment based constructor. 180 00:13:36,100 --> 00:13:41,630 So as the name suggests this construct that we have big arguments. 181 00:13:42,220 --> 00:13:46,000 This constructor will take barometers as input. 182 00:13:46,060 --> 00:13:51,010 So function name will be seen as the class name which is the student. 183 00:13:51,340 --> 00:13:53,110 And let's say take input. 184 00:13:53,110 --> 00:14:00,600 Rule number and what it does is it will be assigned all number with a better metered 185 00:14:03,170 --> 00:14:06,130 and let's say 8 brand statement. 186 00:14:06,350 --> 00:14:08,420 So see out constructor to 187 00:14:13,240 --> 00:14:14,470 constructor to guard 188 00:14:23,270 --> 00:14:23,780 so 189 00:14:29,210 --> 00:14:30,610 so if you will create. 190 00:14:31,160 --> 00:14:36,550 So if we will create object with no parameters then this function will be called this constructively 191 00:14:36,560 --> 00:14:37,020 recall. 192 00:14:37,370 --> 00:14:43,390 And if we will create our object with one barometer then this function will be called. 193 00:14:43,550 --> 00:14:46,510 Okay let's take an example to understand it better. 194 00:14:50,760 --> 00:14:58,110 So if I will write student s for what will happen the default constructor will be called because there 195 00:14:58,110 --> 00:15:06,390 are no barometers but if I write if I pass a bad amateur student s Food a barometer then now what will 196 00:15:06,390 --> 00:15:08,670 happen bad image tries to construct it will be called 197 00:15:12,130 --> 00:15:20,530 See when I write student s for it will be interpreted as S for dot student 198 00:15:24,090 --> 00:15:29,880 and this student is the default constructor that we have defined a default constructor. 199 00:15:30,100 --> 00:15:36,480 But I want to call betterment based constructor so for betterment based constructor I have to pass one 200 00:15:36,480 --> 00:15:42,090 barometer which is when we have 2 percent in digital barometer. 201 00:15:42,120 --> 00:15:49,340 So this land will be interpreted as as for dot student and Ben. 202 00:15:49,510 --> 00:15:49,960 Okay. 203 00:15:50,040 --> 00:15:55,370 Now this time betterment tries to construct a will be called okay. 204 00:15:55,560 --> 00:16:00,370 So this is the concept of functional learning. 205 00:16:00,510 --> 00:16:05,610 We have covered function overloading earlier this is seem this is same as the concept of functional 206 00:16:05,610 --> 00:16:05,940 learning. 207 00:16:05,940 --> 00:16:11,820 We have two functions but one function doesn't take any input any barometer as input. 208 00:16:11,820 --> 00:16:14,790 And the second function take one digit argument as input. 209 00:16:14,790 --> 00:16:15,950 So these two are different 210 00:16:23,100 --> 00:16:24,750 so as for our display 211 00:16:32,830 --> 00:16:36,190 now lives in our program OK. 212 00:16:36,220 --> 00:16:40,780 So we have to run this file first and now we will run this file 213 00:16:45,490 --> 00:16:48,100 see constructor to call for object. 214 00:16:48,100 --> 00:16:54,160 As for constructor to is being adding Guard and as photo display print age and that remember so rule 215 00:16:54,160 --> 00:16:56,860 number is Ben because we set it and ages. 216 00:16:56,860 --> 00:16:58,630 I've got a visual view okay. 217 00:17:00,510 --> 00:17:02,550 Let's see you again see out 218 00:17:07,250 --> 00:17:18,170 betterment days to construct our demo. 219 00:17:18,240 --> 00:17:19,530 Now let's run this fighting 220 00:17:22,620 --> 00:17:29,460 see Batman based constructor demo constructor to call because it passed one input one integer argument 221 00:17:29,460 --> 00:17:36,720 as input and rule number is ages a garbage value at all but it's ten by ten because we set rule number 222 00:17:36,790 --> 00:17:37,620 with. 223 00:17:37,990 --> 00:17:38,250 Okay 224 00:17:41,600 --> 00:17:53,970 similarly we can create dynamic objects as well so student star S5 is new student and we have to pass 225 00:17:53,970 --> 00:18:00,370 an integer argument so 20 as faith not display 226 00:18:06,110 --> 00:18:08,560 okay sorry I say federal display 227 00:18:15,110 --> 00:18:22,360 so constructor to call the value of age as a garbage value and the value for number is 20 228 00:18:25,180 --> 00:18:25,650 so 229 00:18:29,610 --> 00:18:39,680 so for one object only one constructively regarded it will never happen that default and betterment 230 00:18:39,760 --> 00:18:45,230 based construct both are being getting called no if there is one object only one construct a little 231 00:18:45,230 --> 00:18:50,810 bit called only at the time of the creation of the object constructively recalled only at the time of 232 00:18:50,810 --> 00:18:52,610 the creation of the object. 233 00:18:52,640 --> 00:18:58,850 Okay so this is very important for every object when constructed will be called only at the time of 234 00:18:58,850 --> 00:19:01,010 the creation of the object. 235 00:19:01,010 --> 00:19:04,560 Okay so we will learn more about constructor in the next video. 236 00:19:05,120 --> 00:19:05,540 Thank you.