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Hello everyone.



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So in this video we will discuss some more concepts of object oriented programming.



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So in the last video we discussed about excess modifiers.



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We know how public and private affected the accessibility of the properties of the class.



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So we created this class in the last video.



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It has two properties rule number and age.



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Rule number is public.



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And ages private.



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So let's add one more function to this class and let's make that function public.



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So I have a public function the name of the function is let's say display so what this function will



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do is it will print the age and it will number of the student.



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So a return type will be void C out age space and and but



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so this function displays the H.



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And rule number of the student return type will be void.



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Okay now let's discuss how to call this function.



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So we will call this function using the dot operator just as we use dot operator to access the properties



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we can use dot operator to access or to call the function.



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So for property what we used to do is object name dot property name for calling a function object name



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dot function name.



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Okay.



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So S1 so S1 dot uh what is the name of the function.



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Display s under display.



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Similarly we can call as to dot display and let's call display function for S6 as well.



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Starred as six dot display okay.



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And let's write short also for a six so a six arrow display and that's all okay.



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So this is the V to call a function.



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Now our function is not thinking any argument if our function takes our argument we can positing fantasies



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since our function doesn't take any argument our identities are empty.



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Okay so now what I want to do is uh I want to use this each property outside the class.



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This is properties private.



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So my question is how to access a private property outside the class.



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So the answer is using a function.



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So let's make one more public function uh written by will be in danger and the name of the function



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is.



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Get each.



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So this is a public function but this function will do is it will done each age is a private property.



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So what is happening now here is see this get page function is a public function.



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So since this is a public function we can call it from the other file that is from the student does



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not CPB.



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So we can call this function and this cottage function will return us each whereas age is a private.



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Okay.



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So with the help of this public function we can get the value of private function.



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Now let's see called.



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So this is our file.



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Uh what I want to do is uh see out S1 age



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s dart we will call the function get age get data is a public function.



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So no compulsion that I will be there.



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And similarly let's uh do it for this to as well so see out



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as to age



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as to dart get garbage



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OK let's add an on line here OK.



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Everything seems fine.



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No



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so one more thing uh we can only access the age.



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We cannot set the age.



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So if we will run this program we will get compilation error saying that this age property is private.



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So you cannot access them.



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So let's make uh let's come on get out age and age.



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Okay.



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So now what program will run fine.



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Okay so let's run our program



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Okay so the submitter is found out display what is the arrows.



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Glass rent has no member named display.



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Oh uh.



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We also have to run this file because we did genius to this file.



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So this file should also be run now.



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Uh see out age and lumber.



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Oh it is that is



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CO2 is not declared in this code.



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So the error is uh this see out the functionality of the C out is defined in your stream file so I have



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to include I Ustream here.



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Mm hmm.



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Again it is.



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Okay so this line is defined in namespace.



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So namespace the.



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Now this is fine.



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Uh let's send this file.



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So ages private.



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Okay.



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So we also have to come into it out here and also we have to come into get out



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and is this seems fine.



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Okay so let's print let's get dates for Essex also.



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So see old Essex



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six not get each



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thing everything is fine now.



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Let's start now.



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But now let's run this and now we will run this six year dynamic.



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So for dynamic we have to use data fence celebrated and now let's send this file



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seems like everything is running fine



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okay.



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So let us analyse the output.



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So first of all uh the call the display function.



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So display function will print that each and the usual number.



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So this is the age which is a random value because we have not set it and this is under because we certainly



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number two we entered.



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Okay.



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So after S1 the print is too.



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So if it is true we didn't set any values about the values that got the beach and then we are getting



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that H for this on that each for this one is this it is a random value because it is a private field



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and we have not make of public function to set it.



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Similarly as two ages also a garbage value because we haven't said it.



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And then S1 daughter number which we said to be hundred and after that exit door.



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We said that all number for a six and a six star display.



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So for a six the ages that number Lou and that number is tardy because we said it then again we six.



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Then again uh display function.



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So both are the same.



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And then we got the H for Essex so each for Essex is at random value.



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Okay so the output is expected output is what we expected.



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So instead of like using the lead fence operator and the DART Operator we can directly write Essex had



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a wage



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Yeah.



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It's working fine.



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Okay.



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So so now I can read the property of a private field.



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So if I can read it then they should also be happy to read it.



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So for reading the press or for writing the uh private property what we can do is we can create a function



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void stage so this stage function will take age as input and it will set age to a and that's all.



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Okay so let's come to this class.



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So this class is like we will get confused using this class.



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So I created a new class student new DA CPB.



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So now we will do the work here.



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So for doing something first of all we have to create object.



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So let's create two objects.



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One is starting and that one is dynamic.



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So Student 1.



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Now let's create a dynamic object.



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STUDENT As to new student



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so for this student to work we also have to include the file here so hashing include



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student art CPB.



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Okay so now let's set the age and then we will display so as are not stage oh now let's say a stage



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and let's say the value is 20.



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Similarly for as to as to Edwidge so the S2 0 stage and let's say 30.



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Now let's call as our display



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and as to add or display.



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Okay so now let us run our program



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so as not set age there is something wrong with it glass front has no members her age or I again did



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the same mistake.



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I have to run this file because I did 10 years to this file so this green line means that these men



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alignment of lines I already compiled and this yellow lines means the area to be compiled so called



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Lux's so called logs also help us so now a venue will render program this whole code will become green.



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See now everything is compiled.



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Now it will work.



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It will not draw any other



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so ages 20 and the roll number is garbage value.



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A just 30.



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Rule number is the garbage value



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so in this way we can like we can get the property and we can also set the property.



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Okay.



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A private property.



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So one question that will be coming to her mind is what is the use of making each a private field.



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If we can't read and write it then basically what did we achieved by making it private.



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What is the reason for making something private.



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So look carefully we cannot change the age radically because it's a private field but we have to call



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a function get age or set age to access the private property age.



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Okay so now let's take an example to illustrate to the benefit of private let's say I want to put a



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constraint on age that age cannot be negative.



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If age would have been public then anyone can set it to be minus one.



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How as one dot age equals minus one.



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And it would have been Vogue if the age was public but now the age is private.



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So I can put a constraint here before starting the age.



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What I will do I will check if the input is less than zero then simply done do not do anything.



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Simply written we are not setting age okay so we can add constraint like this.



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So this is the use of private property.



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What we will do we will make a public function to access the private property.



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So now here we can add constraint.



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For example like uh if you want to add more constraint like there should be a password you have to give



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password as well for setting age basically an authorized person can notarized person can only set age.



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So let's say the password is 1 2 3.



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So if password is articles 2 1 2 3 if password is not mandatory then do not do anything simpler then.



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Okay.



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So now we got the property to add the constraint we get the power to add the constraint.



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So I can add multiple constraints here.



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So whenever you are working in a real world project.



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If a property is important that is a third person should not be allowed to use the property.



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So we should make those properties private.



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Okay so this is a good function.



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This is a third function get function.



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We can read and with the help of said function we can write.



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So we generally call it get a function and set the function getter and setter with the help of get the



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function.



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We will get the data with the help of the function we can said that you do okay.



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Thank you.