Lecture 10: Constructors in Java - Default and Parameterized

[Music] [Music] so welcome to the last lecture of classes and objects in the last lecture here we had seen separately how to use default Constructor and parameters Constructors so now so can we use both in a single program right so that we are going to see in this case study or the problem right so let us consider employee management system all right so that is the class so that has employee details such as you have ID name age and salary all right so these are all the member data kind of all right so now the main idea is we have to use both default and parameterized Constructors right so in the same program so when you are going to create the employee objects so we are going to use default and parameterized Constructors so how we are splitting this the default Constructor should contains or initialize the employee with the values ID is zero name unknown age should be 18 and salary is zero okay and then the parameters Constructor should initialize so you should have a employee object let us say another object let us say E2 with certain values by the user so given by the user the specific values given by the user for ID name age and salary also the program should in include the display employee details so we have to display the employee details also we have to do the update in the salary right for example if some employee is getting the salary of 30,000 it should be 40,000 and similarly 3 lakhs it should be 4 lakh something like that that should be update and that update we have to display so the main idea here is how we can use both default and parameterized Constructors so we'll see the program all right so we'll see the C++ program so I have class employee so here I have four member data as suggested in the problem so we have ID whose data type is integer name whose data type is string age integer and salary is double okay so this is your member data and here you have a constraint Constructor right so this is a default Constructor you don't have any parameters so therefore you call this as a default Constructor so in the default Constructor your ID is zero name is unknown age is equal to 18 salary is 0.0 right you have one see out statement the see out statement is printing ID okay default Constructor call the employee with ID so this is an undercode ID will be printed right in fact ID is zero zero should be printed so whenever you are creating an object all right without any parameters so you call this is a default Constructor so it will be automatically invoked and then the sequence of steps will be right executed and you have one C out statement so that means in the console you will get this particular output so now parameter Constructor so here you go the parameters Constructor so you can see both default Constructor and parameters Constructors so they are having same name as class also you can find the usual function we call this as a special member function because you can't find any return type so any member function you can find a return type it may be a wide it may be integer it may be double Etc so whereas in this case you don't have any return type right so that is why it is also called the special member function so now the par petress Constructor you have employee ID string of employee name employee age and employee salary all right so under this you have right so whatever you are passing as a parameter passing as a value in the main all right so that will be initialized to ID name age and salary so again you are displaying the parameters Constructor call for employee with ID so whatever be the ID so that particular ID will be printed so now in the question it was asked we have to do the display details right this is a special member function and here you go you are printing employee ID which is ID right name you have name age you have age all right and salary you have the salary right so this we are printing in the display details that means I want to print all the ID name age and salary of the employees and then your update salary right so I'm passing the update salary as a parameter all right I'm passing as a value all right so it will be the new salary under double all right so the new salary will be assigned to salary that means there is a modification in the salary there is a updation in the salary so in the see out statement you can see salary updated for employee with ID right so you have ID and salary will be displayed and you can look here the class is ending over here okay so we have completed the class so now when we go to the main program so you have created the first object emp1 under employee class you have emp1 right so whenever you are creating this object we know that right so whenever you are creating this object so your uh default Constructor will be automatically called right employee want the default Constructor so in the default Constructor so what is there so we had seen so the default Constructor you have ID zero all right name is unknown age is 18 salary is 0.0 so initialize and then it is see out statement and then you have one see out statement so there you have default Constructor call for employee with ID all right so the ID will be printed what is the id id is zero so you will get the output default Constructor call for employee with id id right so that will be printed right so this is what the next line line number 51 you have emp1 do display details so the display details here you go all will be printed right the ID zero name is unknown a age is 18 and salary is 0.0 so this will be printed so we have done up to line number 51 and line number 54 right emp1 is invoking update salary right and then you are passing 30,000 all right so when you are updating this salary so now new salary will be assigned to salary so now that means when you are calling emp1 that means emp1 is invoking display details that is a change all right so there is a change so what is the change you can have right so this is the one zero unknown 18 0.0 and then since you have this update all right so you will have salary updated for employee with id0 to 30,000 right so that will be printed for employee one all right I hope it is clear and then see out endl that means it it will go to the next line so now you are creating a second object right and then you will have the parameterz right you are passing the parameters so therefore the parameters Constructor will be invoked all right so parameters Constructor when invoked you're pausing 99 ashmin 38 and 400,000 all right so that means when you go here your employ ID so ID will be 99 name will be Ashwin age 38 and salary will be 400,000 so the id id is 99 will be printed over here right so when emp2 is invoking display details all these information will be printed in line number 60 and uh there is a salary update all right that 4 lakhs will be now 5 lakhs 400,000 will be now 500,000 so in that case when emp2 is invoking update salary 500,000 so you can see that all right so here the new salary is 500,000 so that will become the salary in line number 42 that will be assigned to salary so salary updated for employee with id99 to 500,000 will be printed right so this is what exactly happening and then you have return zero then you can see the list of output all right so initially your employee ID is zero right so whenever you are creating an object right whenever you are creating an object so in the default Constructor so you have this display message all right in the default Constructor all right so in the default Constructor you have this message what is the message the default Constructor called for employee with ID zero right so that will be printed so it is what you are getting as a first output and then employee details employee ID is zero name is unknown age is 18 and salary is zero and similarly employee ID right for there is a salary update yes there is a salary update so the salary update function when you are calling right when employee one is invoking so you are getting this output salary updated for employee with ID 0 to 30,000 right employee ID zero so now he or she is going to get 30,000 that is the meaning and uh rest of them are similar ID name age and if you look salary now it is becoming 30,000 so this is the default Constructor and in the parameterized Constructor all right so whenever it is calling when you're creating an object emp2 all right under the employee ID 99 all right so employee ID is 99 name is Ashwin age is 38 and salary is 400,000 right so initially and there is a salary update salary update has gone from 400,000 to 500,000 so when emp2 is invoking right the details all right employee details or updated details so salary is updating from 400,000 to 500,000 so that will be displayed for id99 to 500,000 and rest ID name age is same and salary there is a change now the display is 500,000 all right I hope you have understood this particular program so here we can see right in this problem so they are asking us to use both Constructors default Constructor as well as the parameter Constructor and I hope it is very clear now so similarly in Java we will see the concept of default Constructor right so let us consider in this case there are two classes right in this case there is a class bike one all right and then you have in fact this is a driver class right so you have void main so therefore you call this as a driver class so you have only one class and in this class itself you have a void main so you call this as a driver class in Java all right so the class B one and this carries same name so we know that from C++ so we know that this is a Constructor and no parameter therefore you call it as a default Constructor so here system.out.print it is equalent to C out bike is created right so this is what it's going to display in the case of construct when you are creating an object so now here you are creating an object so slightly different from our usual C++ so it's a everything is dynamic in Java so here you have an object small B under the class B one and dynamically you are creating a memory for bike one so new is the operator for dynamically allocating a memory the new operator and bike one right it's a Constructor correct so B so this B will have will be in some address right is object object B will be in some address so now we are printing out system.out.print and B right so let us see what is the output we are going to get first when you're creating an object bike is created will be printed and the second one right so we'll see this is the output we are going to get so the second output so we have run in uh uh shell all right the Linux so Java C is for compilation bye one. Java is the name of the file and the second one is running the program Java Blank Space bike one all right so you can see the output bike is created will be printed so that means whenever you are creating an object default Constructor will be invoked and bike is created will be printed all right and next one you call this as the identity Ash map all right you call address in C++ right you call this as address in C++ in Java you call this as identity Ash map so when you're trying to print B the object in fact the location is equivalent to this all right the location the location in Java you call it as identity Ash map all right so that identity Ash map will be printed so the address location other words it's called address location so now what will happen if I create exactly like your C++ bike B all right bike B I have not put any right print statement so when you are creating an object so what is happening so we'll see right I try to compile and run the code all right so you can see unlike in C++ first of all it is not calling the default construct program is running right I can able to compile and run the code all right so whereas if you look I am not getting any output correct so the object is being created but it is not invoking the default Constructor so line number eight so that is the reason so it should be the dynamic in nature so if you look at line number eight so this is the right way to do in Java so bike one B that means B is the object B one is a class that is equal to the new operator and byon exactly like the dynamic array that you do it right it's a dynamic object all right so we have done right or you might have done int star a I put star in in C++ equal to new in of 10 Dynamic array of length 10 all right this is in C++ the same code in Java in you have the array notation a equal to new in of 10 so when you create an array you use this so similarly here new right new and then bike one right the same inte a data type so here we are writing int with the size so here you are writing bike one it's like a Constructor exactly you're putting the Constructor syntax or notation all right but the problem is when you're not dynamically allocated the memory so even the default Constructor will not be called so now we will see right the program will run all right there is it's not giving any error so I can I can able to compile Java C stands for compile bye one. Java is a name of the file and for executing or running the code we use Java by one without extension so you can try in Linux or you might have already done in the case of the basic programming right procedural oriented programming so now what I will do I'll just remove the common statement right so here line number nine I made a common statement I able to right run the code but with common statement what is happening right so without common statement what is happening so now if I try to run this code so I will get an error right so B is not being initialized right the error message that I am getting B is not initialized right so that means you are not able to dynamically create a memory for B so where it is being stored the compiler does not know right so when I try to compile itself you are getting the compilation error all right where it is being stored and then you trying to write the storage location right you're trying to write the identity Ash map or you're going to find out the identity Ash map right so therefore if you look I am getting an error right so line number eight what we have correctly did so this is required right so dynamically we have to allocate the memory so maybe we'll look at one program with the combination of both default and parameter Constructor in Java all right so let us consider class perimeter right so let us consider class perimeter so there you are having two member data one is length and another one is breadth right so here you have the default Constructor so under this default Constructor your length is zero and breadth is zero right your length is zero and breadth is zero in the default Constructor you are initializing length equal to zero and breadth is equal to zero all right so now we will see the parameters Constructor parameter Constructor you have two parameters right so I have two arguments one is int X and int y so x i Am assigning to length and Y I am assigning to breadth all right so now I have one method so the member function in C++ in Java you call it as a method so calore perimeter we are calculating the perimeter so the perimeter is nothing but 2 into length plus breadth right the perimeter is nothing but 2 into length plus bread Okay so so it is printing so whatever you are calculating will be assigning to Perry and system.out.print L the perimeter of the rectangle is right so you are printing the perimeter and line number 25 your class is getting over right your class is getting ended over here so now if I go to the main all right so class const example is a driver class right so you have two classes here so one class is perimeter right since you don't have a main over here this is not a driver class and here you go so const example is the driver class so in the driver class you have a main program right so I have two objects here right one is perimeter P1 P1 is an object we are using the new operator and perimeter means it's a default Constructor so now you are understanding right so the bike we have done the same thing bike one b equal to new by one right it's a default Constructor it is calling and here line number 32 you can see perimeter P2 P2 is an object so that is equal to new perimeter of 25 comma 100 you are passing 25 comma 100 so when I creating P1 one right what is happening so when I creating P1 so when I'm creating P1 the default Constructor will be called your length is zero and breadth is zero that's it right your length is zero and breadth is zero I hope you understand length is zero and breath is zero and when you are creating an object P2 you are pausing 25 and 100 all right when you are calling P2 to you are pausing 25 and 100 so what is happening we'll see when you're pausing 25 and 100 so this is your parameterized Constructor X will take the value 25 and Y will take the value 100 so now that will be assigned to length and breadth for object P2 right so this is what exactly happening all right so now we'll see what are the what are the further methods it is calling so now P1 is invoking the method calore perimeter right so P1 is invoking calore perimeter so when P1 is invoking this so here you go all right so you have a local variable Perry we know for the P1 length is zero and breadth is zero right so this is what happening in the default Constructor so the default Constructor when I go back so you can see over here your length is zero and breadth is zero correct so now when it is calculating 2 into 0 so the result should be zero in the case of first object right your X is zero and Y is zero right so the perimeter should be zero and in the second case you're passing 25 and 100 right when it is calling calculating the perimeter function right calcal underscore perimeter Method All right what is happening you're passing x25 all right length becomes 25 all right so length becomes 25 and breadth becomes 100 so we know that 100 + 25 125 125 into 2 so I have to get the output 250 for second case right I have to get 250 for the second case so first output is zero second output should be 250 so this is what the output we have to get so when I run the code all right so Java C so const example. Java is the name of the program right name of the file const example. Java so Java C is a compilation and next one next line we are running the code execution so Java const example without extension so here you can see the output the first output is the perimeter of the rectangle is zero all right even you can modify the perimeter of the first rectangle or the first object right so whatever you're writing this is going to be printed right so the perimeter of the rectangle in fact yeah so here you can modify so here right line number 23 so we can modify accordingly but the case is you have the member function or method so you have written the perimeter of the rectangle so that is what it is printing maybe what we can do in the Constructor itself we will write see out some statement right so we are trying to find out the perimeter of the rectangle correct something like that otherwise in both the cases we are getting the same output so you may ask the question right so this we can control in the Constructor you make one see out statement I mean to say system. out. print LM statement so the perimeter of the rectangle is zero and the perimeter of the rectangle you are getting 250 right so in this chapter we had seen extensively all right you have in fact initially I started with objects and classes all right so you know how to define a class and how to create the objects and now you can also know how to create the dynamic objects with the help of right in Java right so you know the difference between the static object and dynamic object so in particular right you can use a static object in C++ which is not a problem we still call the default Constructor whereas we are finding some problem in Java when you are creating only the static object the program is running but when you're trying to find out what is a location or identity Ash map it is giving a error so in the case of java so what we have to do we have to create the dynamic objects so once you are creating the dynamic object the syntax should be like a line number 31 and 32 right so you are creating two objects P1 and P2 so P1 you can see the right hand side new that is the operator and then you have the Constructor so that Constructor is nothing but the default Constructor all right so this is nothing but the default Constructor and the second case it is a parameterized Constructor so P2 your classes perimeter with the help of new operator so you have default Constructor so you can try the similar code in C++ also all right so the dynamic nature it will work because in the case of array I gave an example in Star a equal to new int of 10 right you're using the star operator all right the D reference operator correct so in a similar way when you have the Constructor like a default Constructor and parameterized Constructor when there is no arguments you call this as a default Constructor so this is a default Constructor and if you're passing certain parameters right if it is having or you're passing certain values or in the Constructor if it is having some arguments you call this as a parameterized Constructor so you know whenever you are creating an object so which one should be called and as I also said the constructors are nothing but the special member function or the special method it looks exactly like a method or it is is looking exactly like a function but it does not have any return type all right so this is what even in Java also we had seen all right so line number 13 if you look it does not have any return type and they have the same name as of class so therefore it is called the constructors so in both the programs we had seen usage of default and parameters Constructors in the same program right so we had seen different example the default parameterized separately and in C++ we had solved one case study the combination of default and parameters and similarly in the case of java we had seen the default Constructor and also one example of using both default and paramet Constructor so in this chapter we extensively studied this class objects and the constructors so with this I'm concluding thank you [Music]