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We've already established in part one that there's going to be some inheritance involved, more specifically

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if you go back to your requirements.

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You can see that checking savings and loan share common fields and name in balance.

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And it doesn't make any sense to keep defining the same fields over and over.

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That's when you're going to find yourself copying and pasting code.

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And you know my thoughts on that, never do it.

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Instead, every account is going to inherit fields from a parent class, so I'm going to put an account

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in Java file inside of the account folder.

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All right, in the count class is going to serve as the parent for checking savings and loan.

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Once again, going back to the requirements.

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The developer is only permitted to create an object of type checking savings and loan.

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They are not permitted to create an object of the account class.

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So what we can do is make this abstract.

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And what it's going to do is basically forbid the developer from creating an object of the account class.

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The only purpose of account is to provide inheritance for its children.

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And we also know every account needs to inherit a string ID.

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Now make sure it's private.

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Private string name.

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And a private double balance.

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All right, now, we can create a constructor for the parent class.

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Public accounts.

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Actually, you know what?

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We can just use the Java code generator extension.

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We will generate a constructor using all fields, and we can do the same thing for the copy constructor,

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but instead of getting values from a bunch of parameters, we're going to get the values from a source

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object, the object that we're copying values from sorry start IDs or start name, sorry start balance.

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Now we could do the getters and setters again, just generate them using the extension.

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Pretty easy.

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All right.

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And now that we've set up the parent class, every child is going to inherit the fields and methods

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that we defined in our parents.

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And so checking is going to inherit the fields and methods from the account class.

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So it's going to extend account.

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Savings is also going to inherit fields and methods from the account class.

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And so will the alone account class extends accounts.

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And now we're getting errors because every child needs to have a constructor that synchronizes with

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the parents constructor.

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So we're going to create a constructor instead of checking public checking.

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The constructor is going to receive three parameters a string ID.

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String name and double balance.

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And we're going to use these parameters to update the fields that our checking object is going to inherit.

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So our constructor needs to borrow the super constructor.

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Basically, this line of code is calling the constructor inside of the parent class, and that constructor

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is going to update every field inside of the current object.

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All right now, create a copy, constructor.

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I'll make some space here.

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Public checking.

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That's going to receive a source object checking.

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Source.

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And once again at this constructor needs to borrow the copy constructor inside of its parent.

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This line of code is calling the carpet constructor inside of the parent class.

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And it's this constructor that's going to update every field inside of the current object.

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OK, now we basically do the exact same thing inside a savings critic instructor, public savings.

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And the constructor is going to receive three parameters.

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String ID.

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String name.

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And double balance.

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And we're going to use these parameters to update the fields that are receiving the object is going

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to inherit.

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So our constructor needs to borrow the super constructor.

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Nail credit, carpet constructor, public savings and the constructor is going to receive a source object

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savings source.

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And once again, this constructor needs to borrow the copy constructor inside of its parent super source.

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OK.

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We'll do the exact same thing inside of loan.

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Public loan, though, receives three parameters.

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When we create a loan object, it needs an ID, a name and a balance.

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And we're going to pass those values into the super constructor, and it's the super constructor that's

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going to beat every field inside of the current object.

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Same thing for the copy constructor.

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And the constructor is going to receive a source object.

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And once again, the scarper constructor needs to borrow the constructor inside of its parent, and

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it's the parent constructor that's going to update every single value inside of the current object.

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And that is wonderful.

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Now, every single child class is capable of upgrading the fields that it inherits.

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What we're going to do is test our code, simply copy these objects from learn the parts.

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All right.

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We should get some areas that's fine.

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We just have to import the classes.

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We can just use auto complete.

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And.

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Should be get to go.

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I'll just add three break points.

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And we'll debug the time.

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So here we're creating an object of the chugging class, the object inherits three fields balance ID

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and name.

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Here we're borrowing the parent constructor.

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And what it does, is it upbeat every single field inside of the current object?

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This the object that was just created.

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All right.

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And here we're creating an object of the savings class, the savings object inherits three fields balance

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ID and name.

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And here we're borrowing the parent constructor that's going to update every single field inside of

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the current object.

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This.

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All right, everything is looking good so far.

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Error creating an object of the loan class.

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The constructor receives three parameters.

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String ID, string name, double balance, we're passing these parameters into the parent constructor,

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and the parent constructor is going to update every single field inside of the current object.

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All right.

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And we're left with three account objects checking savings and loan.

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This is the beauty of inheritance, we only had to define this constructor and this can't be constructor

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once, and we borrowed it inside of every single child class instead of redefining the same thing over

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and over.

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That's why inheritance promotes code reusability.

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All right.

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So we just confirmed that each child is using the parents constructor to in its fields.

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And if you want feel free to test the copy constructor, I'm just going to move on to the final task,

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which is to going back on learning the part.

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We need to add this to string method.

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And now you might think to add a tutoring method inside of each class, like checking savings and loan.

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So here inside checking, you might think to say you might think to just override you string copy over

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the format from learning the parts.

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Here we can say this stark class.

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Start, get simple name.

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Super dont get it.

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Superdog get name.

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Super don't get balance.

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And that's fine and all, but think about savings and loan, they're all just open up a tab for savings.

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Think about savings and loan.

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They share the exact same fields as checking, so you can literally just copy and paste the two string

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method for loan and savings.

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We can say we can copy this over here.

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We should get no errors because it shares the exact same fields and copy this over here.

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But you know how I feel about copying and pasting code, if you can avoid it, please do.

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Instead of redefining that seem to string method three times, every child can just inherit that method

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from its parent.

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So you can delete this method here.

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Actually, it will delete it in every single child.

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And re copy the format inside of account Dogefather.

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He will say this.

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Get class, die, get simple name.

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This start get ID.

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They start get name.

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And this does get bouts.

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We're going to be using that to string in the parent class to get the class name of the current object,

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the idea of the current object, the name of the current object and the balance.

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This is much better because now every child class automatically inherits this tutoring method.

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So back in Maine, we can test this out by just starting off with three print statements.

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Six out.

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Since it's incessant.

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And I'll just print the two string that's inherited by checking.

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Savings and loan.

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OK.

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Move these three break points at three break points right here.

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Here we can see our checking object is calling the two string method inside of its parent account.

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And to string it returns every field inside of the current object.

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Perfect.

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We'll skip over the rest and everything works out perfectly.

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All right, now, your final task was to quality control, just because you can never assume that the

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data being passed in is perfect.

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There might be something wrong, and if one of these lines ends up being faulty, you want to throw

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some kind of exception to force the caller to fix their code and handle such an event.

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So inside the constructor?

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We'll check if the ID being passed is null or a blank, if I.D. is equal to no.

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Or I'd die is blank.

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We'll check if the name is Nola Blank.

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Name is equal to no.

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Or name die is blank.

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And if one of these is true, then we need to throw an illegal argument exception.

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Throw new a legal argument exception, invalid params notice that I'm throwing the exception only once

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here instead of throwing it three different times inside of each child.

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It's much more effective to do it once inside the parent, because every child is eventually going to

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just call the parent constructor.

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Now we can quality control the Centers on Quality Control said it.

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So I'll say if.

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I.D. is equal to no.

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Or if I'd.

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Is blank.

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Throw a new illegal argument exception.

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Invalid ID.

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Same thing inside that name, if name is equal to nil or named is blank.

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There are new a legal argument exception, invalid name.

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OK, and now if the caller tries to pass on any bad values, our app is going to throw an exception,

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forcing them to improve their code.

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And that's all for part two.

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I'll see you soon.