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Hi there.

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Now let's look at an interesting property of inheritance which is called us constructor chaining.

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And at the end of the lesson we will also do a more off concept touching House let's look at the motivation

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for construct searching.

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We know that subclauses inherit methods from superclasses inducement that might depend on supercluster

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.

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That is the instance variables that are defined and superclasses.

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So it means that supercluster it should first be initialized.

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Otherwise you may create an object and when you invoke an inherited method it might not work as expected

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as a state in the superclass is not yet initialized.

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So supercluster it should be initialized first.

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Similarly a superclass might have another superclass and consequently it should also be initialized

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even before the period superclass.

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So basically is subclassed it should be initialized after all its superclass states are initialized

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.

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And that would include the object class to which is a top most superclass.

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And below other constructors are used to initialized it.

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And what does that mean.

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It means that all the superclass constructors should run before the subclass constructor.

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And this is what constructor chaining does.

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We know that when we are creating an object it just runs to construct of code.

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But duplicating the first thing that the constructor does is do in work its superclass constructor which

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in turn calls its own superclass constructor.

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And this process continues on the class objects construct resident and this concept of training process

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happens every single time you create a new object.

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Let's go ahead and look at an example.

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Let's assume we are creating a staff object then the object creation statement would invoke that stops

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constructor unstopped constructor would immediately invoke it superclasses constructor which is the

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user's constructor and then uses constructor would then immediately invoke object classes constructor

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as object as the superclass.

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Off user ones object constructor is run.

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Execution goes back to user constructor and it then picks up at the line following the users in will

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Keeshan to its superclass constructor.

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Similarly once users constructor is completed then the remaining code and stops constructor is executed

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.

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Nobody saw that to invoke superclass methods or hidden fees.

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They could use Superguy work.

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Similarly we can use Superguy word who in work is superclass constructor fathers the Superguy word would

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be followed by parenthesis which mean how zero or more arguments Aspen's kept us going how barometers

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.

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The important thing is the super invocation statement must be a statement in the constructor unless

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at this invocation statement is used.

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Because that doesn't work.

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That statement is useful in working order or that constructors must also be the first statement in the

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constructor.

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So the constructor can how either this in location statement autists opening statement.

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But never bought.

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So if there are multiple overloaded constructors and if they happen to invoke each other than the last

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invoked constructor would be responsible for smoking its superclass constructor.

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So for sure there'll be at least one constructor in a class which does not work.

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Another overloaded constructor that will have a place where invoking the superclass constructor shouldn't

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provide a super and location statement than the compiler.

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So I'd say no odd super invocation statement.

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Again this will be done in the constructor that does not invoke an overloaded constructor.

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So if you consider this use a class which does not have a super and location statement then upon completion

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compiler would add such a super invocation statement as the Fosdike.

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You may also recall that compiler and so it's a not constructor.

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If a constructor is not provided with the constructor actually includes Enno are putting Will Kishan

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statement.

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So if you consider this use it class this does not have a constructor then the compiler would add such

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a nawt constructor which includes a super and location statement.

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Now if for any reason a superclass constructor cannot be invoked then a compiler error is generated

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.

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Here is one example.

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Here we now User class Vittert constructor that takes a single parameter.

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Similarly stuff which is extending user also has a constructor that picks a single parameter.

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Not since but use it on stuff classes already have constructors.

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Compiler will not insert the default nor constructors on this code will give a compiler error because

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compiler will not be able to add in are super in location statement within the staff's constructor as

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there is not before constructor in the User class.

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So there are two things we can do to fix this.

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One is we can write a statement in Wilgus superclass constructor.

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Alternatively we can add a default constructor in the User class and this would allow a compiler to

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insert and no super invocation statement in stuff class.

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So the point is that superclass constructor should be in someway either the programmers should do it

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or the compiler should be able to do it.

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Otherwise you get a compiler error.

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So that's a constructor chaining.

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Let's not do a quick demo.

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Best construct arching could a monster constructor chaining.

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I added some code so I did some Corden's got Java as well as a user not Jela unstaffed or Java.

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We have a concept of how a default constructor which is from one of the previous most and all it is

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doing is re-assigning the user type variable which is defined in User class to stuff and then I just

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introduced this print statement which has been doing stuff constructor run and then I added this new

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constructor an overloaded constructor calls with this stuff and it has a single parameter ID and the

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first statement is invoking the default constructor which is an overloaded constructor so it's invoking

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the default constructor and it is re-assigning the IAB variable to ID it Hardie's an instance variable

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which is defined here and it's employment's this text stuff constructor to an end user and or Java.

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Also added a new constructor.

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It's a default constructor and all it does is it prints this text to use a constructor.

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Now end user test.

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All I'm doing is simply creating an instance of stuff and passing this value treat.

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So basically I'm invoking this constructor.

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This new constructor here and 3 is getting passed here so this is a constructor which is getting invoked

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and but then it will invoke the default constructor in staff and compiler would automatically insert

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the super invocation statement here as we've discussed and so the constructor Newser class would be

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invoked.

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So this statement should be the first one that gets printed and then after that the control comes back

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to here and user types the user gets reassigned to staff and then it prints stuff constructor run after

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that control comes back here to this statement.

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Actually this statement onic reasons ID and then it been stuffed constructor too.

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So let's just go ahead and just run this.

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As you can see the last statement that got brain dead was to use a constructor then Stav constructor

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one unstaffed constructor too so the new action happened this way.

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But then you know it got brain dead and disappeared so that's all because our constructor chaining.

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So we invoked this particular constructor first but the statement here got brain dead last.

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OK so that's because of constructor chaining and that's about it.

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The constructor chain