CS 102
Object Oriented Programming
this
this
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¨ An important keyword used inside methods in order
to refer to the current object.
¨ this is “the calling object”
¤ this is the object which called the method
¤ The object that occurs before the dot
Ozyegin University - CS 102 - Object Oriented Programming
this
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¨ There are several use cases of this
Ozyegin University - CS 102 - Object Oriented Programming
Bank Account
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Ozyegin University - CS 102 - Object Oriented Programming
Bank Account
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Ozyegin University - CS 102 - Object Oriented Programming
this
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¨ There are several use cases of this
1. It is used to access the instance variables without any
confusion with parameter names.
Ozyegin University - CS 102 - Object Oriented Programming
this
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¨ There are several use cases of this
1. It is used to access the instance variables without any
confusion with parameter names.
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ One letter parameters are not very descriptive.
¤ It is usually the convention in Java to use the instance
variable name as parameters in the corresponding set
methods.
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ It should be smt like:
¤ parameter names are same with class instance names
¤ no compile error
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ What should
be the output?
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ What should
be the output?
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ It gives warning as : The assignment to variable
interesRate has no effect.
¨ When class instance and parameter have the same
names, the assignment operation has no effect
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ The parameters interestRate and currency shadow
the class instances.
¨ The interestRate assigns the parameter interestRate
to itself, causing no change what so ever.
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ The parameters interestRate and currency shadow
the class instances.
¨ In such cases you can use the this keyword to reach
the class instances.
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ What should
be the output?
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ What should
be the output?
Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ It can be also used
inside constructors
to seperate class
instances from
parameters.
Ozyegin University - CS 102 - Object Oriented Programming
First Constructor
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Ozyegin University - CS 102 - Object Oriented Programming
Second Constructor
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Ozyegin University - CS 102 - Object Oriented Programming
Third Constructor
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Ozyegin University - CS 102 - Object Oriented Programming
this (first use case)
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¨ To be consistent, the same can be done in get
methods.
Ozyegin University - CS 102 - Object Oriented Programming
A conceptual model for this account1
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¨ A conceptual model for
understanding this
number
¨ Each object in Java has an 1
implicit instance variable,
balance
named this, that points to
100
the object itself.
currency
“TL”
this
Ozyegin University - CS 102 - Object Oriented Programming
A conceptual model for this account1
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¨ This is not what really
happens during execution.
number
¨ In Java, each object does
NOT keep a reference to 1
itself – that would be a balance
waste of memory space. 100
¨ However, take this as simply currency
a conceptual model “TL”
that helps us understand this
what this means.
Ozyegin University - CS 102 - Object Oriented Programming
this
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¨ There are several use cases of this
1. It is used to access the instance variables without any
confusion with parameter names.
2. It can be used to invoke constructors of the same class.
Ozyegin University - CS 102 - Object Oriented Programming
this (second use case)
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¨ When you have multiple constructors, this keyword
can be used to call other constructors.
Ozyegin University - CS 102 - Object Oriented Programming
Three Constructors
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Ozyegin University - CS 102 - Object Oriented Programming
this (second use case)
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Ozyegin University - CS 102 - Object Oriented Programming
this (second use case)
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Ozyegin University - CS 102 - Object Oriented Programming
Using this for constructor call
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¨ The constructor call should be the first statement in
your constructor.
¨ Otherwise you will receive the following error!
Ozyegin University - CS 102 - Object Oriented Programming
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¨ You cannot use the constructor of the class inside a
constructor to call another constructor.
¨ The only way of calling another constructor within a
constructor is through using this keyword.
Ozyegin University - CS 102 - Object Oriented Programming
Ozet
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¨ this:
¤ Class instancelarini
(member degiskenlerini),
fonksiyon parametreleri
ile karistirmamak icin.
¤ Constructor in icerisinde
diger bir constructori
cagirabilmek icin.
n Bu durumda cagiran
constructorin ilk cumlesi
“this….“ olmak zorunda
yoksa hata verir.
Ozyegin University - CS 102 - Object Oriented Programming
33 Any Questions ?
Ozyegin University - CS 102 - Object Oriented Programming
