Back-End Programming Exam > Back-End Programming Videos > Java Programming Fundamentals: For Beginners > Java Programming Tutorial - 43 - Composition
Java Programming Tutorial - 43 - Composition Video Lecture | Java Programming Fundamentals: For Beginners - Back-End Programming
FAQs on Java Programming Tutorial - 43 - Composition Video Lecture - Java Programming Fundamentals: For Beginners - Back-End Programming
| 1. What is composition in Java programming? |  |
Ans. Composition in Java programming is a design technique that allows objects to be composed of other objects. It is a way to create complex classes by combining simpler classes as their components. This is achieved by creating an instance of one class within another class and using it as a member variable. Composition promotes code reusability and modularity.
| 2. How is composition different from inheritance in Java? | |
Ans. Composition and inheritance are both object-oriented programming techniques in Java, but they serve different purposes. Inheritance allows a class to inherit properties and behaviors from another class, creating an "is-a" relationship. Composition, on the other hand, creates a "has-a" relationship by combining objects. While inheritance is useful for creating hierarchical relationships, composition provides more flexibility and allows for better code organization and encapsulation.
| 3. Can a class have multiple compositions in Java? | |
Ans. Yes, a class can have multiple compositions in Java. This means that a class can contain multiple instances of other classes as member variables. These member variables can be used to represent different aspects or components of the class. For example, a Car class can have compositions such as an Engine, Wheels, and Seats, each represented by a separate instance of a class.
| 4. How does composition promote code reusability in Java? | |
Ans. Composition promotes code reusability in Java by allowing the reuse of existing classes as components in new classes. Instead of duplicating code or inheriting from a specific class, composition allows for the creation of flexible and modular classes. By reusing existing classes, developers can save time and effort in writing new code and ensure that any changes or improvements made to the reused classes are automatically reflected in the composed class.
| 5. What are the advantages of using composition in Java programming? | |
Ans. There are several advantages of using composition in Java programming:
- Code reusability: Composition allows for the reuse of existing classes as components, promoting code reusability and reducing duplication.
- Flexibility: Composition provides more flexibility than inheritance, as objects can be combined in different ways to create complex classes.
- Modularity: Composition allows for better code organization and encapsulation, as classes can be composed of smaller, more focused components.
- Easy maintenance: With composition, changes or improvements made to the reused classes automatically reflect in the composed class, making maintenance easier.
- Reduced dependencies: Composition reduces class dependencies, making the code more modular and easier to test and debug.
Text Transcript from Video
what's up guys welcome to your 43rd java
tutorial and in this tutorial we're
going to be building the rest of our
program and I'm going to be teaching you
guys about something called composition
now what composition means is that it
means that a class and this is the one
we're going to be building today instead
of just the variables and methods it can
also have references to other objects
for other classes and it could uh
well I'll show you guys what it means so
go ahead in our toon class again in the
last story we built this Popeye class in
our tuna class just clear everything out
and we're going to have two um members
for now go ahead and type private string
and this is a new one name and that's
going to be used just to store my name
or something and we're going to also
have a reference to another class the
potpie class so go ahead and type
private potpie and type birthday since
this program is just going to output my
name and the birthday but it's going to
do in cool way so now that we have two
members of this class right here we have
a new name variable and we have a
reference to a Popeye object or object
so let's go ahead and well let's use it
so the first thing we want to do is
build our constructor so this class is
named tuna so we have to name our method
tuna and that's constructor what this
constructor is going to take is two
arguments it's going to first take that
string variable that we have and we'll
just name it the name so we don't forget
and we also want a reference to our pot
pie date object so let's go ahead and
put pot pie and let's go ahead and write
the date or you can write the birthday
or something like that and now in the
body of our constructor let's just go
ahead and set name set equal to the name
and this go ahead and set birthday that
we declare it up here and set it equal
to the dates so now we are in sync we
are good to go but what we wanted to do
now is go ahead and make another two
string method so let's go ahead and put
public string to string and just like we
did in the potpie class and this method
it's going to take no arguments and for
the body we want to return a string of
course so string format in for our
format I really like when it fills it in
for you you know I want to do the work
myself and in our format just go pull my
name it is % s and that's going to fill
in your name and then let's go ahead and
put my birthday is percent s and here's
work is kind of tricky name birthday so
now if you guys can understand the next
thing I'm about to say you'll understand
um the next thing I'm about to say
sounds easy enough but you understand
the key concept of this tutorial so now
whenever we call whenever we need a
string representation of this what we're
going to do is this it's going to return
my name is and it's going to look right
here to see what it wants to fill in for
name well the name was up here and it's
going to be whatever we gave it passed
it in but for birthday there isn't a
really string name birthday birthday is
just a reference to the date object and
again what this means since it's a
reference to an object and not a string
any time it needs a string from an
object it's going to say alright anytime
you need a string and I'm only object
I'm not a string maybe I can help you
out well I'll go to my class and I'll go
two two string method and then I can
give you the information that you need
so when I put percent s right here you
don't necessarily need to pass in a
string object or excuse me a string
variable what you can do is pass in an
object instead and whenever it looks in
that class it implies through via the
two string method that this is the
string you're looking for so again you
can do two things when you're using this
you can either pass in a regular string
which is just like a bunch of letters or
you can pass in an object and whenever
you do pass in an object it looks into
that class and it looks to the two
string method of that class so that's
two different ways when you're using the
print format that you can do that so now
that we got a two string method which is
pretty much the string representation of
an object in the tuna class and we got a
string representation of an object in
the potpie class I think we're ready to
build some actual objects now put them
to use so go over in your main Bucky or
I don't know whatever you named it and
let's go ahead and build some more
objects one more to be exact so now that
we already build one from Popeye we
probably don't even need that anymore
but we'll keep it up for good looks what
we want to do is build one for tuna so
tuna tuna ooh got the hiccups tuna
object make sure I typed everything or I
got the hiccup in between there and new
tuna and now we need to pass in two
variables again this is going to take
two parameters because look our
constructor takes two parameters it
takes a name and it takes an object so
for the name let's go ahead and pass in
Greg and for the object let's go ahead
and pass an object that we just built
right here so in order to see what
parameters it takes look in your tuna
constructor and you can see it takes a
string and it takes an object well our
string is Greg that's my real name
and our object is pot object and we just
build it up here now everyone knows my
real name oh great so now let's go ahead
and just output what we did
so system.out.print line and let's go
ahead and just write una object but we
have to spell array and we better change
that to Bucky for good looks and now
oh let's see it should be good to go so
let me run this see how many errors I
got and then I'll talk you through one
last time what we did it says my name is
Bucky birthday four or five six you got
it so in the first line in line number
three we built a constructor in the
second line we built a tuna object well
I guess we built objects and both lines
but here's what that you already you
guys already know this one did from last
toriel and for the tuna object when we
build it in the constructor we passed in
two arguments my name in this object
right here
it took the name and set it equal to
name and it took the object and set it
equal to birthday and then it says re
just return it in a string format well
my name is Bucky easy enough my birthday
is this object and it says all right how
am I going to turn an object into a
string well anytime I want to turn an
object into a string I just go to that
class and go to the two string method so
again I'm going to repeat at any time
you want to turn an object in the string
it looks to that class in the two string
method so that is your quick tutorial on
what the two string method is and also
again like I said this is called
composition and that's referring to
objects I'm going to show you guys
that's referring to objects in other
classes as members so this was
composition right here so thank you guys
for watching let's see how much time I
got
oh just in time so thank you guys for
watching make sure to check out my
next tutorial get out of my white house
and make sure subscribe my channel
because you know especially I'm lever so
I'll see you later
tutorial and in this tutorial we're
going to be building the rest of our
program and I'm going to be teaching you
guys about something called composition
now what composition means is that it
means that a class and this is the one
we're going to be building today instead
of just the variables and methods it can
also have references to other objects
for other classes and it could uh
well I'll show you guys what it means so
go ahead in our toon class again in the
last story we built this Popeye class in
our tuna class just clear everything out
and we're going to have two um members
for now go ahead and type private string
and this is a new one name and that's
going to be used just to store my name
or something and we're going to also
have a reference to another class the
potpie class so go ahead and type
private potpie and type birthday since
this program is just going to output my
name and the birthday but it's going to
do in cool way so now that we have two
members of this class right here we have
a new name variable and we have a
reference to a Popeye object or object
so let's go ahead and well let's use it
so the first thing we want to do is
build our constructor so this class is
named tuna so we have to name our method
tuna and that's constructor what this
constructor is going to take is two
arguments it's going to first take that
string variable that we have and we'll
just name it the name so we don't forget
and we also want a reference to our pot
pie date object so let's go ahead and
put pot pie and let's go ahead and write
the date or you can write the birthday
or something like that and now in the
body of our constructor let's just go
ahead and set name set equal to the name
and this go ahead and set birthday that
we declare it up here and set it equal
to the dates so now we are in sync we
are good to go but what we wanted to do
now is go ahead and make another two
string method so let's go ahead and put
public string to string and just like we
did in the potpie class and this method
it's going to take no arguments and for
the body we want to return a string of
course so string format in for our
format I really like when it fills it in
for you you know I want to do the work
myself and in our format just go pull my
name it is % s and that's going to fill
in your name and then let's go ahead and
put my birthday is percent s and here's
work is kind of tricky name birthday so
now if you guys can understand the next
thing I'm about to say you'll understand
um the next thing I'm about to say
sounds easy enough but you understand
the key concept of this tutorial so now
whenever we call whenever we need a
string representation of this what we're
going to do is this it's going to return
my name is and it's going to look right
here to see what it wants to fill in for
name well the name was up here and it's
going to be whatever we gave it passed
it in but for birthday there isn't a
really string name birthday birthday is
just a reference to the date object and
again what this means since it's a
reference to an object and not a string
any time it needs a string from an
object it's going to say alright anytime
you need a string and I'm only object
I'm not a string maybe I can help you
out well I'll go to my class and I'll go
two two string method and then I can
give you the information that you need
so when I put percent s right here you
don't necessarily need to pass in a
string object or excuse me a string
variable what you can do is pass in an
object instead and whenever it looks in
that class it implies through via the
two string method that this is the
string you're looking for so again you
can do two things when you're using this
you can either pass in a regular string
which is just like a bunch of letters or
you can pass in an object and whenever
you do pass in an object it looks into
that class and it looks to the two
string method of that class so that's
two different ways when you're using the
print format that you can do that so now
that we got a two string method which is
pretty much the string representation of
an object in the tuna class and we got a
string representation of an object in
the potpie class I think we're ready to
build some actual objects now put them
to use so go over in your main Bucky or
I don't know whatever you named it and
let's go ahead and build some more
objects one more to be exact so now that
we already build one from Popeye we
probably don't even need that anymore
but we'll keep it up for good looks what
we want to do is build one for tuna so
tuna tuna ooh got the hiccups tuna
object make sure I typed everything or I
got the hiccup in between there and new
tuna and now we need to pass in two
variables again this is going to take
two parameters because look our
constructor takes two parameters it
takes a name and it takes an object so
for the name let's go ahead and pass in
Greg and for the object let's go ahead
and pass an object that we just built
right here so in order to see what
parameters it takes look in your tuna
constructor and you can see it takes a
string and it takes an object well our
string is Greg that's my real name
and our object is pot object and we just
build it up here now everyone knows my
real name oh great so now let's go ahead
and just output what we did
so system.out.print line and let's go
ahead and just write una object but we
have to spell array and we better change
that to Bucky for good looks and now
oh let's see it should be good to go so
let me run this see how many errors I
got and then I'll talk you through one
last time what we did it says my name is
Bucky birthday four or five six you got
it so in the first line in line number
three we built a constructor in the
second line we built a tuna object well
I guess we built objects and both lines
but here's what that you already you
guys already know this one did from last
toriel and for the tuna object when we
build it in the constructor we passed in
two arguments my name in this object
right here
it took the name and set it equal to
name and it took the object and set it
equal to birthday and then it says re
just return it in a string format well
my name is Bucky easy enough my birthday
is this object and it says all right how
am I going to turn an object into a
string well anytime I want to turn an
object into a string I just go to that
class and go to the two string method so
again I'm going to repeat at any time
you want to turn an object in the string
it looks to that class in the two string
method so that is your quick tutorial on
what the two string method is and also
again like I said this is called
composition and that's referring to
objects I'm going to show you guys
that's referring to objects in other
classes as members so this was
composition right here so thank you guys
for watching let's see how much time I
got
oh just in time so thank you guys for
watching make sure to check out my
next tutorial get out of my white house
and make sure subscribe my channel
because you know especially I'm lever so
I'll see you later
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Oct 24, 2024 Last updated |
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