Back-End Programming Exam > Back-End Programming Videos > Java Programming Fundamentals: For Beginners > Java Programming Tutorial - 60 - Array Holding Many Objects
Java Programming Tutorial - 60 - Array Holding Many Objects Video Lecture | Java Programming Fundamentals: For Beginners - Back-End Programming
FAQs on Java Programming Tutorial - 60 - Array Holding Many Objects Video Lecture - Java Programming Fundamentals: For Beginners - Back-End Programming
| 1. What is an array in Java programming? |  |
Ans. In Java programming, an array is a data structure that allows you to store multiple values of the same type in a single variable. It is a fixed-size container that can hold a specific number of elements.
| 2. How do you declare and initialize an array in Java? | |
Ans. To declare and initialize an array in Java, you can use the following syntax:
```java
dataType[] arrayName = new dataType[arraySize];
```
For example, to declare and initialize an array of integers with a size of 5, you can write:
```java
int[] numbers = new int[5];
```
This will create an array called "numbers" that can hold 5 integers.
| 3. How do you access elements in an array in Java? | |
Ans. You can access elements in an array in Java by using the index of the element. Array indexes start from 0, so to access the first element of an array, you would use index 0.
For example, if you have an array called "numbers" and you want to access the second element, you can use the following syntax:
```java
int secondElement = numbers[1];
```
This will assign the value of the second element in the "numbers" array to the variable "secondElement".
| 4. Can an array hold objects in Java? | |
Ans. Yes, an array can hold objects in Java. You can create an array of any type, including objects. For example, if you have a class called "Person", you can create an array of "Person" objects like this:
```java
Person[] people = new Person[5];
```
This will create an array called "people" that can hold 5 "Person" objects.
| 5. How do you iterate over an array in Java? | |
Ans. You can iterate over an array in Java using a for loop or an enhanced for loop (also known as a foreach loop). Here's an example of using a for loop to iterate over an array:
```java
for (int i = 0; i < array.length; i++) {
// access array elements using array[i]
}
```
And here's an example of using an enhanced for loop to iterate over an array:
```java
for (dataType element : array) {
// access array elements using element
}
```
In both cases, you can perform operations on each element of the array within the loop body.
Text Transcript from Video
what is going on guys welcome to my 60th
job tutorial and in the last tutorial we
went ahead and we built a new array and
in essence we built a whole new class to
create this array to hold dog objects
but then it ended tutorial got a little
knock on our door and our boss was like
alright you know how you created that
for dogs
well actually I need you to create one
for fish as well and you know that's
nice and also what can we do what are
our options we can go ahead and create a
new fish list and do this all again or
you know then we're going to have if he
comes back again
and tells us to do it with dolphins or
cats we're going to have to keep doing
that again and again and again so
instead of just having to create class
after class after class I wish there was
way where we can only create one class
and it could hold fish objects and dog
objects and any kind of animal that we
want so then when our boss says alright
I need you to actually create one to
hold um Birds we're going to make oh you
know what already done because we
already built a sufficient and effective
program to hold all classes of animals
even the ones that we didn't even know
um that were created yet so how would we
do that well this dog list is nice but
let's go ahead and delete that right now
delete and okay so instead of just
creating a bunch of different classes to
hold objects let's go ahead and make one
final thing and we're going to name an
animal list so let's go ahead and we can
delete everything out of our main apples
or whatever your main our method is and
now let me get rid of that error and now
let's go ahead and create a new class by
right-clicking source new class and one
go ahead and name this animal list and
this is going to be um pretty much let
me run this so X is annoying me there we
go and this is pretty much going to be
on the class that has our array too
or any type of animal whether it be dog
fish if you decide to create a dolphin
class later if you die decide to create
a hermit class later it's going to
already on be able to hold that so the
first thing that we're going to want to
do is create an array to hold type
animals and remember these dog fish
since they in sixth end animals all of
these are type animals already so let's
go ahead and put private um animal
I didn't yep animal and we'll just name
it list equals new animal five so what
this pretty much means is recreated
array an array name the list and it can
hold five objects of type animal right
there so after let's just go ahead and
make our counting variable perhaps I
equals zero and now we can go ahead and
build I always do that int I equals zero
and now we can go ahead and build our
method and that's public void void we'll
name it
add still but we have to spell void or
right add and we'll put animal a so now
it takes one parameter which is an
animal object and now we'll just do that
test again if what do we name it the
list or actually we want to do if I is
less than the length if I is less than
the list dot length so it would be five
in this case but just in case you change
this then you won't have to change it
each time so that's why I'm doing that
so if I is less than the list length
what do you want to do let's go ahead
and do exact same thing we did last time
the list the index for that which would
be I so at first one I would assign the
list zero set it equal to a which is the
animal object next let's just give us a
little prompt on the screen like
system.out.print line and we'll just
have mo added at
index space plus I so this pretty much
just gives you a little message on the
screen and the last thing we want to do
is increment I because if we don't it's
just going to keep adding to that same
index over and over again so each time
this runs it's going to change that
counter variable that allows us to move
to the next element in our array so now
that we got this animal list it's going
to take any animal object we have and
let's go ahead and I'll show you guys
that right now so in your main class
whatever you named it I named mine
apples still don't know why we can go
ahead and create an animal list object
from this animal list we just created so
let's go ahead and put animal list alo
you can name it whatever you want new
animal list BAM just like that now let's
go go ahead and create a new dog object
because remember that method takes a an
animal object as its parameter so go
ahead and actually you know what I'll do
I'll create a new dog object and a new
fish object so dog will just name it D
because it short and sweet with a new
dog just like that going to put fish
from our fish class create an object
from here F equals new fish like that
now we can go ahead and call the add
method in our alo add first of all we'll
add that dog and I will do a ello add
and now we'll add that fish object so
now if we go ahead and run this you can
see our a animal added at index one this
is the dog object an animal added or
excuse me
animal Atta in the zero this is the dog
object an animal added in next one
that's the fish object right there so
again what we did
real quick overview we created an object
so we can use the methods from this
animal this class we created two objects
of dog and fish which were both animal
type and we go ahead and we just called
the add method so it first added that
dog element to index 0 and add the
element to index 1 and we can call that
five times and then that's it then our
array is full if we call it after that
then it's just gonna it's going to run
the program but it's not going to add it
to our array because it's already full
so this is a much smarter array than we
built last time because now if someone
wants to create a new class that was
like hermit crab like I said before all
they need to do is put extends animal
and it's automatically an animal type so
that way we don't have to create a new
array for dog fish hermit crab dolphin
gopher watch out beavers we just needed
to create this one class right here and
it took care of all those problems so if
you think this array is pretty smart
just wait to the next tutorial we're
going to build this computer program
even smarter and better than this and if
you didn't think that is possible then
trust me just wait to my next tutorial
and one other thing and I know you heard
me before if you watched my last
tutorial my 500th video is going to be
amazing
and it's going to benefit no one but you
guys so um a couple you people might
already know what that means what I'm
hinting at but trust me it's going to be
the best video for you guys ever so
thank you guys for watching don't forget
to subscribe and I will see you next
tutorial
job tutorial and in the last tutorial we
went ahead and we built a new array and
in essence we built a whole new class to
create this array to hold dog objects
but then it ended tutorial got a little
knock on our door and our boss was like
alright you know how you created that
for dogs
well actually I need you to create one
for fish as well and you know that's
nice and also what can we do what are
our options we can go ahead and create a
new fish list and do this all again or
you know then we're going to have if he
comes back again
and tells us to do it with dolphins or
cats we're going to have to keep doing
that again and again and again so
instead of just having to create class
after class after class I wish there was
way where we can only create one class
and it could hold fish objects and dog
objects and any kind of animal that we
want so then when our boss says alright
I need you to actually create one to
hold um Birds we're going to make oh you
know what already done because we
already built a sufficient and effective
program to hold all classes of animals
even the ones that we didn't even know
um that were created yet so how would we
do that well this dog list is nice but
let's go ahead and delete that right now
delete and okay so instead of just
creating a bunch of different classes to
hold objects let's go ahead and make one
final thing and we're going to name an
animal list so let's go ahead and we can
delete everything out of our main apples
or whatever your main our method is and
now let me get rid of that error and now
let's go ahead and create a new class by
right-clicking source new class and one
go ahead and name this animal list and
this is going to be um pretty much let
me run this so X is annoying me there we
go and this is pretty much going to be
on the class that has our array too
or any type of animal whether it be dog
fish if you decide to create a dolphin
class later if you die decide to create
a hermit class later it's going to
already on be able to hold that so the
first thing that we're going to want to
do is create an array to hold type
animals and remember these dog fish
since they in sixth end animals all of
these are type animals already so let's
go ahead and put private um animal
I didn't yep animal and we'll just name
it list equals new animal five so what
this pretty much means is recreated
array an array name the list and it can
hold five objects of type animal right
there so after let's just go ahead and
make our counting variable perhaps I
equals zero and now we can go ahead and
build I always do that int I equals zero
and now we can go ahead and build our
method and that's public void void we'll
name it
add still but we have to spell void or
right add and we'll put animal a so now
it takes one parameter which is an
animal object and now we'll just do that
test again if what do we name it the
list or actually we want to do if I is
less than the length if I is less than
the list dot length so it would be five
in this case but just in case you change
this then you won't have to change it
each time so that's why I'm doing that
so if I is less than the list length
what do you want to do let's go ahead
and do exact same thing we did last time
the list the index for that which would
be I so at first one I would assign the
list zero set it equal to a which is the
animal object next let's just give us a
little prompt on the screen like
system.out.print line and we'll just
have mo added at
index space plus I so this pretty much
just gives you a little message on the
screen and the last thing we want to do
is increment I because if we don't it's
just going to keep adding to that same
index over and over again so each time
this runs it's going to change that
counter variable that allows us to move
to the next element in our array so now
that we got this animal list it's going
to take any animal object we have and
let's go ahead and I'll show you guys
that right now so in your main class
whatever you named it I named mine
apples still don't know why we can go
ahead and create an animal list object
from this animal list we just created so
let's go ahead and put animal list alo
you can name it whatever you want new
animal list BAM just like that now let's
go go ahead and create a new dog object
because remember that method takes a an
animal object as its parameter so go
ahead and actually you know what I'll do
I'll create a new dog object and a new
fish object so dog will just name it D
because it short and sweet with a new
dog just like that going to put fish
from our fish class create an object
from here F equals new fish like that
now we can go ahead and call the add
method in our alo add first of all we'll
add that dog and I will do a ello add
and now we'll add that fish object so
now if we go ahead and run this you can
see our a animal added at index one this
is the dog object an animal added or
excuse me
animal Atta in the zero this is the dog
object an animal added in next one
that's the fish object right there so
again what we did
real quick overview we created an object
so we can use the methods from this
animal this class we created two objects
of dog and fish which were both animal
type and we go ahead and we just called
the add method so it first added that
dog element to index 0 and add the
element to index 1 and we can call that
five times and then that's it then our
array is full if we call it after that
then it's just gonna it's going to run
the program but it's not going to add it
to our array because it's already full
so this is a much smarter array than we
built last time because now if someone
wants to create a new class that was
like hermit crab like I said before all
they need to do is put extends animal
and it's automatically an animal type so
that way we don't have to create a new
array for dog fish hermit crab dolphin
gopher watch out beavers we just needed
to create this one class right here and
it took care of all those problems so if
you think this array is pretty smart
just wait to the next tutorial we're
going to build this computer program
even smarter and better than this and if
you didn't think that is possible then
trust me just wait to my next tutorial
and one other thing and I know you heard
me before if you watched my last
tutorial my 500th video is going to be
amazing
and it's going to benefit no one but you
guys so um a couple you people might
already know what that means what I'm
hinting at but trust me it's going to be
the best video for you guys ever so
thank you guys for watching don't forget
to subscribe and I will see you next
tutorial
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Oct 24, 2024 Last updated |
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