Hello everyone, I am Mr. Programmer - once known as
Canownueasy. This tutorial will show you the uses of ArrayLists in
Java. I will disclose some examples with ArrayLists. This video is
video number 1 in the Using ArrayLists in Java series.
First, I will open the Eclipse IDE. Using the Eclipse IDE is
NOT required - you may choose any IDE (or no IDE) to program. From
personal preferance, Eclipse IDE provides the most amount of features,
and less annoying visual designs and a much faster (and less detailed)
graphical user interface (GUI). On the other hand, the Netbeans IDE
provides a visual Swing Framework IDE.
I'm going to now create a new project. I will title it
"Example". For more information about creating a new project in
Eclipse see my other video.
Let's create a new class "Loader". This class will serve as
the main and only class in the program. Please note, this is JUST an
example class to demonstrate the use of arraylists.
First, let's import the arraylist class. You will notice that
Eclipse underlines it in yellow. This is the result of a WARNING.
Warnings serve to remind developers that their code is dead, not
properly done, and much more. You can compare warnings to grammatical
notices in Microsoft Word which are underlined in green.
Now, we need to make a static main method that accepts
arguments. Any class that has this type of method can serve as the
loader or main class.
Time to create an arraylist. Since we won't have any other
classes in this example project, I am going to make it private.
Private is a Java modifier that only allows limited - or PRIVATE
access to the object. I'm going to call my arraylist "friends".
Inside the semibraces defines the type of fields the arraylist
can contain. I chose String as the list will contain friend's names.
Next, I want to look at options I have to do with my arraylist.
You can always look at options of code by entering a period. Eclipse
uses intellisense and displays what you can do.
For example, I want to add my friend "Johnathan" to the list.
I can do that using the add method.
The add method has an Object parameter. The object must be
the type of field your arraylist can hold. The arraylist can contain
more than one of the same content so I can have 2 "Jonathan" friends.
Let's just say I had an argument with Jonathan, and I'm not
friends with him anymore, I can use the remove method. The same
rules apply for removing as adding.
Every "friend" inside the arraylist is an element. If I were
dealing with cell phone contacts, and I don't remember if I have a
number on the list, I can use the contains method.
The contains method is a boolean. If the list contains an
element equivalent to the contains parameter, it will return true.
Otherwise, it will return false.
If we wanted to find our best friend, we could use the get
method. Arraylists have "slots" that can also be called "compartments".
Each slot has an identification number starting from 0.
I'll create a new String variable and get slot 2 from friends.
Since we don't have 3 friends on our list, I'll add some more friends
"Nathan", "Jimmy", and "Peter".
Let's test our program out.
Nothing happens - well at least that is what appears to the
user. We need to show the user what is going on, so I am going to
print out to the system all the elements or "friends" in the list.
Now, as we see, the console shows the list of friends.
Notice the brackets surrounding the elements. To remove these we
can make a String method that replaces the brackets with nothing
and returns back the new String.
Just modify the code to print out the friends list after
the brackets have been replaced.
We also need to convert the friends to a String.
Now, the console shows the list of friends without the
brackets.
If a user wanted to see which friend is your favorite,
you can print out twice.
The user can now see all of the elements in the list and
see the selected element.
This video is video number 1 in the using arraylists in
Java series.
See the description for captains, thanks.
