Java Programming Tutorial - 53 - ActionListner Video Lecture - Java Programming

what is going on guys welcome to your
53rd java tutorial and this is pretty
much a continuation of the 50 second one
and there's probably going to be a fifty
fourth one but i'm just a real quick
view what we did pretty much already if
you didn't watch 52 for some reason we
just built a window and put four things
in it and that's a that's pretty much it
and now what we're going to do is pretty
much add some functionality to this and
what we're going to say is all right
when you enter text and one of those
text fields and press Enter
what we wanted to do is pop up another
box saying what you entered like when a
user would type in something and it says
like a verification or something so
let's get right to it now what we need
to do is the first thing that we're
going to do is build an action listener
object so what this means is we have
four text fields
waiting on the screen and they're pretty
much dumb and they don't do anything
right now what we want them to do is to
add some brains to them and have them
waiting on the screen in listening it's
called and when you listen you're pretty
much just waiting for an event to happen
so right now they just look pretty
they're not even waiting for anything so
what we want to say is all right text
boxes listen for something to happen and
when that happens we want you to execute
a bunch of code so the first thing that
we're going to need to do is we're going
to build another class to execute the
code but this class I'm going to build
an object for this class before I even
build the class so the class name is
going to be the handler and we're going
to get some errors right here but that's
fine and I'm just going to name my
object handler and this is going to be
equals new handler class and if you're
saying all right where is this handler
class we didn't build it yet but I will
we promise
so actually hold on new the handler
there we go and what this does is it
pretty much builds an action listener
object so now we're going to make a new
class later on arm that you'll see what
this does later but what we need to do
is add this
object to each of the items so item one
what we need to do is add action
listener and what this takes as an
argument is the object we just created
so that's why we need to do that and the
object you can see it is called handler
so handler right like that and we need
to do this for each object so let's go
ahead and copy this copy and paste paste
I'm - I'm three and of course our
password which is password field right
there and add add action listener and
this is of course going to take the
handler argument again so now we have an
object of the class the handler which we
didn't make it but that's what we're
going to do right now so once you uh let
me make sure
here's jframe here's the one class
here's where one class ends or pretty
much our constructor and now here's
another thing I'm going to tell you um
this pretty much whole thing is our
constructor which is pretty much a
method for um this tuna class and you
probably think in our I'm going to build
a new class I'm going to build it on the
outside of this well actually we're
going to build another class but we're
going to build it inside this tuna class
and when you do that when you build a
class inside the class the class that's
inside inherits all the crap from the
class that's outside so that's what we
want to do so let's go ahead and make
this private because it's no need to
make it public class and I hit insert
class the handler or whatever you named
it right there and now we see we get a
whole bunch of other error messages
implements P implements action
listener and I spelled it there we go
implements action listener now what we
want to do is go ahead and build body
for this and now what we have is our
class and why did we need to name the
handler because that's what the object
was and it implements action listener
and what this means is pretty much that
this is going to be the class to handle
the events and you'll see why later on
but I know it's confusing right now but
what this action listener class is is it
takes one method there's only one method
we're going to be building in this class
and that's the method that's going to be
called automatically whenever an event
occurs and to do that type up lick void
and I know this doesn't make any sense
to you right now it's weird because you
kind of have to build the whole program
and see what's going on but I promise by
the end of this you'll see what's going
on action and you need to name this
performed and as a argument you need to
take action event and then you need to
name your variable something like event
like that and now as well let's go ahead
and start building the body for this so
what happens in this private class right
here is as soon as an event occurs
whatever happens inside here is going to
handle the event so let's go ahead and
type some stuff - um pretty much just
add a body to our method the first thing
we're going to do is build a string
variable and we're just name is string
and set it equal to an empty string and
this is going to be the final string the
outputs but um you know we don't need to
worry about that now now the next thing
we're going to want to do is make pretty
much a huge if statement in you'll see
why in a second the first condition
we're going to test if the event and
remember this is like an enter or a
click and in this case is going to be if
the event is going to be when the Hugh
can't talk when the user presses enter
so if the event equals get
source and the source pretty much means
where it happens if it's equal to item 1
and what this means is pretty much if
they clicked enter on text field number
1 then what do we want to do well the
first thing we're going to want to do it
is take that string variable that is
empty right now and we want to set it
equal to string format and what we just
use C style formatting and we're going
to want to set this equal to put
something like field 1 percent s and put
those in quotation marks so what this is
going to output is field 1 with a
variable right here and as our variable
what we want to do is press event and
this is get action command now this is
the last thing in this tutorial that's
going to confuse it what get action
command means after I added my semicolon
is get the text from that location so if
they type in Bucky and field 1 and press
Enter what this is going to do is say
alright your event source or you hit
enter at item number 1 so what am I
going to do is put field 1 equals Bucky
in you'll see why later on but for now
just follow with me the next thing we're
going to do is build 3 else ifs so else
if and just go ahead and copy this copy
this paste in event to field - and we'll
get the action command for that now
let's go ahead and just copy this one
more time copy make sure my cursor is in
the right spot oh cool it's messing up
cool
I am paste if the vent get sorts equals
from item three then we just want output
field three equals that and now what we
want to do lastly is put else--if and
let's go ahead and put event get source
all right if this events occurs on what
do we name it password field then what
do you want to do set the string while
you mess it up pause set the string
equal to string format and and let's
just go ahead and do the same thing the
format is let's put password field is
percent s and arguments it takes is of
course event get actually in command
right there so now make sure we're good
go don't have any errors decide from
these and what error begin right here
the method add action there is undefined
which is a worry about that later
and the last thing we're going to want
to do I actually am run out I'm so I'll
do in next tutorial in the next tour we
will finish everything up so thank you
guys for watching I'll see you then