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In this video we'll see how to use the debugger to investigate our code while it's running!
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When writing a program,
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figuring out what's going on behind
the scenes can be pretty difficult.
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One way to figure out what's going on is
to use print statements like we have here.
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If you're not sure what some variable is
set to, you can just print it out and
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investigate.
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Using print statements is
a great way to debug an app.
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However, IntelliJ also
comes with a debugger
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which lets us walk through
our code one step at a time.
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So instead of running our app like we
have been, let's try using the debugger.
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But first, before we use the debugger,
we need to set a breakpoint in our code.
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A breakpoint is a point in our code where
the debugger will break out of normal
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computation and then wait for
instructions from us on how to proceed.
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It's a stopping point where we can take
our time to look at the current state of
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our app.
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Then, if we want, we can continue
processing the code step by step or
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resume running the app.
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Let's set our first breakpoint on
the first line of the main method.
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We can add breakpoints
in a few different ways.
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First, let's click on the line
we want to add a breakpoint,
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then click on the Run menu, and
select Toggle Line Breakpoint.
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Notice that a little red circle
representing the breakpoint appears
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to the left of this line of code,
this area is known as the gutter.
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To delete the breakpoint, make sure
that the line is still selected and
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then select Run > Toggle Line Breakpoint
to toggle it back off.
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We can also click in the gutter
next to a line of code to add or
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delete a breakpoint, like this.
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We can add breakpoints all over
our code to stop anywhere we like.
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But let's stop with just this one.
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Now to run our app with the debugger, we
want to use the Debug button at the top,
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which is just to the right of the Run
button, and looks kind of like a bug.
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Click it, and once the program starts
it should stop at this breakpoint,
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and open the debug perspective.
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We now have a new debug view
at the bottom of our screen.
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And the line where we inserted our
breakpoint is now highlighted in blue to
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show that this is where
the program stopped.
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Our program is in a paused
state at this point.
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And while it's paused, we can look at
all sorts of things about our code.
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Right now, there's not much to look at.
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This line hasn't been run yet, so the only
variable we have is the args array.
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But if we hover over it, or look to
the right, or even look to the bottom,
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we can see pretty clearly that
args is just an empty array.
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In the next video, we'll step through
our code one line at a time and
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get more comfortable with the debugger.
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