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Methods
7:03Methods define an object's behaviors.
[MUSIC]
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So far we've only been modeling
an object's attributes.
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But we also want to define
what an object can do.
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Remember the Pez dispenser example.
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The Pez dispenser has both attributes and
behaviors.
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Pez dispensers have attributes like color,
and how many pieces of Pez are in it.
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Points and maps also have attributes.
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A point's attributes are its x and
y coordinates.
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A map's attributes are its width and
height dimensions.
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The Pez dispenser also has some behaviors.
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It can be refilled.
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It can dispense Pez.
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This is what the Pez dispenser can do.
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In code, objects' behaviors
are defined using methods.
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One of the behaviors we
want our map class to have
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is the ability to determine
if the point is on the map.
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The best way to find that
out is to ask the map
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because the map class is responsible for
the map boundaries.
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To allow the map to answer this question,
we need to write a method.
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Let's add some methods to our classes.
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I've opened up the Map.cs
file in WorkSpaces.
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Let's add a method to
the map class called OnMap.
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The OnMap method will take
a point as a parameter and
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will return true if the point is
on the map and false if it isn't.
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I'll say, public bool OnMap (Point point),
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open curly brace, closing curly brace.
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There we go.
All right,
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as you can see inside
the parentheses of the OnMap method,
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we have a parameter called
point with a lowercase p.
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Which is of type Point
with an uppercase P.
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This is very similar to how we specified
parameters in the constructor.
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Only this time, the point isn't
one of the types built into C#,
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it's one we created ourselves.
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This method will return a value.
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So we specified the return
type as bool here.
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It's a Boolean because this method
will return only true or false.
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Remember, we can write methods
that don't return anything.
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If that was the case,
we would have written void here.
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We'll see some of those later.
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Finally our method needs to be public, so
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that we can call it from
outside of the Map class.
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Now let's write the body of the method.
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Given a point we need to determine if
the point is within the bounds of the map.
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Let's look at an example map again.
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The map has a width of 8 and
a height of 5.
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So all points on this map need to have
an X value that's greater than or
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equal to 0 and less than 8.
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The Y value must be greater than or
equal to 0 and less than 5.
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As you can see every point must
pass these four conditions
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in order to be considered on the map.
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In code, let's start off
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by declaring the variable called inBounds
to hold the return value of our method.
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Now we set this variable equal to the
result of checking our four conditions.
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A point is inBounds if
point.x is greater than or
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equal to 0, and
if point.x is less than Width.
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And if point.y is greater than or equal
to 0, and if point.y is less than Height.
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Finally we'll return the value stored
in inBounds as a return value.
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See how I put two ampersands in
between each of these four conditions?
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This is the conditional and operator.
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The result of an and
operation is true if and
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only if both the left and the right
side of the and operator is true.
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So this expression will only evaluate
to true if X greater than 0 is true and
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X less than Width is true.
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And Y greater than or equal to 0 is true,
and Y less than Height this true.
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If all four of these conditions are true,
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then the entire expression
evaluates to true.
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And inBounds, will be set to true.
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If any of them are false,
then inBounds will be false.
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That's what we want.
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In other words,
if any one of these conditions are false,
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it means the point is outside
the bounds of the map.
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Another conditional operator is or,
which is written as a double bar.
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The result of an or operation is true if
either the left or the right side is true.
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For example if we wanted to check
if the point was out of bounds,
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then we could use the or
operator like this.
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The point is outOfBounds if
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point.X is less than 0 or
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point.x is greater than or equal to Width.
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Or point.y is less than 0, or
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point.y is greater than or
equal to Height.
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Pause the video, and take a minute
to compare these two expressions.
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This will give you a good idea of how
the or operator is different than the and
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operator.
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Then we could check if the point is
inBounds by using the not operator.
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The exclamation mark gives us
the opposite of a boolean.
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It's sometimes called
the boolean negation operator.
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So after adding the not operator,
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if outOfBounds was true,
then it becomes false.
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And if it was false, then it becomes true.
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We could also just negate this entire
expression by wrapping it in parentheses
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and using the not operator
to negate the entire thing.
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Now, both these lines
are equivalent to each other.
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The difference is one's using and,
and the other is using or with a not.
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You might want to pause the video
again to compare these expressions and
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see why this works.
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In the case of the OnMap method, using
the and operator to check of the point is
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inBounds is more straightforward,
so that's what we'll do.
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We'll see more examples of using or,
and and not in the future.
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But I recommend checking
out the teacher's notes for
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more information about
boolean logic in C#.
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Let's take a short break
before we continue analyzing
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the rest of this method.
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