- Accessor Methods 4:33
- Accessor Methods 2 objectives
- Properties 4:22
- Properties 1 objective
- Auto-Properties 4:12
- Auto-Properties 2 objectives
- Using Properties 4:20
- Using Properties 1 question
- Computed Properties 4:19
- Computed Properties 1 objective
- Expression Bodied Members 2:52
- Expression Bodied Members 2 objectives
- Property Initial Values 3:57
- Property Initial Values 1 objective
- Property Practice 5:16
- Properties 4 questions
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Accessor Methods
4:33An encapsulation strategy is to only allow indirect access to fields with getter and setter accessor methods.
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So far,
the invader class is completely empty.
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We can start to code it up now.
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One attribute the invader should
have is its location on the map.
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We need this in order to determine
how close they are to towers,
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to see if they're in range of each other.
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Let's add a MapLocation field to
the invader class and call it Location.
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It'll need to be public so the other
classes can get the invader's location.
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And it can't be read only because
the location changes throughout the game.
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Generally it's a bad idea
to make fields public
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because this exposes too much of
the internal workings of the class.
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In other words,
this is poor encapsulation.
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A better way to go is to make
the Location field private and
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then write public methods
to access the field.
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We'll need two methods.
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One that gets the location and
one that sets the location.
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This pattern is so common in programming
that there are special terms for
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these kinds of methods.
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They're called accessor methods.
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The method that's used to get
the value is called a getter.
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And the method that's used to set
the value is called a setter.
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We'll call the getter GetLocation.
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So I'll say public and
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it will return our MapLocation
cuz that's the type of the field.
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And we'll call it GetLocation.
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And it won't take any parameters because
all it's doing is getting the value
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of the location field and
inside here we'll just return location.
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And I need to change this to underscore
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lowercase l because now
this is a private field.
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For the setter, we'll say public void
because it won't return anything.
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And we'll call it SetLocation and
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it will take a MapLocation
as its parameter.
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And we'll call that value.
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And it will set the value of
_location to the value passed in.
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Now we have a getter and
a setter for the location field.
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At this point you're probably wondering
why we wrote these two methods
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instead of just making
the location field public.
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There are a number of reasons for
using getters and setters.
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For one, it makes it possible to add
code associated with reading and
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writing this field.
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We can now add code inside of these
methods that will be executed
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every time another class attempts
to read or write the location.
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Say for example that we wanted to
make sure that the value parameter
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meets certain conditions before
we change the value of location.
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Or we might want to return something
other than what's stored in location
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under certain conditions.
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Having these methods also
makes debugging much easier.
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There are special programs called
debuggers which we'll learn about
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more in future courses.
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Debuggers can be used to pause
the program before a line is executed.
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The catch is that the line
must be executable.
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Not all lines of code
are considered executable.
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Returning location and assigning location
are both executable lines of code.
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The location field all by
itself is not executable.
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It just represents a place
to store information.
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The line of code we tell the debugger
to stop at is called a breakpoint.
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We can't set a breakpoint
at the location field.
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But, having these two methods gives us
two convenient breakpoint opportunities
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that we wouldn't have if we had
made location a public field.
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A third reason for using getters and
setters is to future-proof the code.
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I know it's hard to imagine right now, but
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someday we might need to change
something about the location field.
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For example, maybe we don't want
the location to be stored in this class.
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We might move it to another class
that this class in turn uses.
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If we were to make a change like that,
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we'd have to fix every other class that
was directly accessing the location field.
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That we wouldn't even have the ability
to fix those other classes
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because they're maintained by other
people who we don't even know.
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There are a few really good reasons for
using getters and
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setters instead of public fields.
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We'll learn more about these reasons
only after we've learned the other two
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principles of object oriented programming,
abstraction and polymorphism.
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