- 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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Property Initial Values
3:57Just like fields, properties can also have values set upon object creation.
There's one more thing we need
to add to the invader class.
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Invaders can't be invincible.
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As towers shoot and hit them,
they need to be disabled somehow.
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Often times, opponents in games
have a certain amount of health
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that decreases as
the opponent sustains damage.
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We can implement this same
idea in the invader class.
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You know everything you need to know
in order to add this feature to
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the invader class.
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Think about what we'll need to add to
this class in order to implement this.
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You'll probably need some
sort of variable to store
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how much health the invader has remaining.
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Invaders also need to start out
with a certain level of health.
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We'll need to provide some way for
other classes, such as the tower class
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to decrease the health of the invader
if they successfully hit it.
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I suggest you pause the video and
take a moment to think about this and
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even code up your own solution.
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When you come back,
I'll show you how I would do it.
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All right, here in our code
let's work through a solution.
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First.
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I think we should add
a member to the class for
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storing how much health
the invader has remaining.
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We need to decide if this should
be a property or a field and
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what sort of accessibility it should have.
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Maybe we should answer the question
of accessibility first.
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Is it reasonable for
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other classes to be able to see how
much health the invader has remaining?
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I think so.
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So, that means we should make it public.
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Making it public answers our question of
whether to make it a property or a field.
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I mentioned earlier that for a number
of reasons it's best to make public
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member variables properties,
so we'll make this a property.
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I'll call it Health.
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Now, we need to decide what sort
of accessibility the getter and
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the setter of the property should have.
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I already mentioned the other classes
will want to see what the health of
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the invader is.
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So, we should make the getter public.
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Since getters and setters of
a property are public by default,
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we don't need to type public here.
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What about the setter?
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Should other classes be able to
change the health of the invader?
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Well, that's sort of the point of
adding this in the first place, so
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let's keep it public as well.
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Now we need to give the health property
a starting value, otherwise it will
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have a default value of zero, which would
make for a very short lived invader.
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Now there are a couple of ways we
could give it an initial value.
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We could assign it a value here
in the constructor like so and
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give it a starting value of two.
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Or we can just assign it
a value where we declared it.
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In a case like this where the value is
a literal number that isn't passed into
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the constructor, I prefer to
assign it here at the property.
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Now we could actually improve
this interface a little more, and
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encapsulate the health concept even more.
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Let's provide a method
called decrease health.
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That decreases the health
by a passed in factor.
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School type public, void, decrease health.
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And then the parameter is the factor
by which to decrease the health.
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So make that an integer.
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And we'll just say health equals factor.
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Now it's obvious to all
users of this class
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how to decrease the health of an invader.
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Instead of a coder having to assume that
they should alter the health property
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directly, there's a method
called DecreaseHealth.
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This is an example of
self documenting code.
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Self documenting code is code that's so
clear we don't have to write many comments
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or other documentation that
describes how to use it.
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This is usually accomplished
by a well thought out design,
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good encapsulation practices, and
giving things clear descriptive names.
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Now that we're providing
a method to change the health,
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we should make the health
property's setter private
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to make it clear to other coders
that they should use the method.
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