Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
By overriding Object.Equals we get to decide what it means for two objects to be equal to each other.
So, how can we check if two different
map location objects represent the same
0:00
location on the map?
0:04
If we go to the documentation for
0:06
system.object we'll find
a method named Equals.
0:08
This is the method that is called
to determine if two objects
0:12
are practically equal.
0:15
By default, it just calls
the ReferenceEquals method to see if two
0:17
objects refer to the same object but
we can override this behavior.
0:21
Let's do that in the point class and map
location will inherit this new behavior.
0:25
So we can overwrite equals to return true
0:31
if the coordinates of
the two points are equal.
0:33
So we'll say public override.
0:36
Equals and
equals takes a parameter of type Object.
0:42
We can type system.object or
we can just type object.
0:47
System.object is the actual
name of the object class.
0:52
Object with the lowercase o is
just an alias just like int
0:57
actually refers to System.int32.
1:02
We'll call our parameter obj.
1:05
The first thing we need to do is to
make sure that the object passed in
1:09
is in fact of type point.
1:13
So we can say if(!(obj is Point))
1:16
then, Will return false.
1:22
Because if the object passed in,
isn't a point,
1:29
they can't possibly equal each other,
now can they?
1:32
Using the is operator also has the nice
effect of checking to make sure
1:35
that it isn't null either.
1:40
Because if obj is null, then this
obj is point will also return false.
1:42
Now that we know that they are the same
type, we need to cast obj to a point.
1:50
We'll call it that.
1:57
Now we can return true if this .X.
2:01
Equals that .X.
2:05
And this .Y.
2:10
equals.
2:13
That .Y.
2:14
Now let's go back to
the Is.OnPath method and
2:15
change this from using the equality
operator to using .Equals.
2:19
We do this because we don't want to check
if the objects are the exact same object.
2:29
We just want to check to see if they
are same for all intents and purposes.
2:35
That is, they refer to the same
coordinates on the map.
2:39
Unless we really want to check if two
variables refer to the exact same object,
2:42
we should always use equals
instead of the equality operator.
2:47
The caveat to this rule is when dealing
with numeric types and strings.
2:50
In the case of strings and
numeric types like int and double.
2:55
The equality operator
will always return true
2:58
if the objects contain the same value.
3:01
So when dealing with strings,
ints, and doubles.
3:04
We can always use the equality operator.
3:07
And it will have the same
result as if we called equals.
3:09
Let's compile and run our program to see
if the Is.OnPath method works as expected.
3:13
Now.
3:17
Yay!
We get our message printed out so
3:19
it works as expected, but
what does this compiler warning here?
3:22
This is telling us that if
we override object.equals
3:28
we should also override
object.GetHashCode.
3:32
We'll learn about the GetHashCode
method in the next video.
3:36
You need to sign up for Treehouse in order to download course files.
Sign up