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Well done!
You have completed Intermediate C#!
You have completed Intermediate C#!
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All objects can be converted to a string using ToString. We get to decide what we want that conversion to be.
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The first virtual method we'll
want to know about is ToString.
0:00
This is a very handy method for
a couple of reasons.
0:04
To get to know this method,
let's go into the C# REPL.
0:07
Let's create an empty class named Shoe.
0:12
Because Shoe inherits from System.Object,
it has the ToString method.
0:18
ToString is an instance method, so
0:24
we'll need to create an instance of Shoe,
and now we can call ToString on it.
0:27
ToString just returned a string that
contained the name of the class.
0:34
Let's create an instance of
the System.Random class, and
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call ToString on it.
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Again, it returns the name of the class.
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The full name of the Random
class is System.Random,
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because it's in the System namespace.
0:51
The actual type name for
an int is System.Int32.
0:53
We can know that by calling
GetType on an integer instance.
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Let's say 5.GetType().
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Remember, I said that all types
inherit from System.Object.
1:05
This includes numeric types like int and
double.
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This means we can call any of the methods
provided by System.Object such as
1:13
GetType and ToString on any object in C#.
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Now let's call ToString on
the number 5 and see what we get.
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We get the string 5.
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You might have expected us to
get System.Int32 as our string,
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just like we did with the Random class and
the Shoe class.
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The reason we didn't is
because the integer type
1:37
has overridden the ToString method and
provided its own implementation.
1:42
Instead of returning System.Int32,
1:47
it converts the value stored in
the object to a string and returns that.
1:49
Being able to override
ToString is very beneficial.
1:54
For example, the concatenation operator
provided by the String class calls
1:58
ToString on its operands.
2:03
If we took a string and
concatenated it with an integer,
2:04
the concatenation operator here,
which is this plus,
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first calls ToString on the integer 5 and
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then appends the resulting string
to the end of A, and we get A5.
2:18
Because all types inherit from
System.Object and therefore all have
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a ToString method, the concatenation
operator can work with any object.
2:29
Let's use this feature to improve
the Treehouse Defense game.
2:34
In the constructor of MapLocation,
2:39
we do this check to see if
the coordinates are on the map.
2:42
If they aren't,
we throw this OutOfBoundsException.
2:45
In the exception message,
we have this x +,
2:49
+ y + is outside
the boundaries of the map.
2:53
It seems to me that we can streamline
this a bit so that this just says,
2:57
this is outside the boundaries of the map.
3:02
Now, over in the Point class,
we can override the ToString method.
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So we'll say public
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override string ToString.
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And in here, we'll
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just return x +, + y.
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Now over in the tower's
FireOnInvaders method,
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let's change this message to say,
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Neutralized an invader
at invader.Location.
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Now let's compile this to
see how the output changes.
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And run it.
4:02
See, here now it says,
neutralized an invader at 2,2.
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Now we don't have to write x,y everywhere
that we want to print a location.
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And the code is more succinct and
readable.
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This works even though the concatenation
operator doesn't know about our
4:20
Point class.
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That class we wrote ourselves.
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All it knows about is System.Object.
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There are lots of methods and
4:29
operators that need a string
representation of an object.
4:30
Overriding System.Object's ToString
method allows us to
4:34
provide whatever string we want.
4:37
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