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Object.ToString
4:40All objects can be converted to a string using ToString. We get to decide what we want that conversion to be.
The first virtual method we'll
want to know about is ToString.
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This is a very handy method for
a couple of reasons.
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To get to know this method,
let's go into the C# REPL.
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Let's create an empty class named Shoe.
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Because Shoe inherits from System.Object,
it has the ToString method.
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ToString is an instance method, so
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we'll need to create an instance of Shoe,
and now we can call ToString on it.
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ToString just returned a string that
contained the name of the class.
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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.
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The actual type name for
an int is System.Int32.
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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.
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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
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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
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has overridden the ToString method and
provided its own implementation.
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Instead of returning System.Int32,
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it converts the value stored in
the object to a string and returns that.
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Being able to override
ToString is very beneficial.
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For example, the concatenation operator
provided by the String class calls
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ToString on its operands.
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If we took a string and
concatenated it with an integer,
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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.
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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.
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Let's use this feature to improve
the Treehouse Defense game.
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In the constructor of MapLocation,
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we do this check to see if
the coordinates are on the map.
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If they aren't,
we throw this OutOfBoundsException.
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In the exception message,
we have this x +,
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+ y + is outside
the boundaries of the map.
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It seems to me that we can streamline
this a bit so that this just says,
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this is outside the boundaries of the map.
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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.
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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
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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
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operators that need a string
representation of an object.
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Overriding System.Object's ToString
method allows us to
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provide whatever string we want.
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