C# 4 and .NET 4

228 ❘ ChaPTer 10 cOllectiOns
}
{
}
int compare = this.LastName.CompareTo(other.LastName);
if (compare == 0)
return this.FirstName.CompareTo(other.FirstName);
return compare;
code snippet ListSamples/Racer.cs
Creating lists
You can create list objects by invoking the default constructor. With the generic class List, you must
specify the type for the values of the list with the declaration. The code shows how to declare a List
with int and a list with Racer elements. ArrayList is a non-generic list that accepts any Object type for
its elements.
Using the default constructor creates an empty list. As soon as elements are added to the list, the capacity
of the list is extended to allow four elements. If the fifth element is added, the list is resized to allow eight
elements. If eight elements are not enough, the list is resized again to contain 16 elements. With every resize
the capacity of the list is doubled.
var intList = new List();
var racers = new List();
If the capacity of the list changes, the complete collection is reallocated to a new memory block.
With the implementation of List, an array of type T is used. With reallocation, a new array is
created, and Array.Copy() copies the elements from the old to the new array. To save time, if you
know the number of elements in advance, that should be in the list; you can define the capacity
with the constructor. Here a collection with a capacity of 10 elements is created. If the capacity
is not large enough for the elements added, the capacity is resized to 20 and 40 elements —
doubled again.
List intList = new List(10);
You can get and set the capacity of a collection by using the Capacity property:
intList.Capacity = 20;
The capacity is not the same as the number of elements in the collection. The number of elements in the collection
can be read with the Count property. Of course, the capacity is always larger or equal to the number
of items. As long as no element was added to the list, the count is 0.
Console.WriteLine(intList.Count);
If you are finished adding elements to the list and don’t want to add any more elements, you can get rid of
the unneeded capacity by invoking the TrimExcess() method. However, because the relocation takes time,
TrimExcess() does nothing if the item count is more than 90 percent of capacity.
Collection initializers
intList.TrimExcess();
You can also assign values to collections using collection initializers. The syntax of collection initializers
is similar to array initializers, which were explained in Chapter 6. With a collection initializer, values are
assigned to the collection within curly brackets at the initialization of the collection:
var intList = new List() {1, 2};
var stringList = new List() {"one", "two"};
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