C# 5.0 Programmer's Reference

Stacks and Queues ❘ 331
}
}
jobsListBox.Items.Add(Jobs.GetKey(i) + ": " + Jobs.GetByIndex(i));
Enter a job name, select a priority, and click Add. The program adds the new job to the SortedList
and calls the ListJobs method to list the jobs in their sorted order.
The ListJobs method loops through the indices of the items in the list and displays their keys
and values.
A SortedList is more complicated (and hence slower) than a Hashtable or an array, so you should
use it only if you need its special properties.
CollectionsUtil
Normally, Hashtables and SortedLists are case-sensitive. The CollectionsUtil class provides two
shared methods, CreateCaseInsensitiveHashtable and CreateCaseInsensitiveSortedList,
which create Hashtables and SortedLists that are case-insensitive.
If you can use case-insensitive Hashtables and SortedLists, you may be better off using them
because they will prevent the program from accidentally adding the same item twice with different
capitalization.
Stacks and Queues
Stacks and queues are specialized data structures that are useful in many programming applications
that need to add and remove items in a particular order. The .NET Framework Stack and Queue
classes implement stacks and queues.
The difference between a stack and a queue is the order in
which they return the items stored in them. The following
two sections describe stacks and queues and explain the
ways in which they return items.
Stack
A stack returns items in last-in-first-out (LIFO, pronounced
life-o) order. Because of its LIFO behavior, a
stack is sometimes called a LIFO list or simply a LIFO.
Adding an item to the stack is called pushing the item
onto the stack and removing an item is called popping
the item off the stack. These operations have the names
push and pop because a stack is like a spring-loaded stack
of plates in a cafeteria or buffet. You push new plates
down onto the top of the stack and the plates sink into the
counter. You pop the top plate off and the stack rises to
give you the next plate. Figure 14-4 illustrates this kind
of stack.
Push
Pop
Figure 14-4: A Stack lets you remove
items in last-in-first-out (LIFO) order.
www.it-ebooks.info