programming-for-dummies

366
Using Queues
A queue gets its name because the data structure resembles a line of waiting
people, such as a line at a bank teller. The first person in the line (queue) is
also the first person who gets to leave the line. As a result, a queue is often a
First In, First Out (FIFO) data structure, as shown in Figure 4-4.
New data gets added to the end of the queue.
Data #4
Data #3 Data #2 Data #1
Figure 4-4:
The queue
data
structure
mimics a
line of
people.
Data #4 Data #3 Data #2 Data #1
Data #4 Data #3 Data #2
Data #1
Old data gets removed from the front of the queue.
Like a stack, a queue can expand and shrink automatically, depending on the
amount of data you store in it. Unlike a stack that only lets you store and
retrieve data from the top, a queue lets you store data on one end but
remove that data from the opposite end.
Most programming languages don’t offer the queue data structure as a
built-in feature. Instead, you have to create a queue with other data structures,
such as an array or a linked list, to create an abstract data structure.
Fortunately, many programming language compilers come with libraries (or
classes in object-oriented languages) of subprograms that have created the
queue data structure for you.
Because a queue is just a data structure, you can declare a variable to represent
a queue in Visual Basic.NET by doing the following:
Dim LongLine as New Queue
This command simply identifies a LongLine variable as a queue data structure.
The New command tells the computer to create a new stack.