programming-for-dummies

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Design Patterns
Three examples of different design patterns (and their unusual names)
include
✦ Interface pattern
✦ Flyweight pattern
✦ Memento pattern
An interface pattern defines an object that simplifies access to something
else. For example, suppose someone has written a library of useful subprograms.
Rather than let other programmers access these subprograms
directly, an interface pattern defines an object to provide access to these
subprograms instead. By doing this, an interface pattern keeps your program
focused on using object-oriented features.
So this library might contain subprograms for displaying graphics and calculating
mathematical equations. You could use the interface pattern to define
one object for accessing the graphics subprograms and a second object for
accessing the mathematical equations subprograms, as shown in Figure 7-10.
Library of subprograms
Figure 7-10:
An interface
pattern
provides an
objectoriented
interface
to a nonobjectoriented
item, such
as a library
of subprograms.
Object One
Graphics subprograms
Math subprograms
Object Two
Subprogram Graphics 1
Subprogram Graphics 2
Subprogram Graphics 3
Subprogram Graphics 4
Subprogram Math 1
Subprogram Math 2
Subprogram Math 3
A flyweight pattern is used to create multiple objects. For example, you could
create a word processor with every character defined as an object that contains
formatting information, such as font, font size, underlining, and so on.
However, a typical word processor document would contain thousands of
objects (characters), and because each object gobbles up memory, creating
so many objects would likely swamp the computer’s memory.