Design Pattern Overview
Q:What does a pattern do?
A:Documents a recurring重复出现的 problem/solution paring within a given context

Essential elements

Pattern name

• Used to provide a single and meaningful name to the pattern which defines a design problem and a solution for it.
• Naming a design pattern helps itself to be referred to others easily.
• Allows easy documentation
• Right vocabulary word makes it easier to think about the design.

Problem

• An abstract description.
• Describes when to apply the pattern.
• Explains the context.
• Might describe specific design problems such as how to represent algorithms as objects.
• Might describe a class or object structures that are symptomatic of an inflexible design.
• Sometimes the problem will include a list of conditions that must be met before it makes sense to apply

Solution

• describes the elements that make up the design, their relationships, responsibilities, and collaborations协作.
• Not the complete code, but it works as a template which can be fulfilled with code.
• Abstract description of the problem and how a general arrangement of elements (classes and objects in our case) solves it.

Results and consequences of applying the pattern.

• The consequences for software often concern space and time tradeoffs.
• They may address language and implementation issues as well.
• Reuse is an important factor in object-oriented design
• So, consequences of a pattern include its impact on a system’s flexibility, extensibility, or portability.
• Listing these consequences explicitly helps you understand and evaluate them.

Patterns

Solutions drawn from experience that were then documented.