What they are and are not.
WHAT A PATTERN IS
A named, documented solution to a problem that recurs.
WHAT THEY PROVIDE
A vocabulary, so a structure can be named rather than described Solutions that have been examined and refined Awareness of trade-offs already identified
WHAT THEY ARE NOT
Rules Goals Evidence of good design
WHAT THE COMMON MISUSE IS
Applying patterns because they are known, rather than because a problem calls for them.
WHAT THAT PRODUCES
Complexity with no benefit, and code harder to follow than the direct version.
WHAT TO ASK BEFORE APPLYING ONE
What problem am I solving?
WHAT TO DO IF THE ANSWER IS UNCLEAR
Write the direct version.
WHAT PATTERNS ARE MOST USEFUL FOR
Recognising a structure you already need, and naming it.
WHAT THE CATEGORIES ARE
- Creational: how objects are made
- Structural: how objects are composed
- Behavioural: how objects interact
WHAT TO LEARN
The problems they address, more than the implementations.
WHY
The implementation varies by language; the problem does not.
