Object-Oriented Design

• Avoid global variables.
• Avoid long parameter lists.
• Limit dependencies of an object (entities an object depends on).
• Limit an object's dependents (entities that depend on an object).
• Prefer composition over inheritance.
• Prefer small methods. Between one and five lines is best.
• Prefer small classes with a single, well-defined responsibility. When a class exceeds 100 lines, it may be doing too many things.
• Tell, don't ask.