What is the Template Method Pattern?

• Defines the skeleton of an algorithm in a method
• Defers some steps to a subclass
• Lets subclasses change some steps in the algorithm without changing the structure
• The Template Method contains an ordered series of primitive operations -- by (re)defining the primitive operations, subclasses change the algorithm

What Are Hooks?

• A Hook is a method defined in the base class with a default or empty operation
• Because it's not abstract, subclasses can ignore it
• Because it's there, subclasses can re-define it without changing the structure of the template
• If the hook returns a boolean for a conditional, it allows subclasses to change the flow of the algorithm

Abstract Vs Hooks

• Abstract Methods are requirements
• Hooks are optional

What Is the 'Hollywood Principle'?

• Don't call us, we'll call you.
• High-level components call low-level ones, not the other way around

Strategy Vs Template

• Strategy composes other objects chosen at runtime
• Template uses sub-classes
• Template provides better code re-use and strictly defines the algorithm
• Strategy provides better decoupling but the algorithm is provided by the composed objects