Head First Design Patterns - Template Method Pattern

The Template Method Pattern defines the skeleton of algorithm in a method, define some steps to 

subclasses. Template Method lets subclass redefine certain steps of an algorithm without changing

the algorithm's structrue.

Class diagram:

abstract class AbstractClass{

　　final void templateMethod(){

　　　　primitiveOperation1();

　　　　primitiveOperation2();

　　　　concreteOpration();

　　}

　　abstract void primitiveOperation1();

　　abstract void primitiveOperation2();

　　void concreteOperation(){

　　　　// implementation here

　　}

　　void hook(){}

}

A hook is a method that is declared in the abstract class, but only given an empty or default implementation,use hooks

when that part of the algorithm is optional, with hooks, a subclass may choose to implement that hook, but it doesn't have to.

The Hollywood Priciple:

• Don't call us, we'll call you

the Hollywood principle gives us a way to prevent "dependency rot". Dependency rot happens when you have high-level 

components depending on low-level components.

The Strategy and Template Method Patterns both encapsulate algorithms, one by inheritance and one by composition.