Template Method Pattern 模板方法模式

Template Method Pattern: defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

准备一个抽象类，将部分逻辑以具体方法以及具体构造子的形式实现，然后声明一些抽象方法来迫使子类实现剩余的逻辑。不同的子类可以以不同的方式实现这些抽象方法，从而对剩余的逻辑有不同的实现。这就是模版方法模式的用意。

This pattern is all about creating a template for an algorithm. It;s a method that defines an algorithm as a set of steps. Some steps are concrete, some are abstract.

public abstract class Template {
	protected final void TemplateMethod() {
		primitiveMethod();
		concreteMethod();
		hook();
	}
	protected abstract void primitiveMethod1();
	protected final void concreteMethod() {
		//do something
	}
	protected hook() {}
}

A hook is a method that is declared in the abstract class, but only given an empty or default implementation. So subclass can either use the default method or override the hook method.

Design Principle:

Hollywood Principle: Don't call us, we'll call you.

Allow low-level components to hook themselves into a system, but the high-level components determine when they are needed, and how.