EffectiveJava notes

EffectiveJava notes

item 17: design and document for inheritance or else prohibit it
	
	DESIGN:
		ELIMINATE seft-use of overridable methods entirely (with private helper methods) or DOCUMENT its
			constructor must not invoke overridable methods
		judiciously expose protected method that provide hooks to internal working 

	TEST: write sub classes
	
	PROHIBIT SUBCLASSING (preferably for class implmenting interfaces): 
		+ final class
		+ private or package-private constructor + factory methods
		=> use Wrapper Pattern for extending class functionalities

item 18: Prefer interfaces to abstract class
	
	WHY interfaces or abstract class: a type that permit multiple implementations

	WHY interfaces: 
		Non-hierarchical type frameworks
		Interface enables safe, powerful functionality enhancements (wrapper class idiom)

	DESIGN Interface with utmost care as it's hard to change

	EXCEPTION: when evolution is deemed more important than flexibility and power
	
	Conbine virtue of interfaces + abstract class => abstract skeletal implementation

item 19: use interfaces only to define types
	constant interface -> replaced by 
		enum type
		noninstantiable utility class

item 20: use function objects to represent strategies:
	
	example: Comparator<T>

	function objects: object with only one method, (use anonymous class syntax)

	STRATEGY PATTERN:
		declare an Interface to represent the strategy
		a class implenments this interface for each concreate strategy

		if concrete strategy 
			used once: 	-> anonymous class
			used often: -> export to static final field

item 21: Favor static member classes over nonstatics
	Nested class:
		static member class 
			commom use: public  :helpler class
						private : represent component of the class (Map implentation with Entry component)
		nonstatic member classes
			common use: Adapter (like Iterator<T>)
		anonymous class
		local class