Added the latest implementation way of singleton in Java.
Added Example code for Minimize mutability in Effective Java.
Added Example code for perfering composite to inherence.
Added Public class with exposed immutable fields - questionable for
immutable implementation in Effective Java.
Added Implementation of preference to composite to inherence.
Refined the demo for InstrumentedSet by setting the d2(Date) with method
which is not depricated.
Added demo for prefering interface to abstract class.
Merge branch 'master' of https://github.com:443/haokaibo/AlgorithmHelper.git