alessandrognoatto / mafinlib Goto Github PK

Where is WesternImpl?

I am not sure if this class is truly useful - see my PM - but as a general comment you could use a ConcurrentHashMap here:

Instead of using a Singleton that maintains a Map to other Singletons you may consider a static initialiser:
https://stackoverflow.com/questions/3635396/pattern-for-lazy-thread-safe-singleton-instantiation-in-java

At

the double checked locking idiom is used. This is broken in this form (since the member is non volatility). To fix it the member (singleton) should be volatility (also note that your singleton is not immutable)!

Background Information on Double Checked Locking

Double Checked Locking was broken in Java 1.4 and fixed in 1.5 (around 2005) using the keyword volatility.
See
https://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
and
http://www.angelikalanger.com/Articles/EffectiveJava/41.JMM-DoubleCheck/41.JMM-DoubleCheck.html
Note that Double Checked locking is also broken in C++ and this is fixed in C++ 11 (around 2011), see
http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/

Improvements

For lazy init I would recommend to use a standard LazyInitializer:
https://commons.apache.org/proper/commons-lang/javadocs/api-3.1/org/apache/commons/lang3/concurrent/LazyInitializer.html
implementing a ConcurrentInitializer:
http://commons.apache.org/proper/commons-lang/javadocs/api-3.1/org/apache/commons/lang3/concurrent/ConcurrentInitializer.html

But for Singlestons lazy initialisation is trivial because you can use a static initializer - note that classed are not loaded until they are needed (Java does Lazy w.r.t. class loading) and a static initalizer is executed upon class loading - and thread safe by spec:
https://stackoverflow.com/questions/3635396/pattern-for-lazy-thread-safe-singleton-instantiation-in-java