How to implement something like Terracota?

How Terracotta knows that object is changed inside one JVM to propagate this change to another JVM? I.e. how can I code similar behavior?

I want to b开发者_JAVA百科e able to watch changes in instances of some classes, without changing them at all.

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It uses instrumentation. It's explained (in high level) in the terracotta wiki

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Shouldn't a observer pattern help. If you implement your class as observable and have an oberver , the observer will be notified when ever the observable class goes through some change.