Friday, November 19, 2010

parameterized wrapper class with a superclass

(This looks like a low-level and widely usable implementation pattern. If it is, then we better learn to read it. However, I don’t see many java guys create generic classes.)

 

A wrapper class’s behavior is affected by 3 types of things

 

·         The “kernel” fields wrapped in the wrapper. In addition, there are often helper fields, too.

·         The parent class

·         The type param. Remember this class is parameterized.

 

This looks simple until you see it used in a complex system. You need to remember how these “influences” are set.

 

public class EntityCacheListenerAdapter<K, V extends Entity<K>, T extends EntityListener<K,V>>

extends AbstractCacheListenerAdapter<T, K, V> {

      public EntityCacheListenerAdapter(T target) {

            super(target); // populating this.target

      }

      @Override

      public void afterUpdate(EntryEvent<K, V> event) {

            super.getTarget() // inherited from parent

             .entityUpdated( // this method is from the kernel field

                    event.getOldValue(), event.getNewValue());

      }

 

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