SingletonCustomizer (FreeMarker 2.3.23 API)
Date: 2015-07-05

freemarker.ext.beans

## Interface SingletonCustomizer

-     public interface SingletonCustomizer

  Marker interface useful when used together with `MethodAppearanceFineTuner` and such customizer objects, to indicate that it doesn't contain reference to the `ObjectWrapper` (so beware with non-static inner classes) and can be and should be used in call introspection cache keys. This also implies that you won't create many instances of the class, rather just reuse the same (or same few) instances over and over. Furthermore, the instances must be thread-safe. The typical pattern in which this instance should be used is like this:

      static class MyMethodAppearanceFineTuner implements MethodAppearanceFineTuner, SingletonCustomizer {

          // This is the singleton:
          static final MyMethodAppearanceFineTuner INSTANCE = new MyMethodAppearanceFineTuner();

          // Private, so it can't be constructed from outside this class.
          private MyMethodAppearanceFineTuner() { }

          @Override
          public void fineTuneMethodAppearance(...) {
             // Do something here, only using the parameters and maybe some other singletons.
             ...
          }

       }

  Since:
    2.3.21