com.google.auto.value.extension.memoized

Annotation Type Memoized

@Documented
 @Retention(value=CLASS)
 @Target(value=METHOD)
public @interface Memoized

Annotates methods in @AutoValue classes for which the generated subclass will memoize the returned value.

Methods annotated with @Memoized cannot:

• be abstract (except for Annotation.hashCode() and Annotation.toString()), private, final, or static
• return void
• have any parameters

If you want to memoize Annotation.hashCode() or Annotation.toString(), you can redeclare them, keeping them abstract, and annotate them with @Memoize.

If a @Memoized method is annotated with an annotation whose simple name is Nullable, then null values will also be memoized. Otherwise, if the method returns null, the overriding method will throw a NullPointerException.

The overriding method uses double-checked locking to ensure that the annotated method is called at most once.

Example

    @AutoValue
   abstract class Value {
     abstract String stringProperty();

      @Memoized
     String derivedProperty() {
       return someCalculationOn(stringProperty());
     }
   }

    @Generated
   class AutoValue_Value {
     // …

     private volatile String derivedProperty;

      Override
     String derivedProperty() {
       if (derivedProperty == null) {
         synchronized (this) {
           if (derivedProperty == null) {
             derivedProperty = super.derivedProperty();
           }
         }
       }
       return derivedProperty;
     }
   }