[FIXED] Pattern for Java generics for "internal" type

Issue

I have a class. Its public interface (excluding the constructor) is not generic, but its internal logic is. A simplified example of this is:

class Summarizer<T> {
  private final ComplicatedProducer<T> producer;
  private final Processor<T> processor;

  StreamSummarizer(ComplicatedProducer<T> producer, Processor<T> processor) {
     ...
  }

  public int summarizeAll() {
    int sum = 0
    // some business logic goes here
    for (...) {
      sum += processor.process(producer.next());
    }
    return sum;
  }

  public int summarizeSomePortion(Parameters p) {
    // some other business logic goes here
    ...
  }
}

Note that (after construction), the user of Summarizer has no interest in T's type. In my case, the type isn't known at compile time (we use reflection to construct ComplicatedProducer and Processor), and I'd rather not have to have a factory function that returns Summarizer<?>. Is there any clean way to make Summarizer non-generic without resorting to the use of raw types?

Solution

You can always have a single-level wrapper:

class SummarizerImpl<T> {
    private final ComplicatedProducer<T> producer;
    private final Processor<T> processor;

    SummarizerImpl(ComplicatedProducer<T> producer, Processor<T> processor) {
      ...
    }
}

class Summarizer {
   private final SummarizerImpl<?> impl;
   private Summarizer(SummarizerImpl<?> impl) { ... }
   public static <T> Summarizer create(
       ComplicatedProducer<T> producer, Processor<T> processor) {
     return new Summarizer(new SummarizerImpl<T>(producer, processor));
   }
}

Answered By - Louis Wasserman