未知/通配符（？）方法调用中的通用类型

Question

I have the following two interfaces:

public interface ParsedFile<K, V extends FileEntry>{...}

And

public interface MetricsProduces<K, V extends FileEntry>{
    Metrics generateMetrics(ParsedFile<K, V> parsedFile);
}

I have the following generic code the should be able to handle any FileEntry types:

Option<FileDefinition> option = fileContainer.matchFile(file);
if (option.isSome){
  FileDefinition fileDef = option.some();
  ParsedFileFactory<?> factory = filterDefinition.getFactory();
  ParsedFile<?, ?> parsedFile = factory.parseFile(file);
  MetricsProducer<?, ?> metricsProducer = fileDefinition.getMetricsProducer();
  Metrics metrics = metricsProducer.generateMetrics(parsedFile);
}

This block of code is designed to be able to parse any type of file given the appropriate FileDefinition. However I am getting the following compile-time error:

The method generateMetrics(ParsedFile<capture#5-of ?, capture#6-of ? extends FileEntry>) 
in the type MetricsProducer<capture#5-of ?, cature#6-of ? extends FileEntry> 
is not applicable for the arguments 
(ParsedFile<capture#7 of ?, capture#8-of ? extends FileEntry>)

Is there a way to let the compiler know that the "?" type of ParsedFile is the same as the "?" type of MetricsProducer? Is there another option for doing this?

Edit:

I have fixed (as noted this causes a cast warning) the code as follows but was wondering if there is a better option:

public interface MetricsProduces<K, V extends FileEntry>{
    Metrics generateMetrics(ParsedFile<?, ? extends FileEntry> parsedFile);
}

public class TasksMetricsProduces<String, TaskFileEntry> implements MetricsProduces<...>{

    public Metrics generateMetrics(ParsedFile<?, ? extends FileEntry> parsedFile){
         ParsedFile<String, TaskFileEntry> parsedFile2 = (ParsedFile<String, TaskFileEntry>)parsedFile;
    }
}

Edit 2: per comments / suggestions

So I found that if I lock down the types earlier I can do the following:

public interface FileDefinition<K, V extends FileEntry, T extends ParsedFile<K, V>>{...


public void myMethod(){
     for (FileDefinition<?, ?, ?> def : defs){
         process(def);
     }
}

private <K, V extends FileEntry, T extends ParsedFile<K, V>> process(FileDefinition<K, V, T> def){
     Factory<T> factory = def.getFactory();
     MetricsProducer<K, V> producer = def.getMetricsProducer();
     ParsedFile<K, V> parsedFile = factory.parseFile();
     Metrics metrics = producer.generateMetrics(parsedFile);
}

Thanks for the suggestions.

Answer 1

Regarding your comments above and the following code I think there is no easy soltion:

ParsedFile<?, ?> parsedFile = factory.parseFile(file);
MetricsProducer<?, ?> metricsProducer = fileDefinition.getMetricsProducer();

as long as factory.parseFile(...) or ParsedFileFactory itself isn't paremeterized properly as well as fileDefinition.getMetricsProducer() or FileDefinition you can never be sure that the objects created by the two of these methods are matching.

Answer 2

Maybe you can bind the ? to the same type parameter in way similar to this:

<K, V extends FileEntry> void myMethod(){
    Option<FileDefinition> option = fileContainer.matchFile(file);
    if (option.isSome){
        FileDefinition fileDef = option.some();
        ParsedFileFactory<?> factory = filterDefinition.getFactory();
        ParsedFile<K, V> parsedFile = factory.parseFile(file);
        MetricsProducer<K, V> metricsProducer = fileDefinition.getMetricsProducer();
        Metrics metrics = metricsProducer.generateMetrics(parsedFile);
    }
}

Answer 3

Found that it worked if I locked down the generic types earlier to show the compiler that the types for the objects are the same.

public interface FileDefinition<K, V extends FileEntry, T extends ParsedFile<K, V>>{...


public void myMethod(){
     for (FileDefinition<?, ?, ?> def : defs){
         process(def);
     }
}

private <K, V extends FileEntry, T extends ParsedFile<K, V>> process(FileDefinition<K, V, T> def){
     Factory<T> factory = def.getFactory();
     MetricsProducer<K, V> producer = def.getMetricsProducer();
     ParsedFile<K, V> parsedFile = factory.parseFile();
     Metrics metrics = producer.generateMetrics(parsedFile);
}

Answer 4

MetricsProducer<?, ? extends FileEntry> metricsProducer = fileDefinition.getMetricsProducer();