Question

The following code compiles in JDK6. Fails in JDK7 with compilation error.

java: incompatible types
  required: com.jdk7.IExporter<O>
  found:    com.jdk7.IExporter<java.lang.Object>

Compiler is 1.7.0_10, from Oracle.

$ javac -version
javac 1.7.0_10

Code

package com.jdk7;

public class GenericIn7 {

    public <O> IExporter<O> getExporter(Class<O> objType) {
        final IExporter<O> localExporter = 
                determineExporter(getPersistentInterface(objType));
        return null;
    }

    private <O> IExporter<O> determineExporter(Class<O> persistentInterface) {
        return null;
    }

    protected <O, I extends O> Class<O> getPersistentInterface(Class<I> clazz) {

        return null;
    }
}

class IExporter<T> {
}

[For sake of completeness,
replacing generic with IExporter and other changes make it compile. ]

Answer 1

Looks like the type inference just isn’t working as you expect on this line:

final IExporter<O> localExporter = 
            determineExporter(getPersistentInterface(objType));

I think the problem is what O is being resolved to in getPersistentInterface(). It is being called as if you had called this.<Object, O>getPersistentInterface(...). If you are explicit:

final IExporter<O> localExporter = 
            determineExporter(this.<O, O>getPersistentInterface(objType));

it works fine.