Java通用抽象类返回类型不匹配

Question

I have an abstract class in java:

private abstract class Importable<T> {

    // ...

    public abstract List<T> validateData(List<Path> paths);

    public abstract void importData(List<T> data);

    // ...

}


private static class MyImportable  extends Importable<String>{

    public List<String> validateData(List<Path> paths){
        return // valid ArrayList<String>;
    }

    public void importData(List<String> data){
        // do stuff with data
    }    

}

Now, if I do this:

public Importable importable;
// ...
importable = new MyImportable(); // MyImportable extends Importable<String>

calling this works:

importData(validateData(myPaths));

But I don't like the raw Importable , so I added <?>

public Importable<?> importable; 

doing so throws error:

The method importData(List<capture#5-of ?>) in the type ImportController.Importable<capture#5-of ?> is not applicable for the arguments (List<capture#6-of ?>)

while executing importData(validateData(myPaths));

and eclipse suggests me to cast to List<?> , which did nothing to solve the problem

Is there something I'm missing?

EDIT: sorry if I wasn't clear, here is the actual usage

I will have many class that extends Importable with different types:

Importable importable;

switch(condition){
case 1:
    importable= // Importable<MyType1>
break;
case 2:
    importable= // Importable<MyType2>
// ....

}

importData(validateData(myPaths)); 

EDIT2:

I intentionally separate importData and validateData because some other class might want to validateData only

If matters: I'm using eclipse 4.3 w/ Java 8 on Windows 7 x64

Answer 1

Replace the generic argument ? with String

EDIT (taking the edited question into account):

I think that the following would be a better design:

switch(condition){
case 1:
    validateAndImport(someImportable, paths); //Importable<MyType1>
break;
case 2:
    validateAndImport(someOtherImportable, paths); //Importable<MyType1>
}

...

<T> void validateAndImport(Importable<T> importable, List<Path> paths) {
   importable.importData(importable.validateData(myPaths))
}

Answer 2

This will solve your problem

public Importable<String> importable;
// ...
importable = new MyImportable(); // MyImportable extends Importable<String>

as you know MyImportable extends Importable<String>

---

--EDIT--

as per you updated question, please try this one

abstract class Importable<T> {

    public abstract List<T> validateData(List<Path> paths);

    public abstract void importData(List<? extends Object> list);

}

and use

public Importable<? extends Object> importable;