General Java Type Resolution

Question

I started working with Java recently and am still confused when working with generic types. The following is a simplified scenario in which some problems arise.

I have a class that contains a map using the class type as a key and a collection of objects of this class:

public class GenericListInside {
    private Map<Class<?>, List<?>> mapping = new HashMap<>();

    public <T> void addListing(Class<T> clazz, List<T> object) {
        mapping.put(clazz, object);
    }
}

I can call addListing without problems:

GenericListInside gli = new GenericListInside();
List<Foo> list = new ArrayList<>(); 
//add something to list
gli.addListing(Foo.class, list); 

Now I decided to create a class to provide a fluid interface. Sort of:

with(Foo.class).use(list);

Then I came with:

public class FluidInserter<T> {
    Class<T> clazz;
    GenericListInside gli = new GenericListInside();

    public FluidInserter with (Class<T> clazz) {
        this.clazz = clazz;
        return this;
    }

    public <T> void use(List<T> list) {
        gli.addListing(clazz, list);
    }
}

But when I try to compile, I get:

: (18, 12) java: addListing util.GenericListInside .
  : java.lang.Class, java.util.List
  : java.lang.Class, java.util.List
  : (s)
    inferred: T
     (s): T, T

... - , ?

Answer 1

, clazz, .

<T> , List<T> :

public void use(List<T> list) {
    gli.addListing(clazz, list);
}

: FluidInserter with. :

public FluidInserter<T> with (Class<T> clazz)

Answer 2

use(List<T> list):

public <T> void use(List<T> list) {
    gli.addListing(clazz, list);
}

- T , .

:

public void use(List<T> list) {
    gli.addListing(clazz, list);
}

, T .

Answer 3

:

public <T> void use(List<T> list) {
    gli.addListing(clazz, list);
}

<T> , .

:

public void use(List<? extends T> list) {
    // same logic here
}

, , , GenericListInside. mapping , .

Edit

You can add a common character to GenericListInsideas follows:

public class GenericListInside<T> {

    private final Map<Class<T>, List<T> mapping = new HashMap<>();

    public void addListing(Class<T> clazz, List<T> list) {
        mapping.put(clazz, list);
    }
}