How to correctly specify the type of the callback argument without casting?

Question

Java

Let's say there is a callback

private void callback (Map<String, Color> data) {
       Color color = data.get("color");
}

which is passed as an argument to the method
new RenderThreadsController<>(this::callback);
In the method, this callback argument is of type interface

@FunctionalInterface
public interface Callback <T> {
    void callback (Map<String, T> data);
}

And called accordingly

Map<String, T> data = new HashMap<>();
        data.put(
            "color",
            (T) new Color(
                random.nextInt(255),
                random.nextInt(255),
                random.nextInt(255)
            )
        );
this.callback.callback(data);

Accordingly, the question is - is it possible to somehow do this without casting Color to T?

(T) new Color(
                random.nextInt(255),
                random.nextInt(255),
                random.nextInt(255)
            )

Answer 1

Map<String, T> data = new HashMap<>();
        data.put(
            "color",
            (T) new Color(
                random.nextInt(255),
                random.nextInt(255),
                random.nextInt(255)
            )
        );
this.callback.callback(data);

At this point, the type in the map is known, so there is no point in parametrizing the value type, it is better to explicitly specify the Color type, i.e. Map data = new HashMap<>();
If the map can contain values ​​of different types, then you can use the advice from Joshua Bloch - idlebrains.org/tutorials/java-tutorials/effective-...

Answer 2

in java there is such a thing as Wildcards
<? extends T>
<? super T>