In an interface, I first declare a generic that extends an interface, then a generic that extends the first generic along with another interface

Question

For example,

public interface Foo<T extends Blackness, S extends T & Whiteness> { }

Error: Type parameter cannot be followed by other bounds

Answer 1

T extends Blackness and S extends T so S inherently extends Blackness. The only other contingency is that S must also extends Whiteness. Because of this restriction, S must be an extension of T but also implement the functionality of Whiteness. Because of this, you will likely have to provide the type T. It's not possible for S to have multiple bounded types, which is why a sub-interface is required that implements both. What you're trying to do doesn't make logical sense. Refer to this.

    public interface Foo<T extends Blackness, S extends BlackAndWhiteness<T>> {

    }

    public interface BlackAndWhiteness<T extends Blackness> extends Whiteness, Blackness {
        
    }

    interface Blackness {

    }

    interface Whiteness {

    }