gistfile1.scala

// Some plain classes with subclasses
class Foo
class SubFoo extends Foo
class SubSubFoo extends SubFoo
class SubSubSubFoo extends SubSubFoo

// A generic class
class Bar[T <: Foo](val foo: T) {

}

object Main{
  //def extractFoo(bar: Bar[_]): Foo = bar.foo  // This does not compile
  def extractFoo2(bar: Bar[_ <: Foo]): Foo = bar.foo // But this does.
  // def extractAny(bar: Bar[_ <: Any]): Foo = bar.foo // This also does not compile.
}

gistfile2.java

package com.v6ak.experiments;


// Some plain classes with subclasses
class Foo{}
class SubFoo extends Foo{}
class SubSubFoo extends SubFoo{}
class SubSubSubFoo extends SubSubFoo{}

// A generic class
class Bar<T extends Foo>{

    private final T foo;

    public Bar(T foo) {
        this.foo = foo;
    }

    public T getFoo() {
        return foo;
    }

}


public class Main {

    // All of these methods work in Java:
    public static Foo extractFoo(Bar<?> bar) {
        return bar.getFoo();
    }

    public static Foo extractFoo2(Bar<? extends Foo> bar){
        return bar.getFoo();
    }

    public static Foo extractAny(Bar<? extends Object> bar){
        return bar.getFoo();
    }

}