Java APIs

I have a method with a Map<String, Object> parameter:

public void do1(Map<String,Object> map) {
    ...
}

I can call this method with a Map<String, Object> parameter value but get a compile error when I try to call it with a Map<String, String> parameter value:

The method do1(Map<String,Object>) in the type Translator is not applicable for the arguments (Map<String,String>)

But why? String is a subclass of object so it should also work?