Why does an inner class method hide all the enclosing class methods with the same name?

Considering the java code below:

class Enclosing {
    void method(){}
    void method(String str){}

    class Inner {
        void method(){}
    }   
}

I am reading a book which tells me that Inner.method() will hide both versions of Enclosing.method(), which means it is an error if I call method(aString) somewhere in class Inner.

Why is the language designed like that?

Update:
According to the answer given by @Debosmit Ray, it is related to shadowing. I have read the docs and understood what it is.

What still confusing me is why method shadowing is based on method name not method signature?