scope of private constructor in Nested Class

if the member or constructor is declared private, then access is permitted if and only if it occurs within the body of the top level class (§7.6) that encloses the declaration of the member or constructor.

http://docs.oracle.com/javase/specs/jls/se7/html/jls-6.html#jls-6.6.1

Because anything declared inside a class can access its private members, including inner classes. However, if you run PMD on your class, you'll find it suggests you change the visibility of the constructor to not-private.

Because nested classes can see each others members. This has nothing to do with the static declarations. See the following example of your code with just nested inner classes (not static).

public class PrivateBaseConstructor {
    public class BaseClass {
        private BaseClass() {}
    }

    public class DerivedClass extends BaseClass {
        public DerivedClass() {
            super(); // 1*
        }
    }

    public static void main(String[] args)
    {
       new PrivateBaseConstructor(). new DerivedClass();
    }
}

Read more about nested classes here: http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html