class concept

class a
{
public void aFn()
{
System.out.println("Im in A");
}
}
class b
{
public void bFn()
{
System.out.println("I'm in B");
}
public static void main(String args[])
{
class a= new a();
a.aFn();
class b= new b();
b.bFn();
}
}

the name of the file saved is b.java

The output is
Im in A
Im in B

My question is that how can we access other class as the default access specifier is package. we haven't imported the package.

Please clear me through the concept of accessing a class .