Hows does java allow a name like Map.Entry? I thought a dot is not allowed

Question

How is the dot allowed in this interface name, I cannot create another class/interface name with a dot in the name.

Answer 1

It's because Entry is a nested interface within the Map interface. You can create something similar if you want:

class MyClass {
  static class Nested { }
  public static void main(String[] args) {
    MyClass.Nested n = new MyClass.Nested();
  }
}

Or to answer your question more directly:

class MyClass {
  static class MyEntry implements Map.Entry { }
  public static void main(String[] args) {
    Map.Entry n = new MyEntry();
  }
  interface Map {
    interface Entry {}
  }
}

Answer 2

As Kevin Esche commented, when creating an inner class, it's fully qualified name would become foo.bar.Outer.Inner.

Answer 3

The Entry interface is declared in the Map interface. It's an inner interface. So in order to use it, we have to make a reference to Map class, hence the Map.Entry.