WHAT DOES THISJAV MEAN?

The . is just the regular member entry, it really works in the exact same way as in all other conditions, absolutely nothing Exclusive is happening in case of this.サブクラスはスーパークラスのメンバ変数やメソッドを継承しています。サブクラスにスーパークラスと同じ名前の変数やメソッドがある