why subclass reference can't hold superclass object in java

Question

class One{

}
class Two extends One{

}
class Main{

      public static void main(String[]  args){
       Two t = new One(); // invalid 

}`
}

I a

Answer 1

The type of TWO cannot be an instance of ONE because there are members and methods that TWO has which ONE doesn't have. However, The type of ONE can reference TWO because TWO has everything that ONE has.

For example, if ONE can WALK and TWO can also RUN, then if you have an object from the type ONE then is needs to be able to WALK. So if ONE references TWO that works because TWO can walk.

But when you have an object of type TWO then it needs to be able to RUN so you cannot reference it to ONE which cannot RUN.