Conversion of word classes and super classes

For example, there are two classes. Father is the parent class, and son class inherits from father.

Father F1 = new son (); // This is called upcasting (upward transformation)

// Now F1 references a son object

Son S1 = (son) F1; // This is called downcasting (downward transformation)

// At present, F1 still points to the son object

2nd examples:

Father F2 = new father ();

Son S2 = (son) F2; // error, subclass reference cannot point to parent class Object

 

In this case, a super-class instance cannot be converted into a subclass.

Therefore, when writing to the Inheritance Organization, you must use a word class instance to assign a reference to the super class.

Package package = new umppackage ()