Polymorphic upward transformation and downward transformation 2016.12.8

As we all know, the override of a method is a polymorphic representation of the derived class and the base class, which can be transformed upward into a base class when instantiated, but the disadvantage is that the upward transformation can only implement the methods defined in the base class, but these methods are enriched in the export class.

In reality, we also need to extend the methods that are not in the base class in the export class, which is used when the instantiation is turned down to implement the extended method of the exported class.

The following examples illustrate:

Parent class Cycle Class:

 Package Cn.qdu.transport; class Cycle {    publicvoid  Ride () {        System.out.println ("Ride Cycle");    }          Public String wheels (string name,int  i) {        System.out.println (name+ "This means of transport has" +i+ "Wheels")        ; return name;}            }

Subclass Unicycle Class: Not only overrides the parent class ride () method, but also expands the new functionality, adds a new method balance ()

 Package Cn.qdu.transport; class extends Cycle {
@Override    publicvoid  Ride () {        System.out.println ("Ride unicycle.") );    }          Public void balance () {        System.out.println ("unicycle balance");}    }

Main function:

 Package Cn.qdu.transport;  Public class Test {    publicstaticvoid  main (string[] args) {        Cycle unicycle= New unicycle ();//Upward Transformation                cycle.ride ();        Cycle.wheels ("cycle", 2);                        Unicycle.ride ();        Unicycle.wheels ("Unicycle", 1);        ((Unicycle) unicycle). balance ();//Downward Transformation

Operation Result:

Ride Cyclecycle This kind of vehicle has 2 wheels ride unicycle.unicycle This means of transport has 1 wheels unicycle balance

Polymorphic upward transformation and downward transformation 2016.12.8