Transformation and down-conversion in Java (object polymorphism)

/* on transition and down transformation (object polymorphism)
* On transition: is a subclass object referenced by the parent class, format: Parent p=new son
* That is to say, the prerequisite for a transition must be two classes with an inheritance relationship.
* When invoking a method, the upper transformation object can only invoke methods in the parent class, and if the method of calling the subclass will error
* Down Transformation: is the parent class is cast down to the child class object
* If the parent class object must be an object that has been transformed.
*
* Code Example: */

1 Abstract classparent{2     Abstract voidgrow ();3 }4 classSonextendsparent{5     voidgrow () {6System.out.println ("I grew up better than my father."));7     }8     voidDance () {9System.out.println ("I Can Play");Ten     } One } A  Public classTest { -      Public Static voidMain (string[] args) { -         //on the transformation, use the parent class to refer to the object of the child class theParent p=NewSon (); -         //calling methods in the parent class - P.grow (); -         //p.dance (); There will be an error because there is no dance () method in the parent class +          -         //Make a forced transition to an object that has been transformed +Son s=(Son) p; A         //calling a method in a subclass at s.dance (); -     } -}

/*
* In our writing program, we seldom write the code to death, for example, there will be daughter class
* and then in the wrapper function to invoke the object, perhaps the method of subclasses, here we explain this aspect of knowledge.

1 Abstract classparent{2     Abstract voidgrow ();3 }4 classSonextendsparent{5     voidgrow () {6System.out.println ("I grew up better than my father: Son");7     }8     voidPlay () {9System.out.println ("I Can Play");Ten     } One } A classDaughterextendsparent{ -     voidgrow () { -System.out.println ("I grew up better than my father: Daughter"); the     } -     voidDance () { -System.out.println ("I Can Dance"); -     } + } -  Public classTest { +      Public Static voidMain (string[] args) { AParent p=NewSon (); at Show (p); -Parent p2=Newdaughter (); - Show (p2); -     } -      Public Static voidShow (Parent p) { -             //now output the methods in the parent class in P.grow (); -             //type judgment on the objects that have been transformed and then make the corresponding forced transformation to             if(pinstanceofSon) { +                 //determine which class is on the top of the transformation object and then make the next transformation -Son s=(Son) p; the                 //calling a method in a subclass * S.play (); $}Else if(pinstanceofdaughter) {Panax NotoginsengDaughter D=(daughter) p; - d.dance (); the             } +              A     } the}

Transformation and down-conversion in Java (object polymorphism)