Hanshunping-Step Learning Java 12th polymorphism

12.1 polymorphic-Four characteristics12.1.1Concept

The so-called polymorphic, refers to a reference (type) in different situations in a variety of states.

It can be understood that polymorphism refers to a method that is implemented in a different subclass by pointing to a pointer to the parent class.

12.1.2 Precautions

In explaining polymorphism, we noticed a phenomenon - type conversion.

1. Java allows a reference variable of the parent class to refer to an instance of its subclass (object)

Animal animal=new Cat ();

2, there are some details about type conversion requirements, such as whether the subclass can be converted to a parent class, what requirements and so on ...

Polymorphic Code Demo:

1 /**Date: 2016-03-042 * Function: Multi-state demo3  */4  Public classPractice5 {6      Public Static voidMain (String []args)7     {8Master master=NewMaster ();9Master.feed (NewCat (),NewFish ());//calling subclassesTen     } One } A  - classMaster//class owner - { the      Public voidFeed (Animal Animal, food food)//Polymorphic method that can invoke subclasses with the parent class, -     //Here the code can be added to the sub-class when it is not moving, very convenient -     { - animal.getname (); + food.eat (); -     } + } A  at classAnimal//The parent class animal - { - String name; -      Public voidGetName () -     { -System.out.println ("Don't know what the animal is!" "); in     } - } to  + classCatextendsAnimal//Animals of the sub-category cat - { the      Public voidGetName () *     { $System.out.println ("This is a cat!") ");Panax Notoginseng     } - } the  + classDogextendsAnimal//the animal's sub-type dog A { the      Public voidGetName () +     { -System.out.println ("This is a dog!") "); $     } $ } -  - classFood//Food of the parent class the { - String name;Wuyi      Public voidEat () the     { -System.out.println ("Don't know what food!" "); Wu     } - } About  $ classFishextendsFood//Food of the sub-type fish - { -      Public voidEat () -     { ASystem.out.println ("Cats love to eat fish!") "); +     } the } -  $ classBoneextendsFood//Child bones of food the { the      Public voidEat () the     { theSystem.out.println ("Dog loves bones!") "); -     } in}

Operation Result:

1 this is a cat!  2 cats love to eat fish!

Hanshunping-Step Learning Java 12th polymorphism