Java Learning--object-oriented feature three: polymorphism

* Object-oriented feature three: Polymorphism
* 1. What does polymorphism mean? Polymorphism, which can be understood as a variety of forms of a thing's phenotype.
* 1) method overloads and overrides 2) the polymorphism of the sub-class object
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* 2. Subclass Object Polymorphism Use premise: ① to have class inheritance ② to have subclasses override the parent class method
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* 3. The program runs into a compilation state and a running state.
* For polymorphism, at compile time, "look left", this reference variable is interpreted as the type of the parent class
* Runtime, "Look right", focus on the entity of the real object: The object of the subclass. Then the method of execution is the subclass rewrite.
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* 4. The polymorphism of the subclass object is not used for attributes.

1  Public classTestperson {2      Public Static voidMain (string[] args) {3Person p =NewPerson ();4 p.eat ();5 P.walk ();6 7Man m =NewMan ();8 m.eat ();9 M.Walk ();Ten System.out.println (); One  A         //the polymorphism of a subclass object: a reference to a parent class to a subclass object -person P1 =NewMan ();//Upward Transformation -         //virtual method invocation: Refers to the object entity of the subclass through a reference to the parent class, and when the method is called, the child class is actually executing the method of overriding the parent class the p1.eat (); - P1.walk (); -SYSTEM.OUT.PRINTLN ("$" + p1.id);//1001 -  + //p1.smoking = null; -         //p1.entertainment (); +  Aperson P2 =NewWoman (); at p2.eat (); - P2.walk (); -         //p2.shopping (); -Woman w = (Woman) P2;//transition downward, using strong-to-go: () - w.shopping (); -  in         //java.lang.ClassCastException -         //Woman w1 = (Woman) p1; to         //w1.shopping (); +  -         //Woman w2 = (Woman) new Man (); the         //instanceof: *         //format: Object A instanceof Class A: Determines whether object A is an instance of Class A. Yes, returns true; otherwise returns false $         //If A is an instance of Class A, then a must also be an instance of the parent class of Class A. Panax Notoginseng         if(P1instanceofWoman) { -System.out.println ("hello!"); theWoman W1 =(Woman) p1; + w1.shopping (); A         } the  +         if(P1instanceofMans) { -Man M1 =(man) p1; $ m1.entertainment (); $         } -  -         if(P1instanceofPerson ) { theSYSTEM.OUT.PRINTLN ("Hello! "); -         }Wuyi  the     } -  Wu      Public voidShow (person p) {//Person p = new Mans (); -  About     } $  -  -  - classPerson { A     PrivateString name; +     Private intAge ; the     intID = 1001; -      PublicPerson () { $         Super(); the     } the      PublicPerson (String name,intAge ) { the         Super(); the          This. Name =name; -          This. Age =Age ; in     } the      PublicString GetName () { the         returnname; About     } the      Public voidsetName (String name) { the          This. Name =name; the     } +      Public intGetage () { -         returnAge ; the     }Bayi      Public voidSetage (intAge ) { the          This. Age =Age ; the     } -     -      Public voidWalk () { theSystem.out.println ("People walking"); the     } the      Public voideat () { theSYSTEM.OUT.PRINTLN ("People eat"); -     } the  the } the 94  the  the  the classMansextendsperson{98      Booleansmoking; About      intID = 1002; -      PublicMan () {101         Super();102     }103    104      PublicMans (Booleansmoking) { the         Super();106          This. Smoking =smoking;107     }108 109      Public Booleanissmoking () { the         returnsmoking;111     } the 113      Public voidSetsmoking (Booleansmoking) { the          This. Smoking =smoking; the     } the    117      Public voidWalk () {118System.out.println ("Men walking in a straight walk");119     } -      Public voideat () {121System.out.println ("Men should eat more meat!") ");122     }123    124      Public voidEntertainment () { theSystem.out.println ("Men's Treat");126     }127 } - 129  the classWomanextendsperson{131     Private Booleanisbeauty; the 133      Public Booleanisbeauty () {134         returnisbeauty;135     }136 137      Public voidSetbeauty (Booleanisbeauty) {138          This. Isbeauty =isbeauty;139     } $ 141      PublicWoman () {142         Super();143     }144 145      PublicWoman (Booleanisbeauty) {146         Super();147          This. Isbeauty =isbeauty;148     }149      Public voidWalk () { MaxSystem.out.println ("A woman walking with a slim ... ");151     } the    153      Public voideat () {154SYSTEM.OUT.PRINTLN ("Women should eat less, lose weight");155     }156      Public voidShopping () {157System.out.println ("Women love Shopping");158     }159     the}

Java Learning--object-oriented feature three: polymorphism