Java Note 6__ abstract class/interface/polymorphic/instanceof keyword, parent design rule

/*** Abstract class: Many classes with the same characteristics and behavior can be abstracted as an abstract class * 1. Abstract classes can have no abstract methods, and classes with abstract methods must be abstract classes * 2. Abstract classes that are not abstract classes must implement abstract methods "can be NULL implementations" * 3. Abstract classes can have methods and properties * 4. Abstract classes cannot be instantiated * 5. Abstract classes cannot be declared as final * 6. Abstract classes can have a constructor method "does not represent an instantiated object"*/ Public classMain { Public Static voidMain (string[] args) {Goddess M1=Newgoddess (); M1.setname ("Dining");                M1.say (); Ugly m2=NewUgly (); M2.setname ("Fish");;    M2.say (); }  }Abstract classwoman{//woman as abstract class    PrivateString name;  PublicWoman () {System.out.println ("I am the constructor of an abstract class. "); }     Public voidsetName (String name) { This. Name =name; }     PublicString GetName () {returnname; }     Public Abstract voidSay ();//abstract method (declaration only, not implemented)}classGoddessextendswoman{//implementing an abstract method of the parent class     Public voidsay () {System.out.println ("I am the goddess, my name is:" +getName ()); }}classUglyextendswoman{ Public voidsay () {System.out.println ("I am an ugly girl, my name is:" +getName ()); }}

/*** Interface: A set of behavior specifications, definitions, not implemented * Interface Definition Format: * Interface interface Name {* Global constant; * abstract method; *} * 1. A class can implement multiple interfaces * 2. Abstract class implementation interface can not implement method * 3 The access rights for all methods in the interface must be public * 4. The properties defined in the interface are constants*///define an interfaceInterfacehit{ Public Static FinalString NAME = "D";//properties defined in an interface are constants public static final can be omitted     Public voidCry ();//Abstract method Public abstract (can be omitted)}Interfaceieat{ Public voideat ();}classGoddessImplementshit,ieat{//implementing an interface must implement all the methods in the interface     Public voidcry () {System.out.println ("It's killing me."); }     Public voideat () {System.out.println ("A little bite from a small stutter."); }}classGirlImplementshit{ Public voidcry () {System.out.println ("Your Sister!" The pain of the mother ~ "); }}Abstract classPersonImplementshit{}

 Public classMain { Public Static voidMain (string[] args) {//The parent class is large, and the sub-class is small "upward transformation: Reference to the parent class to the subclass object"person S1 =NewMan (); S1.say (); //If there is no say method in the person class, you cannot callS1.talk ();//Call the Talk method in the man class, not the talk method in the person class, and if there is no talk method in the man class , call the Talk method in the person classPerson S2 =Newwoman ();                        S2.say (); //"Transformation down: Converting a parent class instance to a subclass instance (cast)"Man W1 =(man) s1;        W1.say (); //Mans w2 = (man) s2;    }  }/*** Polymorphism: 1. Overloading and overriding of methods 2. The polymorphism of the object*/Abstract classperson{String name; Abstract  Public voidsay ();  Public voidTalk () {System.out.println ("Hi I ' m a person."); }}classMansextendsperson{ Public voidsay () {System.out.println ("I ' m a man."); }     Public voidTalk () {System.out.println ("Hi I ' m a man."); }}classWomanextendsperson{ Public voidsay () {System.out.println ("I ' m a woman."); }}

/*** instanceof Keyword: Used to determine whether an object is an instance of a class, returns a Boolean value*/ Public classMain { Public Static voidMain (string[] args) {Man M1=NewMan ();        Say (M1); Woman m2=NewWoman ();    Say (m2); }     Public Static voidsay (person p) {P.say (); if(pinstanceofWoman) {Woman W=(Woman) p;        W.getangry (); }    }}classperson{ Public voidsay () {System.out.println ("I ' m a person."); }}classMansextendsperson{ Public voidsay () {System.out.println ("I ' m a man."); }}classWomanextendsperson{ Public voidsay () {System.out.println ("I ' m a woman."); }     Public voidgetangry () {System.out.println ("I ' m angrying ..."); }}/*** Parent Design Law * Can be instanceof keyword, we can easily check the object type, but if a parent class is too many subclasses, this kind of judgment is very cumbersome * How to design the parent class? * 1. The parent class is typically designed as an abstract class or interface, where the interface is preferred, and the abstract class * 2 is considered if the interface is not satisfied. A specific class does not inherit another concrete class as much as possible, and the benefit is that there is no need to check whether the object is a parent class object*/

/*** Abstract Applications (Griffin Palace Recruitment) * Template method pattern: Defines the skeleton of an algorithm in an operation, and delays the implementation of some mutable parts into subclasses. * Template method pattern allows subclasses to redefine some specific steps of the algorithm without altering the structure of an algorithm*/ Public classMain { Public Static voidMain (string[] args) {linjiugong LP=NewShemale ("Fish7");    Lp.action (); }}Abstract classlinjiugong{ Public voidAction () {//Recruitment Activities        if(competition ()) {System.out.println ("Congratulations, Welcome to Linjiugong!"); }Else{System.out.println ("Sorry ..."); }    }     Public Abstract BooleanCompetition ();//Abstract Methods}classShemaleextendslinjiugong{PrivateString name; Shemale (String name) { This. Name =name; }     Public BooleanCompetition () {//How to achieve the gameSystem.out.println ("Game start ....") I ' m gonna win! "); Random R=NewRandom (); returnR.nextboolean (); }}

Java Note 6__ abstract class/interface/polymorphic/instanceof keyword, parent design rule