Java Starts from scratch 12 (construction method)

The main purpose of the construction method is to initialize the properties of the class with the definition of the constructor method class Name {access permission class name {Type 1 parameter 1, type 2 parameter 2, ... {program statement; ...//constructor method does not return a value}} in the declaration of the construction method, the reader must keep the following points in mind:· The name of the construction method must be the same as the class name · The declaration of a constructed method cannot have any declaration of a return value type · You cannot use return to return a value in a construction method

classPerson {PrivateString name;//declaring name Attributes    Private intAge//declaring age attributes     PublicPerson (String name,intAge) {//defining constructor methods for property initialization         This. SetName (name);//Assigning a value to the Name property         This. Setage (age);//Assigning a value to the Age property    }     Public voidTell () {//methods of obtaining informationSystem.out.println ("Name:" + getName () + ", Age:" +getage ()); }    ...     Public voidSetage (intA) {//Set Age        if(A >= 0 && a < 150) {//Add the validation code hereAge =A; }    }} Public classConsDemo02 { Public Static voidMain (String args[]) {person per=NewPerson ("Zhang San", 30);//call a constructor method, passing two parametersPer.tell ();//Output Information    }}

Third, the construction method 3.1, the default constructor method there must be a constructor in each class if a class does not declare an explicit constructor, it automatically generates a constructor that does nothing without a parameter.

 PackageCom.pb.demo2;/** Human*/ Public classperson {//persion for Class name    /** Properties, Name,sex,age*/             PublicString name;//name             PublicString sex;//Sex             Public intAge//Age                        /** Method (behavior)*/            //Eat             Public voidEat (String name) {//Pass in a string type parameterSystem.out.println ( This. name+ "Invite" +name+ "to dine Together"); }            //work             Public voidWork () {System.out.println (name+ "The work of the idea is that work to earn money have food to eat!"); }            //work             Public voidWork (String contect) {System.out.println (name+ "The Work philosophy is:" +contect); }}

The above class does not define a constructor method, but the parameterless constructor is called by default in the object that created the class.

     Public Person () {                        }

     Public Static void Main (string[] args) {        //Create object of person class        hanbing=new person ();  Calling a constructor without arguments}

The overloaded construction method of the constructor method is the same as the normal method:the type or number of arguments is different4.1 Overloaded example of a construction method

 Public Person () {// no parameters }      Public Person (String name) {            // A parameter of this        . Name=name    ;    }  Public Person (String name,int. age ) {        // two parameter this        . Name=name;          This . age=age;    }    

4.2, Example 2

 PackageCom.pb.demo2;/** Film category*/ Public classFilm { PublicString type;//genre, horror film, Love, etc.     PublicString name;//Movie Name     PublicString Director;//Director     PublicString actor;//starring         PublicFilm () {//method of constructing without parameters    }     PublicFilm (String type) {//a parameter         This. type=type; }     PublicFilm (String type, string name, string director, string actor) {//how to construct all parameters         This. Type =type;  This. Name =name;  This. Director =Director;  This. actor =actor; }    //Introduction Method     Publicstring Display () {string msg= "Movie type:" +type+ "\ n" \ +name+ "\ n Director:" +director+ "\ n Starring:" +actor; returnmsg; }}

Test class

 PackageCom.pb.demo2;/** Film Test class*/ Public classFilmtest { Public Static voidMain (string[] args) {System.out.println ("******* normal call ******"); //declaring a Movie objectFilm film=NewFilm (); //for the type of object, name, director, starring assignmentFilm.type= "Shootout film"; Film.name= "Let the Bullets Fly"; Film.director= "Jiang Wen"; Film.actor= "Chow Yun, ge you, Jiang Wen"; //Calling MethodsSystem.out.println (Film.display ()); System.out.println ("************** using construction method ****************"); //declaring a movie object and passing in a parameter by constructing a methodFilm two=NewFilm ("Love film", "Can't Tell The Secret", "Jay Chou", "Jay Chou, Anthony Wong, Gui Lun magnesium");    System.out.println (Two.display ()); }}

Java Starts from scratch 12 (construction method)