------classes and objects of Java

MyDate class

public class mydate{private int year, month, day;      private static int thisyear=2015;     Public mydate (int year, int month, Int. day) {this.year=year;    This.month=month;   This.day = day; Public MyDate () {this (1970,1,1);//date new Date ()--long} public mydate (MyDate d) {//this=d;//th   IS is a final variable and cannot be changed by the value this (D.year, D.month, D.day);     } public void Set (int year, int month, Int. day) {//algorithm imperfect this.year = year; This.month = (month>=1 && month<=12)?     Month:1; This.day = (day>=1 && day<=31)?   Day:1;   } public void Set (MyDate d) {this.set (d.year, D.month, D.day);   } public void Setyear (int.) {this.year = year;   } public void setmonth (int month) {this.month = month;   } public void Setday (int day) {this.day = day;   } public int GetYear () {return this.year;   } public int GetMonth () {return this.month;   } public int GetDay () {return this.day; } public static int getthisyear () {return thisyear=java.util.calendar.getinstance (). get (Java.util.Calendar.YEAR);   The public String toString () {return this.year+ "year" +this.month+ "month" +this.day+ "Day"; public static Boolean isleapyear (int year) {//In a static method, a direct non-static method cannot be called.     If it is, it must be adjusted by the (new) object. Boolean Boo=year%400==0 | |     year%100!=0&&year%4==0;   return boo;   } public boolean isleapyear () {return this.isleapyear (this.year);  } public static int daysofmonth (Int. year,int month) {switch (month) {case 1:case 3:case 5:case 7:case 8:       Case 10:case 12:return 31;       Case 4:case 6:case 9:case 11:return 30; Case 2:return isleapyear (year)?       29:28;     Default:return 0;   }} public int daysofmonth () {return daysofmonth (this.year,this.month);     } public void Tomorrow () {this.day++;      if (This.day > This.daysofmonth ()) {day = 1;      month++;        if (month>12) {this.month=1;       this.year++;   }  }} public MyDate Yestoday () {mydate yes = new MyDate (this);     yes.day--;     if (yes.day<1) {yes.month--;     if (yes.month==0) {yes.month=12;     yes.year--;     } Yes.day = Daysofmonth (yes.year,yes.month);   } return yes; }}

Person class

Class person{protected String name;protected mydate birthday;protected static int count=0;  Public person (String name, mydate birthday) {  this.name = name;  this.birthday= birthday;  count++;  }  Public person (person p) {This  (p.name, New MyDate (P.birthday));//Deep copy} public person  () {This  ("nameless", NE W mydate ());  }    public void Set (String name) {  this.name = name;  }  public void set (MyDate birthday) {  this.birthday = birthday;   }  public int getage () {  return (Mydate.getthisyear ()-birthday.getyear ());  }  Public String GetName () {  return this.name;  }  Public MyDate Getbirthday () {  return this.birthday;  }  public int oldthen (person p) {  return  p.birthday.getyear ()-this.birthday.getYear ();  }    public static void Howmany () {  System.out.println (count+ ' Person object ');  }    Public String toString () {  return name + "," + this.birthday.toString ();  }   }

Studen class

public class Student extends person{private string number;//Learn No: 0101 0001private string speciality;private static in  T count;//variable hides private static int max=0; Public Student (String name,mydate birthday,string speciality) {super (Name,birthday);//Must be in the first sentence this.speciality =  speciality;  Processing number max++;  String str = "+max";  int n = str.length (); str = str.substring (n-4,n);    [n-4,n-1] This.number = "0101" +mydate.getthisyear () +str;  count++;  } public Student (person p, String speciality) {This (P.getname (), P.getbirthday (), speciality);  } public Student (String name, mydate birthday) {This ("nameless", New MyDate (), "");  } public Student () {This ("nameless", New MyDate (), "unemployed");  } public Student (Student s) {This (S.name, S.birthday, s.speciality); }//set, the Get//method overrides (the subclass exists exactly the same way as the parent class), the permissions of the subclass method cannot be lower than the parent class public String toString () {return number+ "," +name+ "," +birthday     . toString () + "," +speciality;  }//method overloads public void set (String speciality) {this.speciality = speciality; } PUBlic static void Howmany () {///static method is not allowed direct access: This or Super System.out.println ("Number of person objects:" +person.count); System.out.println ("Number of Student objects:" +count);    This.count} public void Finalize () {count--;     } public static void Main (String args[]) {person P1 = new person ("Ted", New MyDate (1995,4,20));     Student S1 = new Student (P1, "Computer");     Student s2 = new Student (s1);//compile-time polymorphic s2.set ("Java");          S2.howmany ();     person P2 = new Student (s2);//Run-time polymorphic, new who tune who//student s3 = new Person ();//Wrong System.out.println (p2.tostring ());          System.out.println ("---------");     Person ps[] = {P1,S1,S2,P2};     for (int i=0; i<ps.length; i++) {System.out.println (ps[i]);     } System.out.println ("---------");     Object objs[] = {P1,S1,S2,P2};     for (Object obj:objs) {System.out.println (obj); }        }}

------classes and objects of Java