Java learning instance, implement empty object, and rewrite, Comparator class implements the comparison to the container!

Less nonsense, on the code: this is the code I study, if useful, I hope to help everyone! Striving for each example is involved in the new technology, new knowledge points!

Like to follow my blog: Http://blog.csdn.net/happylaoxu

Talk less nonsense, on the code:

Package Com.xuyaowen.student;import java.util.*;//uses an empty object to implement the Rtti form; interface Null{}class student{public static int allnum=0;private int id;private String name;private int age; Student () {System.out.println ("This is the form of an ordinary object");} Student (int id, String name, int age) {allnum++;this.id = Id;this.name = Name;this.age = age;} Public String toString () {return ' ID ' + this.id + ' Name ' + this.name + ' age ' + this.age;} public void modifyage (int addnum) {System.out.println ("You are modifying the age!") "); this.age = This.age + addnum;} public int getage () {return this.age;} public int getId () {return this.id;} Public String GetName () {return this.name;} public static class Nullstudent extends Student implements Null {private nullstudent () {super (0, "none", 0);} Public String toString () {return ' Nullperson ';}} public static final Student NULL = new Nullstudent ();//This can be called directly student.null; That can be achieved,}//defines a comparison interface; class Studentidcomparator implements Comparator<student>{public int compare (Student STD1, Student std2) {return (Std1.getId ()-Std2.getid ());}} Class Studentagecomparator implements Comparator<student>{public int compare (Student std1, Student std2) {return ( Std1.getage ()-std2.getage ());}} Class Admin{private linkedlist<student> students = new linkedlist<student> (); Admin () {System.out.println ("Start student admin mode! ");} Add a student; public void addstudent (Student std) {students.add (STD); SYSTEM.OUT.PRINTLN ("Successfully added student:" +std.getname ());} Increase the age of all; public void addage (int num) {if (num<0) {System.out.println ("Age should be positive!") ");} Else{for (Student a:students) {a.modifyage (num);} SYSTEM.OUT.PRINTLN ("Age increased" + num);}} Get the number of people older than 20; public int getNum20 () {int count = 0;for (Student a:students) {if (A.getage () >20) {count++;}} System.out.println ("The current student is older than 20 has" + count + "person"); return count;} Operation by ID to sort the students public void sortstudents (String tag) {if ("id" = = tag) {System.out.println ("You are sorted by id"); Collections.sort (students, New Studentidcomparator ());//Sort by ID,}else if ("age" = = tag) {Collections.sort (students, New STUDENTAGECOmparator ());//Use the age to sort System.out.println ("You are sort of as old");} else{System.out.println ("Warning! This class cannot be sorted by" + tag + ");}} Public String toString () {StringBuilder result = new StringBuilder (), for (Student a:students) {result.append (a.tostring ( + ""); Result.append (' \ n ');//The line break is really going to be parsed out! }return result.tostring ();}} public class School {public static admin admin = new Admin ();p rivate static Scanner scan = new Scanner (system.in);p ublic The static void Main (string[] args) {System.out.println ("This program only involves interface presentation and does not involve the interaction of the program!") "); Scan.nextline (); System.out.println ("This is a test of the Student Class"), Admin.addstudent (New Student (123, "Jack0"), Admin.addstudent (New Student (125, " Jack2, Admin.addstudent (New Student (121, "Jack3"), Admin.addstudent (New Student ("Jack4", 20)); Admin.addstudent (New Student (124, "Jack5"), Admin.addstudent (New Student (126, "Jack6", 21)); System.out.println (admin); Scan.nextline (); System.out.println ("Sort by Student ID:"); Admin.sortstudents ("id"); System.out.println (admin); Scan.nextline (); System.ouT.println ("Sort by student Age:"), Admin.sortstudents ("age"); System.out.println (admin); Scan.nextline (); System.out.println ("1 increase in age of all students"); Admin.addage (1); System.out.println (admin); Scan.nextline (); System.out.println ("Statistics of persons of all ages greater than 20 years"); Admin.getnum20 (); Scan.nextline (); SYSTEM.OUT.PRINTLN ("Program Interface show end! ");}}

Java learning instance, implement empty object, and rewrite, Comparator class implements the comparison to the container!