Java I/O and collection have been written for a long time.

Import Java. io. *; <br/> Import Java. util. *; </P> <p> public class test6_map {<br/> Public static void main (string [] ARGs) {<br/> mymapstu MMS = new mymapstu (new file ("exp.txt"); <br/> system. out. println ("Enter the student ID of the content you want to find! "); <Br/> Using SC = new using (system. in); <br/> long SnO = SC. nextlong (); <br/> Student stu2 = new student (SNO, ""); <br/> If (MMs. containskey (stu2) {<br/> system. out. println ("the name is" + MMs. get (stu2.getno (); </P> <p >}else {<br/> system. out. println ("No such person! "); <Br/>}</P> <p> class student {// simple definition of student class <br/> private long SnO; <br/> private string sname; </P> <p> Public student () {<br/>}< br/> Public student (long SnO, string sname) {<br/> This. sno = SnO; <br/> This. sname = sname; <br/>}</P> <p> Public long getno () {<br/> return SnO; <br/>}< br/> Public String getname () {<br/> return sname; <br/>}</P> <p> class mymapstu {// This class is defined mainly Connect to the file and read the data to map. <Br/> Map <long, string> map; </P> <p> Public mymapstu (File stuinfo) {<br/> If (! Stuinfo. exists () {<br/> try {<br/> stuinfo. createnewfile (); <br/> system. out. println ("Please create a student information table with 30 students! "); <Br/> bufferedwriter Fos = new bufferedwriter (New outputstreamwriter (New fileoutputstream (stuinfo); <br/> byte [] bytes = new byte [40]; <br/> for (INT I = 0; I <30; I ++) {<br/> bufferedreader BR = new bufferedreader (New inputstreamreader (system. in); <br/> string STR = new string (); <br/> STR = BR. readline (); <br/> FOS. write (STR, 0, str. length (); <br/> FOS. newline (); <br/>}< br/> FOS. close (); <br/>} Cat CH (ioexception e) {<br/> E. printstacktrace (); <br/>}</P> <p> try {<br/> map = new hashmap <long, string> (); <br/> bufferedreader FD = new bufferedreader (New inputstreamreader (New fileinputstream (stuinfo); <br/> string stmp; <br/> while (stmp = Fi. readline ())! = NULL) {<br/> system. out. println (stmp); <br/> string [] sarray = stmp. split (""); <br/> Student Stu = new student (Long. parselong (sarray [0]), sarray [1]); <br/> map. put (Stu. getno (), Stu. getname (); <br/>}< br/> FCM. close (); <br/> system. out. println (MAP); <br/>} catch (ioexception e) {<br/> E. printstacktrace (); <br/>}</P> <p> Public Boolean containskey (student Stu) {<br/> If (map. containskey (Stu. getno () {<br/> return true; <br/>} else {<br/> return false; <br/>}</P> <p> Public String get (long SnO) {<br/> If (map. containskey (SNO) {<br/> return map. get (SNO); <br/>}else {<br/> return NULL; <br/>}</P> <p>}