Java Retrieve or Remove a value from TreeMap -

i have problem retrieving student's info list, or deleting it... heelp... code below:

import java.util.*; public class directory {     private treemap<string, student> studentlist;     private int numberofentries;      public directory()     {         studentlist = new treemap<string, student>();         numberofentries = 0;     }      public void addstudent(student newstudent)     {         studentlist.put(newstudent.studentinfo(), newstudent);         //numberofentries++;     }      public void studentinfo(string studentinfo)     {         object obj = studentlist.get(studentinfo);         system.out.println(obj);     }      public void removestudent(string studentinfo)     {         object obj = studentlist.remove(studentinfo);         system.out.println(obj + "removed");     }       public void printstudentlist()     {         system.out.println("list of students: " + studentlist.keyset());     } } 

======= student class ======== (persons contains first, last & email)

public class student extends persons {     private string sclass;      public student(string lname, string fname, string email, string sclass)     {         super(lname, fname, email);         this.sclass = sclass;     }      public string studentinfo()     {         return " full name " + lastname + " " + firstname + "\n" +                 "e-mail: " + email + "\n" +                "class attending: " + sclass;     }      public string getname()     {         return lastname;     } } 

i try , debug you, defeat purpose. (this your homework ... , purpose you learn how yourself.)

my advice follows:

1. first fix style errors:

   • the names of variables should always start lower-case letter ... unless static final constants.

   • the names of methods should always start lower-case letter

   • method , variable names should meaningful , consistent. instance:

     public void  removestudent(string studentinfo) 

     here studentinfo needs student name, not "student info" string created strudentinfo method ...

     another example: lname , fname not meaningful. (i can guess mean, not enough.)

2. create tester program created instances of classes , performs sequence of tests on them. start simple things, move on more complicated ones.

   (in real world, we'd set more formal set of "unit tests" ... not ready yet.

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in fact, if choose more meaningful names, , carefully @ how names used, error should "leap out , hit on nose".

but maximum benefit if go through process yourself.