java - Having issues with custom linked list and applying to JTable -

i'm having issues creating jtable using custom table model , custom linked list. i'm hoping there easy changes i'm missing.

my main class:

import java.util.arraylist; import java.util.*; import java.io.*; import javax.swing.*; import java.awt.*; import java.awt.event.*; import javax.swing.table.*; public class studentinterface { public static void main(string[] args){         new studentinterface();     }     //create linked list            mylinkedlist studentpack = new mylinkedlist();  public studentinterface (){     //create jframe     jframe jframe = new jframe("student information interface");     jframe.setdefaultcloseoperation(jframe.exit_on_close);     jframe.setsize(400,300);     jframe.setvisible(true);     jframe.setdefaultlookandfeeldecorated(true);     jframe.setpreferredsize(new dimension(600, 400));      //create content panes     jpanel headerpanel = new jpanel();     jpanel tablepanel = new jpanel();     jpanel buttonpanel = new jpanel();     jpanel combinedpanel = new jpanel();     headerpanel.setlayout(new borderlayout());     tablepanel.setlayout(new flowlayout());     buttonpanel.setlayout(new flowlayout());     combinedpanel.setlayout(new borderlayout());      //add label header content panel     jlabel headerlabel1 = new jlabel("welcome student information interface");     jlabel headerlabel2 = new jlabel("***click cell edit data***");     jlabel headerlabel3 = new jlabel("***click column header sort***");     headerlabel1.sethorizontalalignment(jlabel.center);     headerlabel2.sethorizontalalignment(jlabel.center);     headerlabel3.sethorizontalalignment(jlabel.center);     headerpanel.add(headerlabel1, borderlayout.north);     headerpanel.add(headerlabel2, borderlayout.center);     headerpanel.add(headerlabel3, borderlayout.south);      //where gui created:     jmenubar menubar;     jmenu menu, submenu;     jmenuitem exitmenuitem;     jmenuitem savemenuitem;     jmenuitem loadmenuitem;      //create menu bar.     menubar = new jmenubar();      //build main menu.     menu = new jmenu("file");     menu.setmnemonic(keyevent.vk_a);     menu.getaccessiblecontext().setaccessibledescription("the menu in program has menu items");     menubar.add(menu);      //create menu items     exitmenuitem = new jmenuitem("exit",keyevent.vk_t);     menu.add(exitmenuitem);     jframe.setjmenubar(menubar);      //create table     tablemodel model;     model = new tablemodel(new mylinkedlist());     jtable table = new jtable(model);      //add list list content panel     jscrollpane scrollpane = new jscrollpane(table);     scrollpane.setpreferredsize(new dimension(580, 400));     tablepanel.add(scrollpane);      //add buttons button content panel     jbutton addbutton = new jbutton("add");     jbutton removebutton = new jbutton("remove");     buttonpanel.add(addbutton);     buttonpanel.add(removebutton);      addbutton.addactionlistener(new actionlistener() {         public void actionperformed(actionevent e) {         //verify pack not full         int packsize = studentpack.size();         if (packsize >= 10)             {             joptionpane.showmessagedialog(null,             "the interface full. please remove student first.",             "interface full",             joptionpane.warning_message);             return;             }          jpanel p1 = new jpanel(new gridlayout(2,1));         jtextfield t1 = new jtextfield();         jlabel labell = new jlabel("please enter first name of student add:");         p1.add(labell);         p1.add(t1);         joptionpane.showmessagedialog(null,p1,"first name",joptionpane.plain_message);         string userfirstname = t1.gettext();          jpanel p2 = new jpanel(new gridlayout(2,1));         jtextfield t2 = new jtextfield();         jlabel label2 = new jlabel("please enter last name of student add:");         p2.add(label2);         p2.add(t2);         joptionpane.showmessagedialog(null,p2,"last name",joptionpane.plain_message);         string userlastname = t2.gettext();          jpanel p3 = new jpanel(new gridlayout(2,1));         jtextfield t3 = new jtextfield();         jlabel label3 = new jlabel("please enter major of student add:");         p3.add(label3);         p3.add(t3);         joptionpane.showmessagedialog(null,p3,"major",joptionpane.plain_message);         string usermajor = t3.gettext();          jpanel p4 = new jpanel(new gridlayout(2,1));         jtextfield t4 = new jtextfield();         jlabel label4 = new jlabel("please enter netid of student add:");         p4.add(label4);         p4.add(t4);         joptionpane.showmessagedialog(null,p4,"netid",joptionpane.plain_message);         string usernetid = t4.gettext();          jpanel p5 = new jpanel(new gridlayout(2,1));         jtextfield t5 = new jtextfield();         jlabel label5 = new jlabel("please enter gender of student add:");         p5.add(label5);         p5.add(t5);         joptionpane.showmessagedialog(null,p5,"gender",joptionpane.plain_message);         string usergender = t5.gettext();          jpanel p6 = new jpanel(new gridlayout(2,1));         jtextfield t6 = new jtextfield();         jlabel label6 = new jlabel("please enter uin of student add:");         p6.add(label6);         p6.add(t6);         joptionpane.showmessagedialog(null,p6,"uin",joptionpane.plain_message);         string useruin = t6.gettext();          jpanel p7 = new jpanel(new gridlayout(2,1));         jtextfield t7 = new jtextfield();         jlabel label7 = new jlabel("please enter age of student add:");         p7.add(label7);         p7.add(t7);         joptionpane.showmessagedialog(null,p7,"age",joptionpane.plain_message);         string userageinput = t7.gettext();         int userage = integer.parseint(userageinput);          jpanel p8 = new jpanel(new gridlayout(2,1));         jtextfield t8 = new jtextfield();         jlabel label8 = new jlabel("please enter gpa of student add:");         p8.add(label8);         p8.add(t8);         joptionpane.showmessagedialog(null,p8,"gpa",joptionpane.plain_message);         string usergpainput = t8.gettext();         double usergpa = double.parsedouble(usergpainput);          //create student student         student studentstudent = new student(userfirstname, userlastname, usermajor, usergpa, useruin, usernetid, userage, usergender);          //store student in linked list         model.addstudent(studentstudent);         }     });      removebutton.addactionlistener(new actionlistener() {         public void actionperformed(actionevent e) {         //verify pack not full         if (studentpack.size() == 0)             {             joptionpane.showmessagedialog(null,             "the interface empty. please add student first.",             "interface empty",             joptionpane.warning_message);             return;             }          jpanel p9 = new jpanel(new gridlayout(2,1));         jtextfield t9 = new jtextfield();         jlabel label9 = new jlabel("please enter first name of student remove: **case sensitive**");         p9.add(label9);         p9.add(t9);         joptionpane.showmessagedialog(null,p9,"first name",joptionpane.plain_message);         string userfirstname = t9.gettext();          jpanel p10 = new jpanel(new gridlayout(2,1));         jtextfield t10 = new jtextfield();         jlabel label10 = new jlabel("please enter last name of student remove: **case sensitive**");         p10.add(label10);         p10.add(t10);         joptionpane.showmessagedialog(null,p10,"first name",joptionpane.plain_message);         string userlastname = t10.gettext();          //remove student student in linked list         }     });      exitmenuitem.addactionlistener(new actionlistener() {         public void actionperformed(actionevent e) {             system.exit(0);         }     });      //nest button , list panels in combined content panel     combinedpanel.add(headerpanel, borderlayout.north);     combinedpanel.add(tablepanel, borderlayout.center);     combinedpanel.add(buttonpanel, borderlayout.south);      //add combined content panel frame     jframe.add(combinedpanel);     jframe.pack();     jframe.setlocationrelativeto(null);      joptionpane.showmessagedialog(null,     "***click cell edit data*** \n ***click column header sort***", "how edit/sort data", joptionpane.information_message);     }  public class tablemodel extends abstracttablemodel {  public final string[] columnnames = { "first name", "last name", "major:", "gpa", "uin", "netid", "age", "gender" }; private mylinkedlist data;  public tablemodel(mylinkedlist data) {     this.data = data; }  @override public int getcolumncount() {     return columnnames.length; }  @override public string getcolumnname(int column) {     return columnnames[column]; }  @override public int getrowcount() {     return data.size(); }  public void addstudent(student student) {         int row = data.size();         data.add(student);         firetablerowsinserted(row, row);     }  public void removestudent(int i) {         int row = data.size();         data.remove(i);         firetablerowsdeleted(row, row);     }  @override public student getvalueat(int rowindex, int columnindex) {     object student = data.getnode(rowindex);     if (student == null) {         return null;     }     switch (columnindex) {     case 0:         return student.getfirstname();     case 1:         return student.getlastname();     case 2:         return student.getmajor();     case 3:         return student.getgpa();     case 4:         return student.getuin();     case 5:         return student.getnetid();     case 6:         return student.getage();     case 7:         return student.getgender();     default:         return null;     } } } } 

here's class student object:

public class student {     // declare attributes here     string firstname;     string lastname;     string major;     double gpa;     string uin;     string netid;     int age;     string gender;      public student(string newfirstname, string newlastname, string newmajor, double newgpa, string newuin, string newnetid, int newage, string newgender){         setfirstname(newfirstname);         setlastname(newlastname);         setmajor(newmajor);         setgpa(newgpa);         setuin(newuin);         setnetid(newnetid);         setage(newage);         setgender(newgender);     }      //mutators     public void setfirstname(string newfirstname) {         firstname = newfirstname;     }      public void setlastname(string newlastname) {         lastname = newlastname;     }      public void setmajor(string newmajor) {         major = newmajor;     }      public void setgpa(double newgpa) {         gpa = newgpa;     }      public void setuin(string newuin) {         uin = newuin;     }      public void setnetid(string newnetid) {         netid = newnetid;     }      public void setage(int newage) {         age = newage;     }      public void setgender(string newgender) {         gender = newgender;     }      //accessors         public string getfirstname() {         return firstname;     }          public string getlastname() {         return lastname;     }          public string getmajor() {         return major;     }          public double getgpa() {         return gpa;     }          public string getuin() {         return uin;     }          public string getnetid() {         return netid;     }          public int getage() {         return age;     }          public string getgender() {         return gender;     } } 

here's reworked linked list class:

public class mylinkedlist<student>{     private node<student> lastnode;     private int nodecount;      public mylinkedlist(){         this.lastnode = null;         this.nodecount = 0;     }      public int size() {         return nodecount;     }      public boolean isempty() {         return this.nodecount == 0;     }      public void add(student student) {         node<student> currentnode = new node<student>(student);         if (this.lastnode != null) {             currentnode.index = lastnode.index + 1;             currentnode.previousnode = lastnode;             lastnode.nextnode = currentnode;         }else {             currentnode.previousnode = null;             currentnode.index = 0;         }         this.lastnode = currentnode;         this.nodecount++;     }      public student get(int index){         //error handling         if(this.isempty() || index < 0 || index > this.nodecount){             return null;         }         //         node<student> currentnode;         int count = lastnode.index - index;         currentnode = lastnode;          while (count > 0) {             currentnode = currentnode.previousnode;             count--;         }          return currentnode.student;     }      public node<student> getnode(int index){         //error handling         if(this.isempty() || index < 0 || index > this.nodecount){             return null;         }         //         int count = lastnode.index - index;         node<student> currentnode = lastnode;          while (count > 0){             currentnode = currentnode.previousnode;             count--;         }          return currentnode;     }      public boolean insert(student student, int index){         node<student> currentnode;          if (this.getnode(index) != null)             {             node<student> newnode = new node<student>(student);             currentnode = this.getnode(index);             newnode.index = index;              if ( null != currentnode.previousnode )                 {                 currentnode.previousnode.nextnode = newnode;                 newnode.previousnode = currentnode.previousnode;                 }              currentnode.previousnode = newnode;             newnode.nextnode = currentnode;             currentnode = newnode;              while (currentnode.nextnode != null)                 {                 currentnode = currentnode.nextnode;                 currentnode.index++;                 }                  this.nodecount++;                 return true;             }         else             {             return false; // error handling             }     }      public boolean remove(int index){         node<student> currentnode;          if (this.getnode(index) != null){             currentnode = this.getnode(index);              if(currentnode.previousnode != null) {                 currentnode.nextnode.previousnode = currentnode.previousnode;                 currentnode.previousnode.nextnode = currentnode.nextnode;             } else if (currentnode.nextnode != null){                 currentnode.nextnode.previousnode = null;             } else if (this.isempty()){                 this.lastnode = null;             }              while (currentnode.nextnode != null){                 currentnode = currentnode.nextnode;                 currentnode.index--;             }              this.nodecount--;             return true;         }else {             return false;         }     }      private static class node<student>{     public node<student> nextnode = null;     public node<student> previousnode = null;     public int index;     public student student;      public node(student student){         this.student = student;     }     } } 

this...

public class tablemodel extends abstracttablemodel {     //...         @override     public student getvalueat(int rowindex, int columnindex) {         object student = data.getnode(rowindex);         if (student == null) {             return null;         }         switch (columnindex) {             case 0:                 return student.getfirstname();             case 1:                 return student.getlastname();             case 2:                 return student.getmajor();             case 3:                 return student.getgpa();             case 4:                 return student.getuin();             case 5:                 return student.getnetid();             case 6:                 return student.getage();             case 7:                 return student.getgender();             default:                 return null;         }     } } 

is giving me compiler error, because student object , object not have of methods trying use.

the obvious fix use...

@override public student getvalueat(int rowindex, int columnindex) {     student student = data.getnode(rowindex); 

okay, there 2 problems. first getvalueat shouldn't returning student, should returning object , 2 getnode returns node<student>

so instead, should more like...

@override public object getvalueat(int rowindex, int columnindex) {     student student = data.get(rowindex); 

okay, causing compiler error, why? get returns student?

i tracked problem down public class mylinkedlist<student> { ... instead, if make public class mylinkedlist { errors go away.

your mylinkedlist doesn't need generic signature <student>, compiler seeing "generic" token , replacing object in code, get method became public object get(int index) instance of mylinkedlist didn't provide base object start ... yea generics :p

now, end can generate...