Linked List for custom insertion sorting not listing

Question

Hello fellow humans! :3 this is an assignment; the little menu's options are the tasks it's supposed to perform. Sadly, case 1 only records the last valid (non -1) entry instead of building a list. case 2 does the same, except for actually recording the ending value (-1) instead of the last valid entry. Cases 3 and 4 are completely useless without the first two; I've included them because being quite new I'd rather not exclude anything important.
class with main method follows:
package batch2;
import java.io.*;
class e21
public static void main (String []args) throws IOException, NumberFormatException
BufferedReader input = new BufferedReader (new InputStreamReader (System.in));
FromKeyboard key = new FromKeyboard();
int a, option = 0, lrg;
MyList alist, blist, clist;
char fin = 'v';
boolean avac, bvac, cvac, bord;
NodeLD nodeaux = null;
alist = new MyList();
blist = new MyList();
clist = new MyList();
do{
  System.out.println("Please choose an option:");
  System.out.println("1. Create list 'A' sorting by insertion");
  System.out.println("2. Create list 'B', unsorted");
  System.out.println("3. Sort list 'B'");
  System.out.println("4. Mix lists 'A' & 'B' into a new sorted list 'C'");
  System.out.println("9. Exit");
  option = key.enterInt();
  switch (option){
  case 1: //this only records the last valid (non -1) entry D:
         System.out.println("Enter the integers you wish you sort in list 'A'");
      System.out.println("To finish, enter '-1'");
      a = key.enterInt();
      if (a != -1){
        alist.insertToList(a);
        System.out.println("Test 1");     
      while (a != -1){
           a = key.enterInt();
        if (a != -1){
          System.out.println("Test 1.1");
          nodeaux = new NodeLD();
          nodeaux.theData(a);
          alist.sortInserList(nodeaux);
          System.out.println("Test 2, a="+a+"");
     System.out.println("List 'A', sorted by insertion:");
      alist.seeList();
    break;               
  case 2: //this also keeps the last value, yet not a valid one but the '-1' for the ending condition
         System.out.println("Enter the integers you wish to add to list 'B'");
         System.out.println("Enter '-1' to finish");
         a = 0;
         while (a != -1){
            if (a != -1){
              a = key.enterInt();
              clist.insertToList(a);
         System.out.println("Unsorted list:");
         clist.seeList();
    break;
  case 3:
        while (clist.front != null){
      if (clist.front != null){
         blist.sortInserList(clist.front);
         clist.front = clist.front.givePrevious();
      System.out.println("List 'B', sorted");
      blist.seeList();
    break;
  case 4:
        while (blist.front != null){
     if (blist.front != null){
      alist.sortInserList(blist.front);
      blist.front = blist.front.givePrevious();
     System.out.println("List 'C', combining 'A' & 'B', sorted");
     clist.seeList();
    break;
  case 9:
     System.out.println("Program ended");
    break;
  default:
     System.out.println("Invalid option");
    break;
while (option != 9);
}Custom list class follows:
package batch2;
class MyList
boolean tag = false;
protected NodeLD front;
protected int size;
public MyList(){
     front = null;
     size = 0;
public void insertToList(int x){
     NodeLD t;
     t = new NodeLD();
     t.theData(x);
     t.theNext(front);
     if(front!=null){
          front.thePrevious(t);
     front = t;
     size++;
public void seeList(){
     NodeLD g;
     g = front;
     System.out.println();
     while (g!=null){
       System.out.println(""+g.dat+"");
       g = g.givePrevious();
     System.out.println("=============================");
public int sortInserList(NodeLD g){
     NodeLD pointer = new NodeLD();
     pointer = front;
     NodeLD prepointer = new NodeLD();
     System.out.println("Test A");
     while (g.dat > pointer.dat && pointer != null){
       if (pointer.giveNext()!= null){
        pointer = pointer.giveNext();
        tag = false;
        System.out.println("Test A.b");
       else if (pointer.giveNext() == null) {
        tag = true;
        System.out.println("Test A.c");
       break;
     prepointer = pointer.givePrevious();
     if (pointer == null || tag){
       insertToList(g.dat);
       System.out.println("Test B. Pointer == null or tag == true");
     if (prepointer != null && !tag){
       g.thePrevious(prepointer);
       prepointer.theNext(g);
       System.out.println("Test C. prepointer != null && !tag");
     if (pointer != null && !tag){
       g.theNext(pointer);
       pointer.thePrevious(g);          
       System.out.println("Test D. pointer !=null && !tag");
     System.out.println("Test E. Right before return");
     return g.dat;
}And here comes the accompanying Node class:
package batch2;
class NodeLD
private int data;
private NodeLD next;
private NodeLD previous;
public int dat;
NodeLD(){
     data = 0;
     next = null;
     previous = null;
     dat = data;
public void theData(int x){
     data = x;
     dat = data;
public void theNext(NodeLD y){
     next = y;
public void thePrevious(NodeLD z){
     previous = z;
public int giveData(){
     return data;
public NodeLD giveNext(){
     return next;
public NodeLD givePrevious(){
     return previous;
}And last but not least, the part of FromKeyboard I'm using for this exercise, just in case:
package batch2;
import java.io.*;
public class FromKeyboard
public BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
public int enterInt(){
     System.out.flush();
     int integ = -1;
     try{
          integ = Integer.valueOf(input.readLine());
     catch(NumberFormatException e){
          System.err.println("Error: "+e.getMessage()+"");
     catch(IOException t){
          System.err.println("Error: "+t.getMessage()+"");
     return integ;
}All help with regards as to why my lists aren't working and general comments/nudges on the sorting are welcome and appreciated.

Answer 1

Hi Kevin, thank you for replying! I'll trim my code in a moment; as for a specific inquiry:
>Sadly, case 1 only records the last valid (non -1) entry instead of building a list. case 2 does the same, except for actually recording the ending value (-1) instead of the last valid entry. >
More direct approach to asking for help: These classes compile correctly and run, although the result is not what I'm aiming for: I get a single-noded list instead of the full list. Why isn't it keeping all the nodes but the last one only?
Edited by: SquaredCircle on 09-Sep-2010 16:46
That was fun :D this is my SSCCE for the main class:
class e21SSCCE
public static void main (String []args) throws NumberFormatException
int a[] = {14, 25, 11, 43, 33, -1}, key[] = {1,2,9}, option = 0, i = 0, e = 0;
MyList alist, clist;
char fin = 'v';
NodeLD nodeaux = null;
alist = new MyList();
clist = new MyList();
do{
  System.out.println("Please choose an option:");
  System.out.println("1. Create list 'A' sorting by insertion");
  System.out.println("2. Create list 'C', unsorted");
System.out.println("9. Exit");
  option = key[e];
  e++;
  switch (option){
  case 1: //this only records the last valid (non -1) entry D:
         System.out.println("Enter the integers you wish you sort in list 'A'");
      System.out.println("To finish, enter '-1'");
      i = 0;
      if (a[i] != -1){
        alist.insertToList(a);
     i++;
     while (a[i] != -1){
if (a[i] != -1){
     nodeaux = new NodeLD();
     nodeaux.theData(a[i]);
     alist.sortInserList(nodeaux);
     i++;
     System.out.println("List 'A', sorted by insertion:");
     alist.seeList();
break;               
case 2: //this also keeps the last value, yet not a valid one but the '-1' for the ending condition
System.out.println("Enter the integers you wish to add to list 'B'");
System.out.println("Enter '-1' to finish");
i = 0;
while (a[i] != -1){
if (a[i] != -1){
clist.insertToList(a[i]);
                    i++;     
System.out.println("Unsorted list:");
clist.seeList();
break;
case 9:
     System.out.println("Program ended");
break;
default:
     System.out.println("Invalid option");
break;
while (option != 9);
The cleaner version of the list class:class MyList
boolean tag = false;
protected NodeLD front;
protected int size;
public MyList(){
     front = null;
     size = 0;
public void insertToList(int x){
     NodeLD t;
     t = new NodeLD();
     t.theData(x);
     t.theNext(front);
     if(front!=null){
          front.thePrevious(t);
     front = t;
     size++;
public void seeList(){
     NodeLD g;
     g = front;
     System.out.println();
     while (g!=null){
          System.out.println(""+g.dat+"");
          g = g.givePrevious();
     System.out.println("=============================");
public int sortInserList(NodeLD g){
     NodeLD pointer = new NodeLD();
     pointer = front;
     NodeLD prepointer = new NodeLD();
     while (g.dat > pointer.dat && pointer != null){
          if (pointer.giveNext()!= null){
               pointer = pointer.giveNext();
               tag = false;
          else if (pointer.giveNext() == null) {
               tag = true;
               break;
          prepointer = pointer.givePrevious();
          if (pointer == null || tag){
               insertToList(g.dat);
          if (prepointer != null && !tag){
               g.thePrevious(prepointer);
               prepointer.theNext(g);
          if (pointer != null && !tag){
               g.theNext(pointer);
               pointer.thePrevious(g);          
     return g.dat;
And the node class:class NodeLD
private int data;
private NodeLD next;
private NodeLD previous;
public int dat;
NodeLD(){
     data = 0;
     next = null;
     previous = null;
     dat = data;
public void theData(int x){
     data = x;
     dat = data;
public void theNext(NodeLD y){
     next = y;
public void thePrevious(NodeLD z){
     previous = z;
public int giveData(){
     return data;
public NodeLD giveNext(){
     return next;
public NodeLD givePrevious(){
     return previous;
I followed the SSCCE guideline, and tried my best with it. The indentation checker was a broken link, though :c.
Edited by: SquaredCircle on 09-Sep-2010 17:12