Thread: Sorting LinkedList

Im trying to do a bubble sort style process to my linkedList. It is a LinkedList of assignments, each with a set date stored as a string. I want to order the linkeList by the the date in which they were set. I can convert the strings to dates and compare them, my problem seems to be with changing the position of the assignments when i find out of they are in the incorrect order. Im using the index of the item in the linkedList to change the position as you will see below.

    public void orderSet()  
        {  
            SimpleDateFormat ValidFormat = new SimpleDateFormat("dd/MM/yyyy");  
            ListIterator<Assignment> iterator = assignmentList.listIterator(1);  
 
            boolean sorted = false;  
            while(!sorted)  
            {  
                while(iterator.hasNext())  
                {  
                    firstIndex = assignmentList.indexOf(iterator.previous());  
                    String previousDate = assignmentList.get(firstIndex).getDateSet();  
 
                    try  
                    {  
                        date = ValidFormat.parse(previousDate);  
                    }  
                    catch(ParseException pe)  
                    {  
                        System.out.println("ParseException" + pe);  
                    }  
 
                    index = assignmentList.indexOf(iterator.next());  
                    String checkSetDate = assignmentList.get(index).getDateSet();  
 
                    try  
                    {  
                        dateCheck = ValidFormat.parse(checkSetDate);  
                    }  
                    catch(ParseException pe)  
                    {  
                        System.out.println("ParseException" + pe);  
                    }  
 
                    if(dateCheck.before(date))  
                    {  
                        int temp = iterator.previousIndex();
                        int current = index;
                        int previous = current;
 
                        assignmentList.set(previous,assignmentList.get(index));
                        assignmentList.set(temp,assignmentList.get(firstIndex));  
 
                    }  
                }  
            }  
        }

Can you print out the list before the sort and again after the sort to show what the code is doing?

Let us know when you have working code to test.
Or try debugging the code yourself. If you don't use an interactive debugger, add lots of println statements to show execution flow and the values of variables as they are changed.

the while loop and found out its just running through an infinite loop

Now you need to print out the values of the variables that are causing the infinite loop Then try to see why the code does not change them to allow the loop to exit.

hasNext() will stay true until you remove all the items from the iterator.

How can I test it?

Can you make a small simple program that compiles and execute and shows the problem. Hardcode the data into the program so no extra files are required.

Sorry its a bit of a mess, i usually seperate them into seperate files. It compiles and runs in the same way as before though.

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.LinkedList;
import java.util.ListIterator;
 
public  class SortingLL  {
    private String MTitle;
    private String MIdentifier;
    private String ATitle;
    private String DateSet;
    private String DueDate;
    private String AAuthor;
    private String Weighting;
    static LinkedList<SortingLL> assignmentList;
    static Date date;
    static Date dateCheck;
    static Date tempDate;
    static int index;
    static int firstIndex;
 
    public SortingLL(String MTitle, String MIdentifier, String ATitle, String DateSet, String DueDate, String AAuthor, String Weighting)
    {
        this.MTitle = MTitle;
        this.MIdentifier = MIdentifier;
        this.ATitle = ATitle;
        this.DateSet = DateSet;
        this.DueDate = DueDate;
        this.AAuthor = AAuthor;
        this.Weighting = Weighting;        
    }
 
    public String getDateSet()
    {
        return DateSet;
    }
 
    public void setDateSet(String DateSet)
    {
        this.DateSet = DateSet;
    }
 
    public String toString()     {
//        return  MTitle + "\n" + MIdentifier + "\n" + ATitle + "\n" + DateSet + "\n" + DueDate + "\n" + AAuthor + "\n" + Weighting + "\n";
        return  MTitle + " " + MIdentifier + "  " + ATitle + "  " + DateSet + "  " + DueDate + "  " 
                  + AAuthor + "  " + Weighting + "\n";
    }
 
    public static class Registry
    {
 
        public Registry()
        {
            assignmentList = new LinkedList<SortingLL>();
        }
 
        public void addAssignment(SortingLL aAssignment)
        {
            assignmentList.add(aAssignment);
        }
 
        public void orderSet()
        {
            SimpleDateFormat ValidFormat = new SimpleDateFormat("dd/MM/yyyy");
            ListIterator<SortingLL> iterator = assignmentList.listIterator(1);
 
            boolean sorted = false;
            while(!sorted)
            {
                while(iterator.hasNext())                 {
                    firstIndex = iterator.previousIndex();
                    String previousDate = assignmentList.get(firstIndex).getDateSet();
 
                    try                      {
                        date = ValidFormat.parse(previousDate);
                    }
                    catch(ParseException pe)                    {
                        System.out.println("ParseException" + pe);
                    }
 
                    index = assignmentList.indexOf(iterator.next());
                    String checkSetDate = assignmentList.get(index).getDateSet();
 
                    try                     {
                        dateCheck = ValidFormat.parse(checkSetDate);
                    }
                    catch(ParseException pe)                     {
                        System.out.println("ParseException" + pe);
                    }
 
 //                   System.out.println("Testing inner while loop");
                    System.out.println("previous date = " + previousDate + " current date = " + checkSetDate);
 
                    if(dateCheck.before(date))                     {
                        int previous = firstIndex;//Index of previous assignment
                        int current = index; // Index of current assignment
 
                        SortingLL temporary = assignmentList.get(firstIndex);
 
                       // System.out.println("tempIdx =" + temp + " int currentIdx= " + current);
                        System.out.println("setting previous=" + previous + " to " + assignmentList.get(index));
                        assignmentList.set(previous, assignmentList.get(index));
                        System.out.println("setting current=" + current + " to " + temporary);
                        assignmentList.set(current, temporary);
 
                    }
                }
                sorted = true;
            }
            System.out.println("After aL=" + assignmentList.toString());
        }
    }
 
    public static void main(String[] args)      {
        Registry newAssignment = new Registry();
        newAssignment.addAssignment(new SortingLL("Java 1","ASM 1001","Java assignment 1","28/02/2012","10/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 2","ASM 1002","Java assignment 2","27/02/2012","19/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 3","ASM 1003","Java assignment 3","23/02/2012","22/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 4","ASM 1004","Java assignment 4","29/02/2012","22/05/2012","Mr Joe Bloggs","20%"));
 
        System.out.println("Before aL=" + SortingLL.assignmentList.toString());
 
        System.out.println("Testing sort");
        System.out.println("************\n");
 
        newAssignment.orderSet();
 
 
    }
 
}

I see two dates. Which date is it supposed to sort on?

I changed the debug print out to give more info:

 
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.LinkedList;
import java.util.ListIterator;
 
public  class SortingLL  {
    private String MTitle;
    private String MIdentifier;
    private String ATitle;
    private String DateSet;
    private String DueDate;
    private String AAuthor;
    private String Weighting;
    static LinkedList<SortingLL> assignmentList;
    static Date date;
    static Date dateCheck;
    static Date tempDate;
    static int index;
    static int firstIndex;
 
    public SortingLL(String MTitle, String MIdentifier, String ATitle, String DateSet, String DueDate, String AAuthor, String Weighting)
    {
        this.MTitle = MTitle;
        this.MIdentifier = MIdentifier;
        this.ATitle = ATitle;
        this.DateSet = DateSet;
        this.DueDate = DueDate;
        this.AAuthor = AAuthor;
        this.Weighting = Weighting;        
    }
 
    public String getDateSet()
    {
        return DateSet;
    }
 
    public void setDateSet(String DateSet)
    {
        this.DateSet = DateSet;
    }
 
    public String toString()     {
//        return  MTitle + "\n" + MIdentifier + "\n" + ATitle + "\n" + DateSet + "\n" + DueDate + "\n" + AAuthor + "\n" + Weighting + "\n";
        return  MTitle + " " + MIdentifier + "  " + ATitle + "  " + DateSet + "  " + DueDate + "  " 
                  + AAuthor + "  " + Weighting + "\n";
    }
 
    public static class Registry
    {
 
        public Registry()
        {
            assignmentList = new LinkedList<SortingLL>();
        }
 
        public void addAssignment(SortingLL aAssignment)
        {
            assignmentList.add(aAssignment);
        }
 
        public void orderSet()
        {
            SimpleDateFormat ValidFormat = new SimpleDateFormat("dd/MM/yyyy");
            ListIterator<SortingLL> iterator = assignmentList.listIterator(1);
 
            boolean sorted = false;
            while(!sorted)
            {
                while(iterator.hasNext())                 {
                    firstIndex = iterator.previousIndex();
                    String previousDate = assignmentList.get(firstIndex).getDateSet();
 
                    try                      {
                        date = ValidFormat.parse(previousDate);
                    }
                    catch(ParseException pe)                    {
                        System.out.println("ParseException" + pe);
                    }
 
                    index = assignmentList.indexOf(iterator.next());
                    String checkSetDate = assignmentList.get(index).getDateSet();
 
                    try                     {
                        dateCheck = ValidFormat.parse(checkSetDate);
                    }
                    catch(ParseException pe)                     {
                        System.out.println("ParseException" + pe);
                    }
 
 //                   System.out.println("Testing inner while loop");
                    System.out.println("previous date = " + previousDate + " current date = " + checkSetDate);
 
                    if(dateCheck.before(date))                     {
                        int temp = firstIndex;//Index of previous assignment
                        int current = index; // Index of current assignment
                        int previous = current; //
 
                       // System.out.println("tempIdx =" + temp + " int currentIdx= " + current);
                        System.out.println("setting temp=" + temp + " to " + assignmentList.get(index));
                        assignmentList.set(temp, assignmentList.get(index));
                        System.out.println("setting current=" + current + " to " + assignmentList.get(firstIndex));
                        assignmentList.set(current, assignmentList.get(firstIndex));
 
                    }
                }
                sorted = true;
            }
            System.out.println("After aL=" + assignmentList.toString());
        }
    }
 
    public static void main(String[] args)      {
        Registry newAssignment = new Registry();
        newAssignment.addAssignment(new SortingLL("Java 1","ASM 1001","Java assignment 1","28/02/2012","10/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 2","ASM 1002","Java assignment 2","27/02/2012","19/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 3","ASM 1003","Java assignment 3","23/02/2012","22/05/2012","Mr Joe Bloggs","20%"));
        newAssignment.addAssignment(new SortingLL("Java 4","ASM 1004","Java assignment 4","29/02/2012","22/05/2012","Mr Joe Bloggs","20%"));
 
        System.out.println("Before aL=" + SortingLL.assignmentList.toString());
 
        System.out.println("Testing sort");
        System.out.println("************\n");
 
        newAssignment.orderSet();
 
 
    }
 
}

Hopefully studying what is printed out will show you what is happening.

The code loses the first element and has two copies of the 3rd.
Time for some design work with a paper and pencil.

You need to post the code that shows the logic and that can be executed for testing.

One thing I see is that you are printlng out the values that are being tested: if(dateCheck.before(date))

For solving these kinds of problems you must use paper and pencil and work through your logic. In the code add enough printlns to see what is happening and then compare it with what you have worked out on paper.

For solving these kinds of problems you must use paper and pencil and work through your logic. In the code add enough printlns to see what is happening and then compare it with what you have worked out on paper.v