What is wrong with this class? Please help

Question

I'm trying to sort a dynamically created JComboBox into Alphabetical order. However, the class below is the result of my coding and there is a problem. the code can sort only two(2) item in the JComboBox and no more which is wrong. I do not know where i'm going wrong in the selectionSort(JComboBox cmb) method. the getLargest(JComboBox cmb) method works perfectly because i have tried it. Can somebody please take a look at my codes and help me modify it.
Thanks
James
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class SortCombo extends JFrame implements ActionListener{
JButton btnAdd, btnSort;
JComboBox cmbItems;
JTextField text1;
public SortCombo(){
super("Sorting Demo");
this.getContentPane().setLayout(new GridLayout(4,1));
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
btnAdd = new JButton("Add Item to Combo Box");
btnSort = new JButton("Sort Items in ComboBox");
text1 = new JTextField(20);
cmbItems = new JComboBox();
btnAdd.addActionListener(this);
btnSort.addActionListener(this);
this.getContentPane().add(cmbItems);
this.getContentPane().add(text1);
this.getContentPane().add(btnAdd);
this.getContentPane().add(btnSort);
this.pack();
this.show();
public void actionPerformed(ActionEvent e){
if(e.getSource() == btnAdd){
String s = text1.getText();
if (!s.equals("") && !isDuplicate(s,cmbItems))
cmbItems.addItem(text1.getText());
}else if(e.getSource() == btnSort){
selectionSort(cmbItems);
// int i = getLargest(cmbItems);
// System.out.println(i);
public boolean isDuplicate(String stationName, JComboBox cmb){
int j = cmb.getItemCount();
boolean result = false;
for (int i = 0; i < j; i++){
String s = (String)cmb.getItemAt(i);
if (stationName.trim().equalsIgnoreCase(s.trim()))
result = true;
return result;
public int getLargest(JComboBox cmb){
int indexSoFar = 0;
int size = cmb.getItemCount();
for(int currIndex = 1; currIndex < size; currIndex++){
String strSoFar = (String)cmb.getItemAt(indexSoFar);
String currStr = (String)cmb.getItemAt(currIndex);
char charSoFar = strSoFar.charAt(0); charSoFar = Character.toUpperCase(charSoFar);
char currChar = currStr.charAt(0); currChar = Character.toUpperCase(currChar);
if(currChar > charSoFar){
indexSoFar = currIndex;
return indexSoFar;
public void selectionSort(JComboBox cmb){
int n = cmb.getItemCount();
for (int last = n-1; last >=1; last--){
int largest = getLargest(cmb);
String temp = (String)cmb.getItemAt(largest);
String temp2 = (String)cmb.getItemAt(last);
cmb.removeItemAt(largest);
cmb.insertItemAt(temp2,largest);
cmb.removeItemAt(last);
cmb.insertItemAt(temp,last);
public static void main(String[] args){
new SortCombo();
}

Answer 1

I beleive what is wrong is that your getLargest method returns the largest to your selection sort.The selectionSort places the largest at the end.On the next iteration it finds the largest again. this time at the end where you put it.Now it just does the same thing over again placing the same item at the end until the loop runs out.What you are left with is only one item it the right spot(sometimes 2).I could not get it to work the way you had it here so I tried a rewrite.It seems to work ok but it won't sort two words that start with the same letter properly.You may have to insert an algorithm to fix this.I got rid of the getLargest method and did everything in the selectionSort method.I used what I think is called a bubble sort but I'm not sure.
I hope this is what you were looking for:)
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class SortCombo extends JFrame implements ActionListener{
     JButton btnAdd, btnSort;
     JComboBox cmbItems;
     JTextField text1;
     public SortCombo(){
          super("Sorting Demo");
          getContentPane().setLayout(new GridLayout(4,1));
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          btnAdd = new JButton("Add Item to Combo Box");
          btnSort = new JButton("Sort Items in ComboBox");
          text1 = new JTextField(20);
          cmbItems = new JComboBox();
          btnAdd.addActionListener(this);
          btnSort.addActionListener(this);
          Container pane = getContentPane();
          pane.add(cmbItems);
          pane.add(text1);
          pane.add(btnAdd);
          pane.add(btnSort);
          pack();
          show();
     public void actionPerformed(ActionEvent e){
          if(e.getSource() == btnAdd){
          String s = text1.getText();
          if (!s.equals("") && !isDuplicate(s,cmbItems))
          cmbItems.addItem(text1.getText());
          }else if(e.getSource() == btnSort){
          selectionSort(cmbItems);
     public boolean isDuplicate(String stationName, JComboBox cmb){
          int j = cmb.getItemCount();
          boolean result = false;
          for (int i = 0; i < j; i++){
               String s = (String)cmb.getItemAt(i);
               if (stationName.trim().equalsIgnoreCase(s.trim()))
               result = true;
          return result;
     public void selectionSort(JComboBox cmb){
          int count = cmb.getItemCount();
          for(int start = 0;start < count;start++){
               for(int x = start;x < count-1;x++){
                    String first = (String)cmb.getItemAt(start);
                    String next = (String)cmb.getItemAt(x+1);
                    char charFirst = first.charAt(0);
                           charFirst = Character.toUpperCase(charFirst);
                    char charNext = next.charAt(0);
                    charNext = Character.toUpperCase(charNext);
                         if(charFirst > charNext){
                              String temp  = (String)cmb.getItemAt(start);
                              String temp2 = (String)cmb.getItemAt(x+1);
                              cmb.removeItemAt(start);
                              cmb.insertItemAt(temp2,start);
                              cmb.removeItemAt(x+1);
                              cmb.insertItemAt(temp,x+1);
     public static void main(String[] args){
          new SortCombo();
}p.s.(I removed the "this" references from your constructor when I rewrote it because they are implied anyway)
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