need help sorting a string array alphabetically

[Jere Johnson]

I can't seem to get this program to sort. Not sure why. Can anyone see a problem with my bubble sort?
thanks.

 
import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class Assignment8b extends Applet implements ActionListener
{
private Button add, display, sort;
private TextField input;
private int j;
private String [] stringArray = new String [10];
private boolean clickedYet = false;
private boolean displayNow = false;

public void init()
{
//add button
add = new Button ("Add");
add(add);
add.addActionListener(this);

//display button
display = new Button ("Display");
add(display);
display.addActionListener(this);

//search button
sort = new Button ("Sort");
add(sort);
sort.addActionListener(this);

//input textField
input = new TextField (20);
add (input);
input.addActionListener (this);
}
public void paint(Graphics g){

g.drawString ("Array output below",50,75);
g.drawLine (50,80,150,80);

if (displayNow)
display (stringArray, g);

}

public void actionPerformed (ActionEvent event)
{
clickedYet = true;

if (clickedYet){

if (event.getSource() == add)
addData (stringArray);

if (event.getSource() == display)
displayNow = true;

if (event.getSource() == sort)
  sort (stringArray);
}

input.setText(null);

repaint ();

}

// This section below contains the methods to carry out the tasks 1,2 and 3

public void addData (String [] array)

{array[j++] = input.getText();  }

public void display(String [] array, Graphics g)  
{    
  int yValue=110;    
  
  for (int w=0; w < array.length; w++)  
  {    g.drawString("Index "+w+" is "+array[w], 70, yValue);      
  yValue +=20;    }  
  }
  
   
  //bubble sort 
public void sort(String [] array)
   {
   String temp;
   
   for (int pass=0; pass < (array.length - 1); pass++)
   for (int i=1; i < (array.length - pass); i++)
   if (array[i].compareTo(array[i-1]) > 0)
   {
   temp = array [i];
   array [i] = array [i - 1];
   array [i-1] = temp;
   
   }
   
   }
     
  


} // end of program
 

[Maulin Vasavada]

hi
this algo seems sorting in descending order. if u want to have ascending order sorting then change the comparision if() u 've like...
if ( a[i].compareTo(a[i-1]) < 0 )..
it shd work...
regards
maulin

[Balaji Natarajan]

Everything is Correct with ur code...the only thing is u haven't checked for null values while displaying and sorting...added those two checks...check whether it is working or not

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Assignment8b extends Applet implements ActionListener{
private Button add, display, sort;
private TextField input;private int j;
private String [] stringArray = new String [10];
private boolean clickedYet = false;
private boolean displayNow = false;
public void init(){
//add button
add = new Button ("Add");
add(add);
add.addActionListener(this);
//display button
display = new Button ("Display");
add(display);
display.addActionListener(this);
//search button
sort = new Button ("Sort");
add(sort);
sort.addActionListener(this);
//input textField
input = new TextField (20);
add (input);
input.addActionListener (this);
}
public void paint(Graphics g){
g.drawString ("Array output below",50,75);
g.drawLine (50,80,150,80);
if (displayNow)
display (stringArray, g);
}
public void actionPerformed (ActionEvent event){
clickedYet = true;
if (clickedYet){
if (event.getSource() == add)
addData (stringArray);
if (event.getSource() == display)
displayNow = true;
if (event.getSource() == sort)
sort (stringArray);
}
input.setText(null);
repaint ();
}
// This section below contains the methods to carry out the tasks 1,2 and 3
public void addData (String [] array) {
array[j++] = input.getText();
}
public void display(String [] array, Graphics g) {
int yValue=110;
for (int w=0; w < array.length; w++) {
if(array[w]!=null) {
g.drawString("Index "+w+" is "+array[w], 70, yValue);
yValue +=20;
}
}
}
//bubble sort
public void sort(String [] array) {
String temp;
for (int pass=0; pass < (array.length - 1); pass++)
for (int i=1; i < (array.length - pass); i++)
if(array[i]!=null) {
if (array[i].compareTo(array[i-1]) > 0) {
temp = array [i];
array [i] = array [i - 1];
array [i-1] = temp;
}
}
}
}
// end of program

[Dirk Schreckmann]

Of course, the easy way is to just use java.util.Arrays.sort()

[chi Lin]

Jeremiah.
First, due to the uninitialized stringArray[], NullPointer exception was thrown when sort() method was called (check with MS-DOS for this exception). I put one line into init()
to initialize stringArray... current inital value is "".
for(int i=0;i<stringArray.length;i++)
stringArray[i]="";
Second, as I dont really see why the sort() does not work as expected, I made some changes on the index inside the for loop of the sort() in a way I know how sorting is done,

public void sort(String [] array){
  String temp;
  for(int pass=0;pass < array.length - 1; pass++)
    for(int i=pass+1;i<array.length;i++)
      if (array[pass].compareTo(array[i]) > 0)
      {
temp = array [i];
   array [i] = array [pass];
   array [pass] = temp;
      }
}   

then re-run the applet, the result is not perfect, but sorting is on the way.
HTH
[ April 24, 2003: Message edited by: chi Lin ]

[Jere Johnson]

Chi,
I tried it your way, but it seems like the sorting jumps about 8 index's down the array.
not sure why
your statement did get me somewhere. Thanks for that.
[ April 24, 2003: Message edited by: Jeremiah Coleman ]

[Joel McNary]

Just as an aside, since I'm not sure what your assignment entails, I would suggest using a List instead of an Array to hold your Strings and then sorting your list.
Your sorting algorithm works fine, but as Balaji pointed out, the sortwing was failing when it encountered a null value in the Array. It woudl therefore do some sorting, but stop when it got the NullPointerException. If you filled the array with 10 variables it worked fine (albiet reversed; see Maulin's post).
in general, you would still have to check for null, but in this instance you cnnot put null values into the list (just empty strings). And as an added benefit, you List is not limited to 10 entries. You can add as many as you like (and then see the performance difference between bubble-sorting 10 items and 300 items )

[Jere Johnson]

Thanks you to everybody who replied. I appreciate your time.
I tried the if (array[i]!=null) and it worked