Cows And Bulls in Java

import javax.swing.*;
import javax.swing.table.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;

/*
* Title: Cows and Bulls in Java
* Author: Nitish
* Date Created: 20/03/2012
* Last Modified: 22/03/2012
* All Files => https://sites.google.com/site/nitishspblog/test/CowsAndBulls.zip
*/

class CowsBullsScratch extends JFrame implements ActionListener{
JButton submit;
JTextField input;
JLabel word,chanceslbl;
ArrayList<String> words;
ArrayList<String> entered_words;
BufferedReader br;
String selected_word=null;
JScrollPane jsp;
JTable table;
DefaultTableModel model;
int chances=10;

    CowsBullsScratch(){
        super("Cows and Bulls");

        //Initialize GUI components
        setLayout(null);

        submit=new JButton("Submit");
        submit.addActionListener(this);
        submit.setBounds(170,20,100,30);
        add(submit);

        input=new JTextField(10);
        input.setBounds(20,20,150,30);
        add(input);

        //Fetch words from file and randomly select one
        words=new ArrayList<String>();
        try{
        br=new BufferedReader(new FileReader(new File("cbdata.txt")));
            while((selected_word=br.readLine())!=null) {
                words.add(selected_word);
            }
        }
        catch(Exception e){
            e.printStackTrace();
        }
        selected_word=words.get(new Random().nextInt(words.size()));

        word=new JLabel("Word length :"+Integer.toString(selected_word.length()));
        word.setBounds(300,20,100,30);
        add(word);

        chanceslbl=new JLabel("Chances remaining: "+Integer.toString(chances));
        chanceslbl.setBounds(400,20,200,30);
        add(chanceslbl);

        String[] columns = {"Word","Bulls","Cows"};
        Object[][] data = {};

        //Override isCellEditable to make Jtable non editable
        model=new DefaultTableModel(data,columns){
            public boolean isCellEditable(int row, int column) {
                return false;
            }
        };
        table=new JTable(model);
        jsp=new JScrollPane(table);
        jsp.setBounds(20,70,500,200);
        add(jsp);

        setSize(550,350);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);

        entered_words=new ArrayList<String>();
        //JOptionPane.showMessageDialog(this, "The word is "+selected_word);
    }


    public static void main(String args[]){
        new CowsBullsScratch();
    }

    public void actionPerformed(ActionEvent e){
        String st=input.getText();
        st=st.trim();
        if(st.length()!=selected_word.length()){
            JOptionPane.showMessageDialog(this, "Invalid length");
            return;
        }

        if(entered_words.contains(st)){
            JOptionPane.showMessageDialog(this, "You have already entered that word");
            return;
        }

        if(st.equals(selected_word)){
            JOptionPane.showMessageDialog(this, "Congratulations! You guessed the word correctly.");
            return;
        }

        chances--;

        int cows=0;
        int bulls=0;

        //calculate bulls

        for(int i=0;i<selected_word.length();i++){
            if(selected_word.charAt(i)==st.charAt(i)){
                bulls++;
            }
        }


        //remove duplicate characters from input and store the result in tmp
        ArrayList<Character> tmp=new ArrayList<Character>();
        for(int i=0;i<st.length();i++){
            if(!tmp.contains(st.charAt(i))){
                tmp.add(st.charAt(i));
            }
        }

        //calculate cows
        for(int i=0;i<tmp.size();i++){
            char c=tmp.get(i);
            int last_index=0;

            //iterate till the string doesn't contain character c
            //with each iteration narrow down the search space
            //This process can be made simpler by comparing characters individually
            //I guess I was experimenting with something which made this process more complex
            while(true){
                int index=selected_word.indexOf(c,last_index);

                if(index==-1){
                    break;
                }
                else{
                    cows++;
                }
                last_index=index+1;
            }
        }

        entered_words.add(st);

        //update GUI
        input.setText("");
        chanceslbl.setText("Chances remaining:"+Integer.toString(chances));
        model.insertRow(model.getRowCount(),new Object[]{st,  new Integer(bulls), new Integer(cows-bulls)});

        if(chances<=0){
            JOptionPane.showMessageDialog(this, "You Lost! The word was "+selected_word);
        }

    }
}