Problem

The code provided below was written by a student who was challenged to write a program that reversed every word in a provided sentence. After testing it successfully with a single word, the student was confident that the code would work for a full sentence. Unfortunately, that is not the case. Find all the bugs in the student's code, and fix them. Hint: There are three of them.

import javax.swing.JOptionPane;

public class WordReversal 
{
    public static void main( String[] args ) 
    {
        int lastSpace = 0; //position of the last space we found
        int nextSpace = 0; //position of the next space
        String result = ""; //final result
        String reversedWord = ""; //temporarily holds a reversed word
        String currWord = ""; //the current word we are reversing

        //get input from the user
        String input = JOptionPane.showInputDialog( "Enter a sentence:" );

        //keep looping until we no don't find a new space
        while( nextSpace >= 0 )
        {
            //finds the next space in the sentence
            nextSpace = input.indexOf( ' ', lastSpace );

            if( nextSpace != -1 ) 
            {
                //space was found, grab the word between the spaces
                currWord = input.substring( lastSpace, nextSpace + 1 );
            } 
            else 
            {
                //no more space was found, just grab the rest of the sentence
                currWord = input.substring( lastSpace, input.length() );
            }

            //reverse the word
            for( int j = currWord.length() - 1; j >= 0; j-- ) 
            {
                reversedWord = reversedWord + currWord.charAt( j );
            }

            //add the reversed word to the result so far
            result = result + reversedWord;
        }

        //output the result
        JOptionPane.showMessageDialog( null, result, "Reversed Words",
                JOptionPane.INFORMATION_MESSAGE );
    }
}

String Methods and Debugging

Solution

The solution...

Code

Solution Code

import javax.swing.JOptionPane;

public class WordReversal 
{
    public static void main( String[] args ) 
    {
        int lastSpace = 0;
        int nextSpace = 0;
        String result = "";
        String reversedWord = "";
        String currWord = "";

        String input = JOptionPane.showInputDialog( "Enter a sentence:" );
        while( nextSpace >= 0 ) 
        {
            nextSpace = input.indexOf( ' ', lastSpace + 1 );

            if( nextSpace != -1 ) 
            {
                currWord = input.substring( lastSpace, nextSpace + 1 );
            } 
            else 
            {
                currWord = input.substring( lastSpace, input.length() );
            }

            reversedWord = "";
            for( int j = currWord.length() - 1; j >= 0; j-- ) 
            {
                reversedWord = reversedWord + currWord.charAt( j );
            }

            result = result + reversedWord;
            lastSpace = nextSpace;
        }

        JOptionPane.showMessageDialog( null, result, "Reversed Words",
                JOptionPane.INFORMATION_MESSAGE );
    }
}