Java Code that will compress and decompress a string.

import java.util.*;
public class practice
{
    public static void main(String args[])
    {
        Scanner scan = new Scanner(System.in);
        String originalString = scan.nextLine();
        String compressedString = "";
        int index = 0;
        int numReps = 0;
        char nextChar = ' ';
        if (args.length==0 || args[0].equals("-c"))
        {
            System.out.println("compress");
            String s = scan.next();
            compress(originalString);
        }
        else if (args[0].equals("-d"))
        {
            System.out.println("decompress");
            decompress(compressedString);
        }
        else
        {
            System.out.println("Error! Unknown mode.");
        }

    }

    public static void compress(String originalString)
    {
        int index = 0;
        int numReps = 0;
        char nextChar = ' ';
        while (index < originalString.length())
        {
            numReps = 0;
            char c = originalString.charAt(index);
            if (!Character.isDigit(c))
            {
                nextChar = c;
                index++;
            }
            else
            {
                while (Character.isDigit(c))
                {
                    int temp = Integer.parseInt(""+c);
                    numReps = temp;
                    index++;
                    if (index >= originalString.length())
                    {
                        break;
                    }
                    c = originalString.charAt(index);
                }
                for (int i =0; i<numReps; i++)
                {
                    System.out.println(nextChar+i);
                }
            }
        }
    }

    public static void decompress(String compressedString)
    {
        int index = 0;
        int numReps = 0;
        char nextChar = ' ';

        while (index < compressedString.length())
        {
            numReps = 0;
            char c = compressedString.charAt(index);
            if (!Character.isDigit(c))
            {
                nextChar = c;
                index++;
            }
            else
            {
                while (Character.isDigit(c))
                {
                    int temp = Integer.parseInt(""+c);
                    numReps = (numReps*10) + temp;
                    index++;
                    if (index >= compressedString.length()) break;
                    c = compressedString.charAt(index);
                }
                for (int i =0; i<numReps; i++)
                {
                    System.out.println(nextChar);
                }
            }
        }
    }
}