Program that compresses and decompresses a string in Java

Question

I need this code to compress and decompress a string given by the user, to compress the user will type either "java compression -c" or just "java compression". To decompress, it will be "java compression -d". Any help would be appreciated. It will now compile and run; however, when you type in the string it will only print out compress and not the compressed 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);
            System.out.println(compressedString);
        }
        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);
                }
            }
        }
    }

    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);
                }
            }   
        }
    }
}

BTW any reason you are ending `while` loops in your code like here `while (index < input.length());` — Prateek, Oct 04 '13 at 23:10
@Prateek That's how my tutor was telling me to do it.(He couldn't figure this out either.) Are the extra () after length not needed? — gdhc21, Oct 04 '13 at 23:16
Depends on what `input` is. If it is an array then you have to use `.length` because length is a property of array; but if it is `String` then use `length()` as `length()` is a method of `String` Class — Prateek, Oct 04 '13 at 23:19
@Prateek I changed some stuff in the code, does this look better? — gdhc21, Oct 04 '13 at 23:31
@Prateek It compiles now, but I get the error message listed above. — gdhc21, Oct 04 '13 at 23:37
Read accepted solution to this question http://stackoverflow.com/questions/7485670/error-could-not-find-or-load-main-class — Prateek, Oct 04 '13 at 23:41
(1) Don't add the `.java` extension when you're running a Java program. (2) Spell `practice` correctly. — ajb, Oct 04 '13 at 23:42
@gdhc21 Which IDE are you using - might be time to learn about debuggers... — Boris the Spider, Oct 05 '13 at 09:24

score 1 · Answer 1 · answered Oct 04 '13 at 23:08

1

You have forgotten the type argument for your method definitions:

public static void decompress(compressedString)

Should be

public static void decompress(String compressedString)

Or even better

public static void decompress(final String compressedString)

answered Oct 04 '13 at 23:08

Boris the Spider

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What's the difference between the two? Also, can you see anything else wrong with the program? – gdhc21 Oct 04 '13 at 23:42
@gdhc21 `final` declares the method parameter immutable; it's just good practice. – Boris the Spider Oct 05 '13 at 09:23

Prateek · Answer 2 · 2013-10-04T23:20:52.770

There are two things going wrong in your code(As far as I can see):-

public static void decompress(compressedString) should actually be public static void decompress(**String** compressedString). You have to tell the method that the argument it is going to receive is of String type.
In your compress and decompress methods you have while (index < input.length());. Check ; at the end. Do you really want that. You will never execute the while loop because you are terminating it before it even begins.

Program that compresses and decompresses a string in Java

2 Answers2