我的代码编译但不执行.我哪里做错了？如何在未来的代码中避免这种情况？

我正在尝试将3,999以下的任何罗马数字转换为十进制数.代码编译但从不提示我输入罗马数字,就像扫描仪要求的那样.

//necessary for the scanner  
import java.util.Scanner; 
/**
* conversion of roman numerals into decimals
* 
* @Annika Helverson 
* period 5
*/

public class Numeral
{

private static Scanner scanner = new Scanner( System.in );
public static int decimalValue (String romanNumeral) {
    int decimal = 0;
    int count = 0;
    int i = 1;
  //tell user what to do
System.out.print( "Please enter a valid roman numeral: ");
//read the submitted number
String input = scanner.nextLine();
//display input back to user
System.out.println( "input =" + input );

    while (count < romanNumeral.length ()-1 || i < romanNumeral.length ()){
    if (romanNumeral.substring (count, i).equals ("M")){
        decimal = decimal + 1000;
    }
    if (romanNumeral.substring (count, i).equals ("D")) {
        decimal = decimal + 500;
    }
    if (romanNumeral.substring (count, i).equals ("C")) {
        decimal = decimal + 100;
    }
    if (romanNumeral.substring (count, i).equals ("L")) {
        decimal = decimal + 50;
    }
    if (romanNumeral.substring (count, i).equals ("X")) {
        decimal = decimal + 10;
    }
    if (romanNumeral.substring (count, i).equals ("V")) {
        decimal = decimal + 5;
    }
    if (romanNumeral.substring (count, i).equals ("I")) {
        decimal = decimal + 1;
    }
    count = count + 1;
    i = i + 1;
    } 
    {
    if (romanNumeral.contains ("CM")){
    decimal = decimal - 200;

这里有更多罗马数字中所有"例外"的代码.} return decimal; }}}