ChallengeThree.java

class Challenge {
 	  private static char[] chars;
		private static int indexOfFirstNonRepeat;
		
		/*
		 * @Param String input - String to be tested for first repeated character
		 * @Return String firstNonRepeatSensitive - String containing single character that represents first
		 * non-repeated character in input string (case-sensitive)
		 */
		public static String firstNonRepeatingLetter(String input) 
		{
			//Init values
			chars = null;
			indexOfFirstNonRepeat = 0;
			
			System.out.println("Input string: " + input);
			
			//Create case-sensitive and case-insensitive versions of input
			String inputSensitive = input;
			String inputInsensitive = input.toLowerCase();
			
			System.out.println("String used for comparison: " + inputInsensitive);
			
			//Check if all characters in string are repeated, if not, proceed.
			if(checkAllRepeated(inputInsensitive))
			{
				System.out.println("String contains all repeated characters");
				return "";
			}
			else
			{
				//Convert insensitive string into char array for comparison
				chars = inputInsensitive.toCharArray();
				char firstNonRepeat = '\0';
				
				//For all chars in array
				for(char c : chars)
				{
					//Check if index of current char is equal to index of last char
					if(inputInsensitive.indexOf(c) == inputInsensitive.lastIndexOf(c))
					{
						//Set value of first non repeated char
						firstNonRepeat = c;
						System.out.println("First none repeat (case-insensitive): " + c);
						//Set index of first non repeated char
						indexOfFirstNonRepeat = inputInsensitive.indexOf(c);
						System.out.println("Index of first none repeat: " + indexOfFirstNonRepeat);
						break;
					}
				}
				
				System.out.println("Sensitive string: " + inputSensitive);
			
				//Use index of case-insensitive repeated char to find case-sensitive char
				char firstNonRepeatSensitive = inputSensitive.charAt(indexOfFirstNonRepeat); 
				
				System.out.println("First none repeated char (case-sensitive): " + firstNonRepeatSensitive);
			
				return Character.toString(firstNonRepeatSensitive);
			}
			
		}
		
		/*
		 * Check if all characters in string are repeated
		 * @Param String input - input string to be tested
		 * @Return boolean
		 */
		public static boolean checkAllRepeated(String input)
		{
			char[] chars = input.toCharArray();
			
			if(chars.length == 1)
			{
				return false;
			}
			
			int n = input.length();
		    for (int i = 1; i < n; i++)
		        if (chars[i] != chars[0])
		            return false;
		 
		    return true;
		}
}