Added string methods

StringParser.java

      */
     public static String upperCaseString(String s)
     {
-        return null;
+        return s.toUpperCase();
     }
 
     /**
      * @return String
      */
     public static String lowerCaseString(String s) {
-        return null;
+        return s.toLowerCase();
     }
 
     /**
      * @return String
      */
     public static Character getFirstCharacter(String s) {
-        return null;
+        
+        return s.charAt(0);
     }
 
     /**
      * @return String
      */
     public static Character getNthCharacter(String s, Integer n) {
-        return null;
+        return s.charAt(n);
     }
 
     /**
      * @return String
      */
     public static String upperCaseFirstCharacter(String s) {
-        return null;
+        // take substring of first and append the rest of the string
+        String capitalFirst = s.substring(0, 1).toUpperCase() + s.substring(1);
+        
+        return capitalFirst;
     }
 
     /**
      * @return String
      */
     public static String camelCaseString(String s) {
-        return null;
+        // Split the string by empty space
+        // reconnect to a string
+        String words = "";
+        String[] camelCase = s.toLowerCase().split (" ");
+        
+        for (int i = 0; i < camelCase.length; i ++) {
+            words += camelCase[i].substring(0, 1).toUpperCase() + camelCase[i].substring(1);
+        }
+        
+        return words;
+        
     }
 
     /**
      * @return String
      */
     public static String snakeCaseString(String s) {
-        return null;
+        String words = s.toLowerCase().replace(" ","_");
+        
+        return words;
     }
 
     /**
      * @return String
      */
     public static Integer getLength(String s) {
-        return null;
+        return s.length();
     }
 
     /**
      * @return String
      */
     public static Boolean isEqual(String s1, String s2) {
-        return null;
+        return s1.equals(s2);
     }
 
     /**
      * @return String
      */
     public static Boolean isEqualIgnoreCase(String s1, String s2) {
-        return null;
+        return s1.toLowerCase().equals(s2.toLowerCase());
     }
 }