input: Write a function that defines a class `StringComparator` which initializes with two strings and has methods to compare the strings and return whether they are equal, different, or similar based on a provided threshold. The `edit_distance` function used in `is_similar` is assumed to be imported.
  
  
  class StringComparator:
      def __init__(self, string1, string2):
          self.string1 = string1
          self.string2 = string2
          
      def is_equal(self):
          return self.string1 == self.string2
      
      def is_different(self):
          return self.string1 != self.string2
      
      def is_similar(self, threshold=0.5):
          distance = edit_distance(self.string1, self.string2)
          max_length = max(len(self.string1), len(self.string2))
          
          return distance / max_length < threshold
  
  assert StringComparator("hello", "hello").is_equal()==True
  assert StringComparator("hello", "world").is_equal()==False
  assert StringComparator("hello", "world").is_different()==True
  assert StringComparator("hello", "hella").is_similar(threshold=0.25)==True
  assert StringComparator("hello", "world").is_similar(threshold=0.25)==False
  assert StringComparator("hello", "").is_similar(threshold=0.75)==False
output: class StringComparator:
      def __init__(self, string1, string2):
          self.string1 = string1
          self.string2 = string2
          
      def is_equal(self):
          return self.string1 == self.string2
      
      def is_different(self):
          return self.string1 != self.string2
      
      def is_similar(self, threshold=0.5):
          distance = edit_distance(self.string1, self.string2)
          max_length = max(len(self.string1), len(self.string2))
          
          return distance / max_length < threshold