input: from typing import List
  
  def read_data_from_json(filename: str) -> List:
      """ Reads data from a JSON file. If the file is not found or the JSON is not 
      valid, appropriate error messages are printed.
      >>> read_data_from_json('example.json')
      [{"key": "value"}, {"another_key": "another_value"}]
      >>> read_data_from_json('non_existent_file.json')
      The file specified does not exist.
      >>> read_data_from_json('invalid_format.json')
      The file specified is not in a valid JSON format.
      """
output:     import json
      import os
  
      if not os.path.exists(filename):
          print("The file specified does not exist.")
          return []
  
      try:
          with open(filename, 'r') as file:
              data = json.load(file)
              return data
      except json.JSONDecodeError:
          print("The file specified is not in a valid JSON format.")
          return []