input: Write a function to convert a Java code snippet to Python 3. The Java code snippet is provided as input. If the input is in the correct format, return the corresponding Python 3 code. If the input is not valid, return an error message.
  assert convert_java_to_python("""public class Foo {
    public int foo( int a, int b ) {
      return a + b;
    }
  }""") == "def foo(a, b):\n return a + b"
  assert convert_java_to_python("""public class Bar {
    public int bar( int x, int y ) {
      return x * y;
    }
  }""") == "def bar(x, y):\n return x * y"
  assert convert_java_to_python("""public class Invalid {
    public invalid( int a, int b ) {
      return a + b;
    }
  }""") == "Error: Invalid Java code snippet."
  assert convert_java_to_python("") == "Error: Input is empty."
output: def convert_java_to_python(java_code):
      if not java_code:
          return "Error: Input is empty."
      
      import re
      match = re.match(r'public class \w+ {\s+public int (\w+)\( int (\w+), int (\w+) \) {\s+return \w+ \w+ \w+;\s+}\s+}', java_code)
      
      if match:
          func_name, param1, param2 = match.groups()
          return f"def {func_name}({param1}, {param2}):\n return {param1} {match.group(0)[match.group(0).find('return')+7:match.group(0).find(';')]} {param2}"
      else:
          return "Error: Invalid Java code snippet."