input: Write a function to port a Java code snippet to Python 3. The function should take the Java code as input and return the equivalent Python 3 code. If the input is not a valid Java code snippet, the function should return an error message.
  assert port_java_code("public class Foo {\n  public int foo( int a, int b ) {\n    return a + b;\n  }\n}") == "def foo(a, b):\n return a + b"
  assert port_java_code("public class Bar {\n  public int bar( int x, int y ) {\n    return x * y;\n  }\n}") == "def bar(x, y):\n return x * y"
  assert port_java_code("") == "Error: Input is not a valid Java code snippet."
  assert port_java_code("invalid code") == "Error: Input is not a valid Java code snippet."
output: def port_java_code(java_code):
      if not java_code.strip():
          return "Error: Input is not a valid Java code snippet."
      
      if "public class" not in java_code or "public int" not in java_code:
          return "Error: Input is not a valid Java code snippet."
      
      try:
          class_name = java_code.split("public class ")[1].split()[0]
          method_name = java_code.split("public int ")[1].split()[0]
          params = java_code.split("(")[1].split(")")[0].split(", ")
          body = java_code.split("{\n")[1].split("}")[0].strip()
          
          python_params = ", ".join(param.split()[-1] for param in params)
          python_body = body.replace("return ", "").strip()
          
          return f"def {method_name}({python_params}):\n return {python_body}"
      except:
          return "Error: Input is not a valid Java code snippet."