Java serialization String == and equals

Question

I write an object to a file and then I read it.

Then I make "if" to compare object's arguments. For example "genreDescription" is "Action".

 if (genreDescription == "Action" ) {
  System.out.println("Some text");
        }

Before import == and equals produce expected and the same result. After import equals work but == doesn't. I tried removing blank spaces. I also manually updated object's "genreDescription" to "Action" right before if. It affects only String, because if "gendreDescription" is int like 6 then it's normal. Why?