Why are transient fields needed in Java and how do they work during serialization?

Hi everyone! I'm learning Java and came across the `transient` modifier for class fields. I read the documentation but still don't fully understand why it's needed.\n\nI have a simple user class:\n\n```java\npublic class User implements Serializable {\n private String username;\n private String password;\n private int age;\n\n // getters and setters\n}\n```\n\nWhen I serialize an object of this class to a file, I want to save username and age, but I don't want to save password — it's confidential data! I tried simply not writing password manually, but during deserialization the password field turns out to be `null`, which breaks the authentication logic.\n\nQuestions:\n1. How to properly exclude password from serialization so that after deserialization I can restore it (for example, from another source)?\n2. P