How can serialisation/deserialisation break immutability?

Question

I was asked this question in an interview. The interviewer wanted to know how to make an object immutable. and then he asked what if I serialise this object - will it break immu

Answer 1

The dirt-simple answer is

class X implements Serializable {
    private final transient String foo = "foo";
}

The field foo will equals "foo" if the object is newly created, but will be null when deserialized (and without resorting to dirty tricks, you won't be able to assign it).