Implementing Java DAO Pattern on the Same JVM

This question is related to the core understanding of the Java DAO Pattern. Please look at a simple java dao pattern example to understand my question.

At line 2 below, the student object has already been altered with a new name, what is the point of line three if both the client and the backend are running under the same JVM?

In my humble understanding of the DAO pattern, the client must only alter data using services, such as the studentDao below, and the client shouldn't have the possibility of altering the value object (pojo) directly. But when both the client and the backend service run under the same JVM, and client gets a POJO with normal setters, why does the client need to call the service?

Are there any best practices to implement a DAO pattern where the client can and must only consume/alter data using dao-services? A very example would be great to look at.

//update student
1. Student student =studentDao.getAllStudents().get(0);
2. student.setName("Michael");
3. studentDao.updateStudent(student);