Uses of readObject/writeObject in Serialization

Question

I was going through this article to understand more about Java Serialization process. When it comes to uses of readObject/writeObject I could see two use cases:

Answer 1

public class Employee implements Serializable {

    private static final long serialVersionUID = 1L;

    private int empno;
    private String ename;
    private String job;

    // setter & getter

    @Override
    public String toString() {
        return "Employee [empno=" + empno + ", ename=" + ename + ", job=" + job
                + "]";
    }

    private void writeObject(ObjectOutputStream out) throws IOException {

        // default serialization
        // out.defaultWriteObject();

        // custom serialization
        out.writeInt(empno);
        out.writeUTF(ename);
        // out.writeUTF(job); //job will not serialize
    }

    private void readObject(ObjectInputStream in) throws IOException,
            ClassNotFoundException {

        // default deSerialization
        // in.defaultReadObject();

        // custom deSerialization
        empno = in.readInt();
        ename = in.readUTF();
        // this.job = in.readUTF();
    }

}