Broken hashset key.java

public static void main(String[] args) {
        Set<Student> set = new HashSet<Student>();
        Student s = new Student("Маша", "Иванова");
        set.add(s);
        s.setName("Даша");
        set.add(s);
        System.out.println(set.size());
    }

 class Student{
        private String name;
        private String surname;

        Student(String name, String surname) {
            this.name = name;
            this.surname = surname;
        }

        String getName() {
            return name;
        }

        void setName(String name) {
            this.name = name;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            Student student = (Student) o;

            if (!name.equals(student.name)) return false;
            if (!surname.equals(student.surname)) return false;

            return true;
        }

        @Override
        public int hashCode() {
            int result = name.hashCode();
            result = 31 * result + surname.hashCode();
            return result;
        } 
 }