Serialization process constantly overwrites itself?

I'm fairly new to java and trying to do some serialization in my project. I have a bunch of objects called Student and I would like to serialize them. The code I'm using for this is as follows:

  try{
for(Student s: students){ 
FileOutputStream fileOut = new FileOutputStream("C:/Users/Jaimee-Lee/Desktop/Advanced programming work/MilestoneOne/student.ser");
ObjectOutputStream out = new ObjectOutputStream(fileOut);
out.writeObject(s);
out.close();
fileOut.close();
}
System.out.printf("Serialized data is saved in /MilestoneOne/student.ser \n");
}catch(IOException i){
i.printStackTrace();
}

The issue I'm finding is that the students array I'm using has twenty students (S1 - S20). When I attempt to deserialize the objects, it only gives me the object that contains the last student to have been serialized (S20)

This is my deserialization code:

for(Student student : students){
System.out.println(student.getStudentID());
}
try(FileInputStream fis = new FileInputStream("student.ser");
ObjectInputStream ois = new ObjectInputStream(fis)){
while(fis.available() > 0 ){
deserializedStudents.add((Student) ois.readObject());
System.out.println("Added");
}
System.out.println(Arrays.toString(deserializedStudents.toArray()));
deserializedStudents.forEach(student -> System.out.println(student.getStudentID()));
}catch(IOException | ClassNotFoundException exc){
exc.printStackTrace();
}

I have also noticed that when I open the .ser file, that there is only one line in it. I'm assuming this may be evidence that it is in fact overwriting itself every time as my understanding is that there should be as many lines as there objects in the serialization file.

Can anyone help me to understand what I am doing that is causing the file to overwrite itself instead of retaining objects that have already been added?

Also, here is my Student class for reference:

import java.io.Serializable;
public class Student implements Serializable{
private static final long serialVersionUID = 1L;
// Class Attributes
private String studentID;
private String rankings;
private char personalityType;
private String conflict;
private String preferences;
// Class Constructor
public Student(String ID){
this.studentID = ID;
}
public Student(String ID, String grades) {
this.studentID = ID;
grades = grades.trim();
this.rankings = grades;
}
public Student(String ID, String ranking,char personality){
this.studentID = ID;
this.rankings = ranking;
this.personalityType = personality;
}
// Accessor Methods
public String getStudentID() {
return this.studentID;
}
public String getRankings(){
return this.rankings;
}
public String getPreferences(){
return this.preferences;
}
public char getPersonalityType(){
return this.personalityType;
}
public String getConflict(){
return this.conflict;
}
//Modifier Methods
public boolean setPreferences(String pref){
this.preferences = pref;
return true;
}
public boolean setGrades(String grades){
this.rankings = grades;
return true;
}
public boolean setPersonalityType(char pers){
this.personalityType = Character.toUpperCase(pers);
return true;
}
public boolean setConflict(String ids){
this.conflict = ids;
return true;
}
@Override
public String toString(){
return studentID + ";" + rankings + ";" + personalityType + ";" + conflict + ";" + preferences; 
}
}

for(Student s: students){ 
FileOutputStream fileOut = new FileOutputStream("C:/Users/Jaimee-Lee/Desktop/Advanced programming work/MilestoneOne/student.ser");
ObjectOutputStream out = new ObjectOutputStream(fileOut);
out.writeObject(s);
out.close();
fileOut.close();
}

You're creating a new FileOutputStream inside the for-loop, overwriting the old information with each iteration. Don't do this, create the stream before the loop and use it within the loop:

FileOutputStream fileOut = new FileOutputStream("C:/Users/Jaimee-Lee/Desktop/Advanced programming work/MilestoneOne/student.ser");
ObjectOutputStream out = new ObjectOutputStream(fileOut);
for(Student s: students){ 
out.writeObject(s);
}
out.close();

And close it after the loop.

There are a few things your doing wrong, first your closing and opening the output streams when you write each record, you want to open it before and close it after writing the data.

I took a look at the .ser file - it appears to be binary, so if you try to open it up an look at it, depending on what sort of editor you use, it may or may not show interisting information.

heres a working example of what you want to do.
it worked fine on java 8
'
package serTest;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
public class Student 
implements Serializable{
public String Name;
public String Id;
public String Major;
public boolean 	active;
public int		years;
Student(){
Name 	= "";
Id		= "";
Major	= "";
active	= true;
years	= 0;
}
Student(String Nam,String id,String major,boolean act,int yrs){
Name 	= Nam;
Id		= id;
Major	= major;
active	= act;
years	= yrs;
}
public static void main(String argv[]) {
List<Student> myStudents = new ArrayList<Student>();
myStudents.add(new Student("Mike","140","Art"		,true,1));
myStudents.add(new Student("Greg","142","Partying"	,false,2));
myStudents.add(new Student("Lori","145","Business"	,true,3));
myStudents.add(new Student("Burt","157","Eng"		,true,4));
Student.toFile("Students.ser",myStudents);
List<Student> theStudents = Student.frFile("Students.ser");
}
static List<Student> frFile(String fSpec){
List<Student>	Students = new ArrayList<Student>();
try{
FileInputStream fis = new FileInputStream(fSpec);
ObjectInputStream ois = new ObjectInputStream(fis);
while(fis.available() > 0 ){
Students.add((Student) ois.readObject());
System.out.println("Added");
}
System.out.println(Students.size()+" students read");
Students.forEach(student -> System.out.println(student.Name));
return Students;
}
catch(IOException | ClassNotFoundException exc){
exc.printStackTrace();
}
return null;
}
static boolean toFile(String fSpec,List<Student> students) {
try{
FileOutputStream 	fileOut =	 new FileOutputStream(fSpec);
ObjectOutputStream 	out = 		new ObjectOutputStream(fileOut);
for(Student s: students){ 
out.writeObject(s);;
}
out.close();
fileOut.close();
System.out.printf("Serialized data is saved in "+fSpec);
}
catch(IOException i){
i.printStackTrace();
return false;
}
return true;
}
}

`