Type safety: The expression of type ArrayList needs unchecked conversion to conform to ArrayList<Student>? This throws a ClassCastException

I'm still quite new to Java and need a hand working out how to get around my problem.

I'm attempting to write a method to deserialize an object that I have called Student. The method is as follows:

   public void readStudentInfo() {
// Desrializes the student objects into an ArrayList for you to compare against
try{
FileInputStream fis = new FileInputStream("student.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
deserializedStudents = (ArrayList) ois.readObject();
ois.close();
fis.close();
}
catch(IOException ioe){
ioe.printStackTrace();
return;
} catch(ClassNotFoundException c){
System.out.println("Class not found");
c.printStackTrace();
return;
}
for(Student student : deserializedStudents){
System.out.println(student.toString());
}
}

The class Student that it works with is as follows:

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; 
}
}

The ArrayList deserializedStudents is initiated at the top of the class like so: ArrayList<Student> deserializedStudents = new ArrayList<>();

For some reason the following line of readStudentInfo() gives this warning : Type safety: The expression of type ArrayList needs unchecked conversion to conform to ArrayList<Student>Java(16777748)

If I ignore it and run the program regardless, the readStudentInfo() method gives the following error: Exception in thread "main" java.lang.ClassCastException: class Student cannot be cast to class java.util.ArrayList (Student is in unnamed module of loader 'app'; java.util.ArrayList is in module java.base
of loader 'bootstrap')

Can someone please help me to understand why this is happening? I've tried changing the cast in the following line a few times: deserializedStudents = (ArrayList) ois.readObject();. I've also tried changing things around a little where I initiate the ArrayList at the start of the program, but no luck yet.

Clarification: The basic idea here is that I'm trying to deserialize a bunch of Student type objects into an ArrayList so that I can use them again.

Please help!

It seems like you did not serialize a list of Students (which is an own object) but Students one by one. Therefore you should either serialize a list or you should deserialize the Students one by one (by continously calling readObject()).

Try this (using try-with-resources):

public void readStudentInfo() {
try (FileInputStream fis = new FileInputStream("student.ser");
ObjectInputStream ois = new ObjectInputStream(fis)) {
List<Student> deserializedStudents = new ArrayList<>();
while (fis.available() > 0) {
deserializedStudents.add((Student) ois.readObject());
}
deserializedStudents.foreach(student -> System.out.println(student));
} catch(IOException | ClassNotFoundException exc){
exc.printStackTrace();
}        
}