Inputting an object of class Student into a program from a file

Question

Hi,
I need to read in objects of a class called "Student" from a file.
The Student class looks like this:
import java.io.Serializable;
public class Student implements Serializable
private int id;
private String lastName;
private String firstName;
private double gpa;
public Student(int a, String b, String c, double d)
id = a;
lastName = b;
firstName = c;
gpa = d;
public int getId()
return id;
public String getlastName()
return lastName;
public String getfirstName()
return firstName;
public double getgpa()
return gpa;
public String toString()
return "ID: " + id + " FIRST NAME: " + firstName + " LAST NAME: " + lastName + " GPA: " + gpa;
I know how to read text from a file, however I do not know how to read an object from a file. I know that the class has to be serializable in order to read in the objects, however I am having trouble reading and saving the objects read into a variable.
Can someone explain or give a same algorithm to do this?
Thanks,
Jackson

Answer 1

Hi,
You will have to use java.io.FileInputStream class to create a file stream where you will be storing the object state and and java.io.ObjectInputStream to actually dump the object state into it.
Further, you have to use java.io.FileOutputStream and java.io.ObjectInputStream to open the file and read back the object state into the Student objects. However, you have to explicitly cast them into Student objects since the return type for the readObject() method is java.lang.Object.
Here is the code where I serialized 2 Student objects and un-serialized them back into the program. (You can do this within different programs, or even different JVM instances).
class serializeDemo
     public static void main(String args[])
          Student s1 = new Student(11, "Hanks", "Tom", 8.55); //creating a student
          Student s2 = new Student(22,"Pitt", "Brad", 7.87); //another student
          try
               // SERIALIZE STUDENT DATA
               FileOutputStream fo = new FileOutputStream("studentSer.ser");
               ObjectOutputStream os = new ObjectOutputStream(fo);
               os.writeObject(s1);
               os.writeObject(s2);
               System.out.println("The student objects have been serialized");
               os.close();
               //UN-SERIALIZE THE SERIALIZED DATA
               FileInputStream fi = new FileInputStream("studentSer.ser");
               ObjectInputStream oi = new ObjectInputStream(fi);
               Student s1_recovered = (Student)oi.readObject();
               System.out.println("Object S1 recovered : " + s1_recovered.getfirstName() + " " + s1_recovered.getlastName());
               Student s2_recovered = (Student)oi.readObject();
               System.out.println("Object S2 recovered : " + s2_recovered.getfirstName() + " " + s2_recovered.getlastName());
               oi.close();
          catch(Exception e)
               e.printStackTrace();
}You can actually try printing the contents of the studentSer.ser file and you will find the object members and their values separated by some non-printable text.
Regards,
Nagendra U M
Edited by: Nagendra_U_M on Mar 30, 2010 11:18 PM