How to write Array of Object to a file?
7 Message(s) by 3 Author(s) originally posted in java programming
| From: DL |
Date: Monday, May 07, 2007
|
Hi
I have an
array of
object s:
Student[] studentarray;
how do I save studentarray to
file ?
David.
| From: DL |
Date: Monday, May 07, 2007
|
Here is a
class the does the writing, but I am getting exceptions saying
its not
serialize d.etc.
import JAVA.io.*;
public class WriteStudentData { /** Creates a new
instance of WriteStudentData */
public WriteStudentData() {
}
//
method will take the student
list and save it to student.dat file.
public void save(Student[] student)
{
try {
ObjectOutputStream objOut = new ObjectOutputStream(new
FileOutputStream("student.dat"));
objOut.
write Object(student);
objOut.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
wrote in
message :
Hi
I have an array of objects:
Student[] studentarray;
how do I save studentarray to file?
David.
| From: Lew |
Date: Monday, May 07, 2007
|
Please don't top-post, not even to your own posts.
wrote in message:
Here is a class the does the writing, but I am getting exceptions saying
its not serialized.etc.
I doubt very much that any
error message included the word "etc." Are you
certain that you copied and pasted the error messages correctly?
import JAVA.io.*;
public class WriteStudentData {
/** Creates a new instance of WriteStudentData */
public WriteStudentData() {
}
// method will take the student list and save it to student.dat file.
public void save(Student[] student)
{
try {
ObjectOutputStream objOut = new ObjectOutputStream(new
FileOutputStream("student.dat"));
objOut.writeObject(student);
objOut.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
Read the JAVAdocs on JAVA.io.Serializable. It'll explain why you cannot use
ObjectOutputStream yet for the Student type.
Incidentally you get better results on newsgroups if you post an SSCCE.
Without the
source for the Student class in hand we've to guess (correctly)
why you cannot serialize the class.
BTW, there are other ways to write information to a file than serialization.
--
Lew
| From: Robert Larsen |
Date: Monday, May 07, 2007
|
wrote in message:
BTW, there are other ways to write information to a file than
serialization.
Absolutely. In fact you should be very carefull when using serialization.
For example if each student has a
reference to his class (school class
that is) and the school class object has references to the students that
attend that class you may save the entire class when you want to save
one student. Do that for each student in the class and you've a huge
overhead.
The other ways are often better...
XML ,
SQL database ,
flat text files,
binary files. There are lots to choose from.
| From: DL |
Date: Monday, May 07, 2007
|
wrote in message:
Please don't top-post, not even to your own posts.
wrote in message:
Here is a class the does the writing, but I am getting exceptions
saying its not serialized.etc.
I doubt very much that any error message included the word "etc." Are
you certain that you copied and pasted the error messages correctly?
import JAVA.io.*;
public class WriteStudentData {
/** Creates a new instance of WriteStudentData */
public WriteStudentData() {
}
// method will take the student list and save it to student.dat file.
public void save(Student[] student)
{
try {
ObjectOutputStream objOut = new ObjectOutputStream(new
FileOutputStream("student.dat"));
objOut.writeObject(student);
objOut.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
Read the JAVAdocs on JAVA.io.Serializable. It'll explain why you
cannot use ObjectOutputStream yet for the Student type.
Incidentally you get better results on newsgroups if you post an SSCCE.
Without the source for the Student class in hand we've to guess
(correctly) why you cannot serialize the class.
BTW, there are other ways to write information to a file than
serialization.
what is the best way to do this? any suggestions?
| From: Robert Larsen |
Date: Monday, May 07, 2007
|
wrote in message:
what is the best way to do this? any suggestions?
That depends on a lot of things. An XML file I very easily read by
humans and
portable but often not very scalable. A database is very fast
and scalable. A binary file can be easy to work with (or very very hard).
What'd be the typical usage ? And how many records'd the file hold ?
| From: Lew |
Date: Tuesday, May 08, 2007
|
wrote in message:
wrote in message:
what is the best way to do this? any suggestions?
That depends on a lot of things. An XML file I very easily read by
humans and portable but often not very scalable. A database is very fast
and scalable. A binary file can be easy to work with (or very very hard).
What'd be the typical usage ? And how many records'd the file hold ?
There are gazillion ways to emit data. The simplest is to
open a file for
writing, say in a
variable 'wr' -
import JAVA.io.PrintWriter;
...
PrintWriter wr = new PrintWriter( someFileName );
...
wr.println( foo.getProperty().toString() );
Of course, 'toString()' in most cases won't give you what you want, but
it's a start.
Really you should just read the JAVAdocs on the JAVA.io package, and the tutorial:
<http://JAVA.sun.com/docs/books/tutorial/essential/io/index.html>
--
Lew
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