Writing/Reading an ArrayList from a file.

Serialization is your friend:

import java.util.ArrayList;

import java.util.List;

import java.io.*;

class SerialTest {

public static void main(String[] argv) throws Exception {

List<String> list = new ArrayList<String>();

list.add("Caleb");

list.add("Ned");

list.add("Sally");

list.add("Fred");

File f = new File("test.fil");

FileOutputStream fos = new FileOutputStream(f);

ObjectOutputStream oos = new ObjectOutputStream(fos);

oos.writeObject(list);

oos.close();

System.out.println("Stored the list to a file.");

FileInputStream fis = new FileInputStream(f);

ObjectInputStream ois = new ObjectInputStream(fis);

List<String> newList = (ArrayList<String>)ois.readObject();

ois.close();

for( String s : newList) System.out.println(s);

}

}

Navy_Codera at 2007-7-29 11:38:25 >

I kind of having it going now...

here's the write.. when it writes to file.. it adds brackets.. like [ 1 1 1, 2 2 2 ] and etc.. is there anyway to remove them? when i read the file it brings the brackets in aswell..

public void actionPerformed(ActionEvent evt) {

try

{

JFileChooser chooser;

File file, directory;

int status;

chooser = new JFileChooser();

status = chooser.showSaveDialog(null);

if (status == JFileChooser.APPROVE_OPTION)

{

file= chooser.getSelectedFile();

directory = chooser.getCurrentDirectory();

PrintWriter pW = new PrintWriter(file);

pW.print(book);

pW.close();

}

else

{

JOptionPane.showMessageDialog(null, "Save File dialog canceled");

}

}

catch (Exception ex)

{

}

}

heres the read.. don't mind the variable names.. i stole it right from an example from the teacher..

private void openMenu() {

try

{

JFileChooser chooser;

File file, directory;

int status;

chooser = new JFileChooser();

status = chooser.showSaveDialog(null);

file= chooser.getSelectedFile();

directory = chooser.getCurrentDirectory();

FileReader fr = new FileReader(file);

BufferedReader br = new BufferedReader(fr);

String inRecord;

String inStoreNum, inStoreName, inStoreSales;

int storeCount = 0;

double totalSales = 0;

while ((inRecord = br.readLine()) != null)

{

StringTokenizer tokenizer = new StringTokenizer(inRecord);

inStoreNum = tokenizer.nextToken();

inStoreName = tokenizer.nextToken();

inStoreSales = tokenizer.nextToken();

System.out.println(inStoreNum + "" + inStoreName + " " + inStoreSales);

}

}

catch (Exception ex)

{

}

}

DenisKa at 2007-7-29 11:38:25 >

I tried but it doesn't work?

I tried putting it into my code but everytime i print the object it doesn't print the stuff in the arraylist, but rather this hashcode or something..

Keep in mind my teacher said we don't need to use serializable for this.. he didn't even get into serializable at all..

DenisKa at 2007-7-29 11:38:25 >

Well i looked at Navy's code and pretty much tried copying it, but when i printed the object it printed out some hashcode instead of the actual values.

DenisKa at 2007-7-29 11:38:25 >

> Well i looked at Navy's code and pretty much tried

> copying it,

Did you understand it before copying and using it?

> but when i printed the object it printed

> out some hashcode instead of the actual values.

Then you're either printing the wrong thing, or you didn't override toString somewhere that you need to.

jverda at 2007-7-29 11:38:25 >

> This code writes this to a file...

>

> sr java.util.ArrayListxa
I sizexp

Serialized data is not intended to be human readable. You read it back into your program with ObjectReader.readObject.

If you want human readable, use your own format or java.beans.XMLEncoder/Decoder.

jverda at 2007-7-29 11:38:25 >

So you're telling me that's right?mhm. ok, now i'll try reading.

DenisKa at 2007-7-29 11:38:25 >

When i try this, it doesn't print out anything..

File f = new File("input111.txt");

FileOutputStream fos = new FileOutputStream(f);

ObjectOutputStream oos = new ObjectOutputStream(fos);

oos.writeObject(book);

oos.close();

FileInputStream fis = new FileInputStream("input111.txt");

ObjectInputStream ois = new ObjectInputStream(fis);

List<String> newList = (ArrayList<String>)ois.readObject();

ois.close();

for( String s : newList) System.out.println(s);

DenisKa at 2007-7-29 11:38:30 >

I was expecting it to print out the stuff in ArrayList book. Because it wrote book to the file(or so i think) and the read is converting it back and being printed onto the terminal?

I have no idea what.. this does

List<String> newList = (ArrayList<String>)ois.readObject();

DenisKa at 2007-7-29 11:38:30 >

This is almost always a bad idea: catch (Exception ex) {}

You're saying, "If anything goes wrong, don't tell me about it. Just pretend everything is fine."

You should at the very least call ex.printStackTrace(). Even that's not proper exception handling, but at least you'll see what went wrong.

jverda at 2007-7-29 11:38:30 >

Well, there you have it.

You haven't made your BookMaintenance class implement Serializable, so of course nothing got written to the file.

jverda at 2007-7-29 11:38:30 >

> Ok, i made it implement Serializable, the file has

> something, but it's not readable

I already told you--serialized data is not meant to be human readable.

>, is there a way to

> get rid of the [ ] and the comma? and have it

Yes. Create your own format for writing and reading it.

jverda at 2007-7-29 11:38:30 >

writing to file

[ 1 1 1 , 2 2 2 ]

reading from file

[ 1 1 1 , 2 2 2 ]

Now if i only knew how to not have it print out the arraylist tostring and write properly to a file

File f = new File("input111.txt");

FileOutputStream fos = new FileOutputStream(f);

ObjectOutputStream oos = new ObjectOutputStream(fos);

System.out.println("writing to file");

System.out.println(book);

oos.writeObject(book);

oos.close();

FileInputStream fin = new FileInputStream("input111.txt");

ObjectInputStream ois = new ObjectInputStream(fin);

ArrayList readList = (ArrayList)ois.readObject();

ois.close();

System.out.println("reading from file");

System.out.println(readList);

DenisKa at 2007-7-29 11:38:30 >

> You seem to just be flobbering around, tossing off...

That's quite a turn of the phrase, Mr. J.

~

yawmarka at 2007-7-29 11:38:30 >

Stop.

Are you trying to write output to a file to be read by a human?

Are you trying to write output to a file to be read by a computer?

Both?

~

yawmarka at 2007-7-29 11:38:30 >

> Well i want it to write it to a file then when i open

> it, to read the contents of the file back into the

> GUI JTextFields.

Very well. Don't worry about what the output looks like in the file. Just read the file contents back in as an object(s) (i.e., de-serialize them, assuming you serialized them in the first place), and use the object's data to populate the text fields.

~

yawmarka at 2007-7-29 11:38:35 >

> Now if i only knew how to not have it print out the

> arraylist tostring and write properly to a file

It is writing properly.

Look, what are you trying to do? You want to write it to a file, and then have your program read it again later? Then you don't care what format it's in. Just test it by writing it, reading it back, and making sure you end up with the same objects you started with.

If you want the file to be readable by humans, then the simplest think is java.beans.XMLEncoder. Humans can read it and you can use XMLDecoder to read it back into your program.

If you don't like that format, then *you* decide what format you want, and *you* write the code to write it out and read it in in that format.

jverda at 2007-7-29 11:38:35 >

Okay, how about this. The arraylist is written to a file, now i want it to read and get to be displayed back into the JTextFields.. Thats it, i can careless how it looks in the file, how it's written, i only care about it working.

DenisKa at 2007-7-29 11:38:35 >

> Okay, how about this. The arraylist is written to a

> file, now i want it to read and get to be displayed

> back into the JTextFields..

Stop.

Two thigs.

Read it.

Display it in JTextField.

First do one. Then the oher. They are two completely unrelated things. Which one are you having problems with and exactly what probems are you having?

> Thats it, i can careless

> how it looks in the file,

That's right. You don't care how it looks in the file. But you've been making it soud like you do, or like it's not writing to the file correctly.

Please, for the love of god, be more detailed and precise.

jverda at 2007-7-29 11:38:35 >

> Sorry i thought the printing into the file mattered.

What matters is that the method that writes it writes out all the relevant information, and that the method that reads it knows how to interpret that information. writeObject and readObject have been around a long time, so you can assume that they work if you call them correctly (which you wern't doing originally, since you didn't implement Serializable).

What doesn't matter is what that format is, or whether you, as a human, can read it. If the file will only be written and read by software, not humans, then all tha matters is that the software can understand it.

> I thought when reading that i would have to use

> StringTokenizer

No. That's for tokenizing a String. For instance, if you read a text file and you want to break it up a certain way.

Readobject is already written to do whatever it needs to do to break apart the contents written by writeObject and assemble them into objects. This is known as encapsulation. You don't care *HOW* write/readObject work, only what end results they produce.

> I thought that if i

> read it and display it back into the gui that it

> would display the [1 as a value and etc.

Again, do NOT lump "reading and displaying" together.

You read it back. This gives you the same list you started with.

Now you want to display it. The display part doesn't know whether that list was read from a file or is the original that you started out with. It's just a list. The display part has to know how to display that list, but where it came from is irrelevant. This divide-and-conquer approach is of crucial importance when writing any software. Live it.

> Now, as for reading it, it is reading it. I dont need

> to use StringTokenizer at all right?

That depends. What format is it in? What's going to process it after reading it? If you wrote it with writeObject, then read it with readObject, and you'll end up with the same objects you started with. That's what write/readObject are for.

> I don't know how to get it back into the JTextFields

> though.

Okay. Make sure you understand that this is a completely separate issue from writing/reading the file.

You need to write a small method that just takes a list and displays it. Doesn't matter where the list comes from. Your initial testing of this method will simply use a hardcoded list that you create right there in the test program.

This method may need to in turn be broken out into smaller helper methods, but from the standpoint of "things I want to do," displaying a list is one "thing", so write a method whose job it is to display a list.

> Jverd, sorry for pissing you off, i don't mean to.

No, it's okay. I know there's a lot to take in at once and it can be hard for a newbie to separate the pieces out. I just get frustrated easily at communication misfires.

jverda at 2007-7-29 11:38:35 >

> I don't know how to display the list.

Okay. What have you tried and what problems did you have.

Post code. Just a tiny program with a main, a method to set up your text field or whatever, and a displayList method that takes your list as a parameter and display it. Main should call setupTextField (or whatever), create a hardcoded list, and then pass that list to displayList.

Do as much of that as you can and provide details about exactly what problems you're having. If there are error message, paste in the complete, exact message. If it works but doesn't behave as you want, describe your desired and observed behavior as precisely as you can.

When you post code, please use[code] and [/code] tags as described in Formatting tips on the message entry page. (http://forum.java.sun.com/help.jspa?sec=formatting) It makes it much easier to read.

jverda at 2007-7-29 11:38:35 >

I'm reading your post over and over and trying to even get a start going but it's not clicking, do you have any examples of this?

DenisKa at 2007-7-29 11:38:35 >

> I'm reading your post over and over and trying to

> even get a start going but it's not clicking, do you

> have any examples of this?

Okay, again, divide and conquer.

"I don't know how to display the list in a JTextField."

Do you know how to display *anything* in a JTextField? If not, google for a swing tutorial, or look at the links somebody posted a couple of posts ago.

Do you know how to write a main that calls two methods? If so, do that. Those methods can just do nothing but system.out.pritln their names.

Do you know how to write a little program where main calls two methods, and how to display some simple thing in a text field, but don't know how to display the *list*?

If so, then do as much as you can, and then look at this:

http://java.sun.com/docs/books/tutorial/collections/

Don't say you can't even start. You obviously can, as you have written *some* Java code.

One piece at a time.

Do you know how to dsplay

jverda at 2007-7-29 11:38:40 >

> I'm guessing something like this is displaying the

> lsit.

>

>Iterator iterator = book.iterator();

>while(iterator.hasNext())

>{

> System.out.println(iterator.next());

>

>

You're not listening.

You're getting ahead of yourself, and you're not breaking it down.

Displaying a list can be broken down into smaller parts:

1) for each item in the list, do something

2) display a single item.

Those two are completely independent of each other. Make sure you know how to do each one on its own. Then worry about combining them into "display the list."

Now, you mention System.out.println here, but previously you wanted to put something into a GUI. Println won't work for that.

BUT, if you want to test "doing something for each item in the list," println is a great way to test that.

jverda at 2007-7-29 11:38:40 >

> String text =

> list.toString().replaceAll("[\\[\\]]", "");

> this.textField.setText(text);

Ye gods, no.

1) I don't want to dump regex on him yet.

2) Relying on toString's format and munging that is a bad idea, IMHO.

jverda at 2007-7-29 11:38:40 >

> Here's an example of what jverd

> was asking for:

Denis,

Yes, what he said, mostly.

I disagree with part of yawmark's approach (though maybe he did that on purpose, to leave some work for you), and I think he put more in there than you initially should, but that's the idea.

Start with a tiny program--main plus two methods. Main first calls the method to set up the GUI. Then main calls the method to display the list.

If you know how to setup the GUI but not how to display the list, then the displayList method could just System.out.println("in display"). Or, if you know how to display one piece of text, but not the list, it could put "hello" in the text field.

The idea is to start with something small and simple that you know works, and to build on that piece by piece.

jverda at 2007-7-29 11:38:40 >

> > Ye gods, no.

>

> Just an example.

>

Yeah, I figured.

I just didn't want the OP to take it too literally.

> > 1) I don't want to dump regex on him yet.

>

> > 2) Relying on toString's format and munging that is

> a

> > bad idea, IMHO.

>

> Fair enough. I can't edit it now that you've replied,

> though.

MWUAH HA HA! My evil plan is working!

The repost is almost exactly what I'd been envisioning for the OP's first attempt though.

jverda at 2007-7-29 11:38:40 >

> > You're getting ahead of yourself, and you're not

> > breaking it down.

> >

> > Displaying a list can be broken down into smaller

> > parts:

> >

> > 1) for each item in the list, do something

> > 2) display a single item.

> >

> >

> Can't i just save each hasNext to a variable and then

> add it to the arraylist using a loop?

I don't know what you mean. However:

1) It's already in the ArrayList, no?

2) Try it with code. If you can't get it to work, post your code and specific questions/prolems.

> Mhm, i need to get away from the computer, i'm not

> event hinking straight anymore, i'll be back in a bit.

Okay. Learning when to step away is also very important. :-)

jverda at 2007-7-29 11:38:40 >

Ok i'm back.

DenisKa at 2007-7-29 11:38:40 >

Is there any other easier way to do this?

DenisKa at 2007-7-29 11:38:40 >

I don't know anything about GUIs, so I can't help you there. You might want to start a new thread in the swing forum if you have GUI specific quetsions.

As to whether something would work, the best way to answer that is to try it.

jverda at 2007-7-29 11:38:45 >

> Is there any other easier way to do this?

Unquestionably, yes.

~

yawmarka at 2007-7-29 11:38:45 >

This doesn't work. Help?

ArrayList book;

BookMaintenance bookMaint;

String fileName="dataFile.txt";

FileInputStream in = new FileInputStream(fileName);

ObjectInputStream s = new ObjectInputStream(in);

book = (ArrayList)s.readObject();

//Now loop the arraylist and put it into the windowpane

for(int i=0;i < book.size();i++){

bookMaint = book.get(i);

titleField = bookMaint.getTitle();

authorField = bookMaint.getAuthor();

publisherField = bookMaint.getPublisher();

}

DenisKa at 2007-7-29 11:38:45 >

> > This doesn't work. Help?

>

> "Doesn't work" is defined as causing a miniature

> donkey to flatulate in your direction every time you

> run your application. If this isn't your problem then

> please be a bit more specific (e.g., providing an

> error message, etc.). It's probably a type problem,

> but you haven't provided enough detail to make

> troubleshooting anything other than guesswork.

>

> ~

lol!

BookMaintenance.java:299: incompatible types

found: java.lang.Object

required: BookMaintenance

bookMaint = book.get(i);

^

BookMaintenance.java:300: incompatible types

found: java.lang.String

required: javax.swing.JTextField

titleField = bookMaint.getTitle();

^

BookMaintenance.java:301: incompatible types

found: java.lang.String

required: javax.swing.JTextField

authorField = bookMaint.getAuthor();

^

BookMaintenance.java:302: incompatible types

found: java.lang.String

required: javax.swing.JTextField

publisherField = bookMaint.getPublisher();

^

4 errors

Press any key to continue . . .

DenisKa at 2007-7-29 11:38:45 >

Did you read the error messages? They tell you exactly what's wrong. What exactly do you not understand about, say, "found : java.lang.Object required: BookMaintenance"?

jverda at 2007-7-29 11:38:45 >

I read the error msg, i know what it wants, but then again i don't? Does that make sense? :S

DenisKa at 2007-7-29 11:38:45 >