save changes (permanently) in an arraylist?

Question

Is that possible? Like for example, a user added a new item/element into the arraylist (bufferedreader process) and surely, there would be changes happen. My question is that is it possible that even if a user makes changes into the arraylist many times, it would just be permanently there even if they close the program and open it agan, it's s till there.

Note: No usage of .txt

Sorry for asking such question but I am really curious about it. Thank you!

Once the application closes everything in the JVM goes bye-bye. You'll have to look into some persistence solution if you want to retain values across multiple application executions. — Ceiling Gecko, Mar 11 '14 at 11:12
By "No usage of .txt" do you mean "you can't store this in a file system"? — Jon Skeet, Mar 11 '14 at 11:13
ArrayList lives in memory. When your application is terminated, your arraylist is removed from memory. — Simon Mokhele, Mar 11 '14 at 11:16
if you want to retain some data even after closing your app then you need to persist data somewhere and that somewhere will be a file or database. now if you do not want .txt then you can serialize/deserialize your java objects — Sanjeev, Mar 11 '14 at 11:17

score 1 · Accepted Answer · answered Mar 11 '14 at 11:20

When the program stops, all memory it uses is released, including your ArrayList. There's no going around this except not to close the program. If you really need persistent data structures, you will have to write it to the hard drive somehow.

You asked not to use .txt. Well, that's all right, but you will have to create a file somewhere to store this data.

Luckily, ArrayList is serialisable. As long as the elements in it are serialisable, you can easily store it in a file with writeObject, as follows:

try {
    FileOutputStream fos = new FileOutputStream(filename);
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.writeObject(arraylist);
    oos.close();
} catch(Exception e) {
    e.printStackTrace();
}

And then you can recreate the ArrayList again with readObject.

ArrayList<Data> list;
try {
    FileInputStream fis = new FileInputStream(filename);
    ObjectInputStream ois = new ObjectInputStream(fis);
    list = (ArrayList<Data>) ois.readObject();
    ois.close();
} catch(Exception e) {
    e.printStackTrace();
}

Note that the objects you store in this ArrayList need to be serialisable as well. This means you have to make a writeObject and a readObject method for them if you made these classes.

score 0 · Answer 2 · answered Mar 11 '14 at 11:15

0

This is possible if your ArrayList is frequently
persisted either on the file system or in a database.
This is what you need to do.

answered Mar 11 '14 at 11:15

peter.petrov

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score 0 · Answer 3 · answered Mar 11 '14 at 11:21

The arraylist object you work with is just a variable of your program. While your program keeps a reference to this variable, but once you close the program the variable will disapear. If you want to keep the information inside of the variable you need to use a file or a database, you cannot store a java variable.

score 0 · Answer 4 · answered Mar 11 '14 at 11:25

If I understand you aren't allowed to use a text file to store your data in CSV format, maybe Serialization/Deserialization is what you, or your teacher ;-), want or wants you to do.

Read about ObjectOutputStream and ObjectInputStream and try your best. Here's a little example.

save changes (permanently) in an arraylist?

4 Answers4

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