Storing integers and arrays in a file and reading them

Question

I want to store some integers and arrays into a file so i can let my program read and use them, but I have no idea how to do this. I know that I can read single integers with a Scanner and save them to an array by iteration, but I would like to have a file like

Number=5;
Array={1, 2, 3, 4, 5};

And my program should assign the numbers to it's variables automatically, like

int Number = file.get(Number);
int[] Array = file.get(Array);

Is there some way to accomplish this?

Thank you in advance

There are plenty ways to do it, depending on how the data is stored in the file: binary data, plain text, from a specific format like XML or JSON... — Luiggi Mendoza, Jan 05 '15 at 20:10
Regardless of what you use, you will have to write some part of the function `file.get` yourself. The closest thing to "automatic" you will get is probably JSON or some binary encoding. — merlin2011, Jan 05 '15 at 20:12
Yes, I have already read about JSON, XML and Property files, but I did not really understand how to do what I want with them. — vicco, Jan 05 '15 at 20:14
Start with Java Properties, write several test programs as simple as possible, each one doing the single thing. Repeat until you have better understanding. There's no other way. — Victor Sorokin, Jan 05 '15 at 20:16
possible duplicate of [How to Create JSON Array in Java](http://stackoverflow.com/questions/7976643/how-to-create-json-array-in-java) — merlin2011, Jan 05 '15 at 20:20

Santiago Benoit · Accepted Answer · 2015-01-05T21:00:58.473

0

The easiest way to do this is by using serialization. To store your information in a file, use a FileOutputStream and an ObjectOutputStream (from the java.io package), like this:

File saveFile = new File("filename.sav");
try {
    FileOutputStream fileOut = new FileOutputStream(saveFile);
    try (ObjectOutputStream objOut = new ObjectOutputStream(fileOut)) {
        objOut.writeObject(number); // you should use lower case for variable names
        objOut.writeObject(array);
    }
} catch (IOException e) {
}

This will store your information in a binary file named "filename.sav". To get your integer and array from that file, use a FileInputStream and an ObjectInputStream and cast the retrieved objects to the desired type in the order they were stored in:

try {
    FileInputStream fileIn = new FileInputStream("filename.sav");
    try (ObjectInputStream objIn = new ObjectInputStream(fileIn)) {
        int number = (int) objIn.readObject();
        int[] array = (int[]) objIn.readObject();
    }
} catch (IOException | ClassNotFoundException e) {
}

This will also work for any serializable object (an object that implements Serializable).

edited Jan 05 '15 at 21:00

answered Jan 05 '15 at 20:51

Santiago Benoit

994
1
8
22

Thank you, that should do it. Is there a way to write the file by hand? – vicco Jan 05 '15 at 21:04
By "by hand", do you mean storing the information to a plain text file? – Santiago Benoit Jan 05 '15 at 21:08
Yes, I would like to write it down in an editor, my program does not to write the file. – vicco Jan 05 '15 at 21:30
If you want to write to a text file, do the same thing except don't use an `ObjectOutputStream`. Instead, just write your strings directly from the `FileOutputStream`. – Santiago Benoit Jan 06 '15 at 21:34

Storing integers and arrays in a file and reading them

1 Answers1