Data operation in memory

Question

I know it is always better to operate data in memory instead of file. Currently, I am putting all incoming data in a static ArrayList, and when that ArrayList has more than 80 entries, my program will save the contents of this ArrayList to a file and clear up this array for the next wave of coming data.

I wonder if it's better (or worse) to use Vector instead of ArrayList. If there is difference, which is better/worse? And in which case?

Here is my relevant code:

public class Exchange () {
    private static ArrayList<String> datain = new ArrayList<String> ();
    public static void addData(String s) {
        datain.add(s);
    }

    public static boolean checkSize() {
        if (datain.size() >= 80)
            return true;
        else
            return false;
    }

    public static void writeData() throws FileNotFoundException {
        PrintWriter pw = new PrintWriter(new File ("myfile.txt"));
        for (int i = 0; i < datain.size(); i++) {
            pw.println(datain.get(i);
        }
        pw.close();
    }

    public static void clear() {
        datain = new ArrayList<String>();
    }
}

P.S. This approach currently works fine, I am just wondering whether using vector will be better for this case. Also, if you see any bad design, feel free to point it out. Thanks!

Note: your `checkSize()` method could simply do `return datain.size() >= 80;`. Try to avoid `if(condition) return true; else return false;` — Alexis C., May 02 '14 at 18:34
You can use `Exchanger` for this sort of thing. Writing 80 lines at a time or one line 80x will take the same amount of time. — Peter Lawrey, May 02 '14 at 18:36
I also fail to understand your logic: each time writeData() is called, it replaces the entries currently in the file by the one in the list. — JB Nizet, May 02 '14 at 18:37
If you are happy to discard your lines every so often, could you just avoid writing anything. — Peter Lawrey, May 02 '14 at 18:38
@Zouzou: Is there any particular reason why I should avoid using if/else condition in this? — , May 02 '14 at 18:39
@JBNizet Sorry, I have another class taking care of backing up the "myfile.txt". I am thinking of using this class for auto-backup purpose. — , May 02 '14 at 18:41
@BallroomProgrammer if your condition is evaluated to true, you return true else you return false. So just return the value of the condition direclty. — Alexis C., May 02 '14 at 18:41
Why wouldn't you use a `String[]` if you know the exact capacity...? — 2rs2ts, May 02 '14 at 20:00

score 1 · Accepted Answer · answered May 02 '14 at 18:35

1

In the vast majority of cases, using ArrayList will suffice. The primary difference is that Vector is thread-safe, whilst ArrayList is not, but seeing as you aren't working with multiple threads, there is no reason to prefer Vector over ArrayList in your code

answered May 02 '14 at 18:35

awksp

11,764
4
37
44

Vector is also a legacy class which was replaced by ArrayList in Java 1.2 (1998) – Peter Lawrey May 02 '14 at 18:36
1

Unless you want a synchronized implementation, but even then you're almost always better off doing your synchronization in a different way – awksp May 02 '14 at 18:37
2

@user3580294: if you want a synchronized implementation, similar to Vector, you just need `Collections.synchronizedList(new ArrayList())` – JB Nizet May 02 '14 at 18:38
1

Which is why I said you're almost always better off doing your synchronization in a different way – awksp May 02 '14 at 18:39

score 0 · Answer 2 · answered May 02 '14 at 18:43

This is how I would do it, unless I know there is a performance issue. Most of the cost is in the opening and closing of the file, so I would avoid doing that. I would also assume that appending is what you want.

public enum Logging {
    ; // no instances
    public static final String FILE_NAME = "myfile.txt";
    private static final PrintWriter pw;

    static {
        try {
            pw = new PrintWriter(new FileWriter(FILE_NAME, true));
        } catch (IOException ioe) {
            throw new AssertionError(ioe);
        }
    }

    public static void addData(String s) {
        pw.println(s);
    }
}

Data operation in memory

2 Answers2