Question

I’m making an app that creates new files, there’s no problem when I name the files like this:

private String FILENAME = "myFilename";

but when I use a method to name the file, the compiler jumps straight to this line:

String lineSep = System.getProperty("line.separator");

then to my class declaration:

public class AddUser extends Activity

And the application crashes.

This is what the log file says:

12-03 16:26:12.814: E/AndroidRuntime(20307): FATAL EXCEPTION: main
12-03 16:26:12.814: E/AndroidRuntime(20307): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.app/com.myapp.app.ProfileSaved}: java.lang.NullPointerException
12-03 16:26:12.814: E/AndroidRuntime(20307):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
12-03 16:26:12.814: E/AndroidRuntime(20307):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
12-03 16:26:12.814: E/AndroidRuntime(20307):    at android.app.ActivityThread.access$600(ActivityThread.java:130)

This is my file naming method:

int firstArray;
int nextArray;  

private String fileNamer(){

    File dataDirectory = Environment.getDataDirectory();
    File fileDir = new File(dataDirectory, "data/com.myapp.app/files");

    String[] filenameArray = fileDir.list();

    Arrays.sort(filenameArray);

    if (filenameArray.length == 0){
        return "0";
    }

    if (filenameArray.length == 2500){
        return "too_many_items";
    }

    if (!filenameArray[0].equals("0")){
        return "0";
    }

    int arrayLength = filenameArray.length;
    int i;

    for(i=0; i<arrayLength-1;){

        firstArray = Integer.parseInt(filenameArray[i]);
        nextArray = Integer.parseInt(filenameArray[i+1]);

        if (firstArray+1 == nextArray){
            i++;
        }
    }
    return Integer.toString(nextArray+1);
}

The method seems to be working fine but I just can’t see why would it affect the rest of the program since all it does is to return a String?

Answer 1

Ok guys thanks for your input.

I believe I finally got it right. First of all the method indeed was buggy but that wasn’t really the issue, a good answer would’ve been something like:

“There IS a difference between a String and invoking a method that returns a String that is assigned to a variable, because in order to use the invoked String in another Class you’ll probably need to set the variable as static. That’s why the String is working and the ‘method invoked’ String not.”

About the bugs in the code just in case someone is ever interested, the if in

if (firstArray+1 == nextArray) 

needs the else in case there is an empty space between filenames, like 1, 3, 4 so the next file gets named 2.

The other bug was that I was comparing filenames as Strings so when I sorted them, they were sorted as 1, 10, 2, 3, 4, 5, 6, 7, 8, 9.

The solution I used was to add zeros to the beginning of the filenames like 0001, 0002, and so on.