CODEWITHSUNDEEP
javaarraysarraylistfile-io
lord_sneed
lord_sneed

Reputation: 824

Values Not Being Read in Correctly From File

I am trying to read in x,y coordinates in from a file separated by a comma. However, the elements are not being added to the ArrayList properly. Where am I going wrong here?

ArrayList<Double> xpointArrayList = new ArrayList<Double>();
ArrayList<Double> ypointArrayList = new ArrayList<Double>();
try {
    BufferedReader input = new BufferedReader(new FileReader(args[0]));
    String line;
    while ((line = input.readLine()) != null) {
        line = input.readLine();
        String[] splitLine = line.split(",");

        double xValue = Double.parseDouble(splitLine[0]);
        double yValue = Double.parseDouble(splitLine[1]);

        xpointArrayList.add(xValue);
        ypointArrayList.add(yValue);
    }
    input.close();

    } catch (IOException e) {

    } catch (NullPointerException npe) {

    }

    double[] xpoints = new double[xpointArrayList.size()];
    for (int i = 0; i < xpoints.length; i++) {
        xpoints[i] = xpointArrayList.get(i);
    }
    double[] ypoints = new double[ypointArrayList.size()];
    for (int i = 0; i < ypoints.length; i++) {
        ypoints[i] = ypointArrayList.get(i);
    }

When I do the Array.toSring call on the xpoints and the ypoints array. It only has one number. For example in the file:

1,2
3,4
0,5

It only has 3.0 for the xpoints array and 4.0 for the ypoints array. Where is it going wrong?

Upvotes: 0

Views: 85

Answers (3)

Brian Roach
Brian Roach

Reputation: 76908

while ((line = input.readLine()) != null) {
    line = input.readLine();

You just read a line, discarded it, then read another line.

Rinse, repeat (since it's a loop).

In the future, you really should think about using the debugger. You can step through your code as it executes and see exactly what is going on. Learning to use it will be invaluable.

Edit To add: As GregHaskins points out the comments below, you also obscured the problem by catching the NullPointerException and not acting on it. On the second iteration of your loop, line would be null on the second call to readLine() because there was nothing left in the file. The call to split() then throws a NullPointerException which you catch ... then silently ignore.

Upvotes: 6

user1581106
user1581106

Reputation:

Your reading style is not right. You are calling the readLine() two times. One at the top and other just after entering the while() loop. This way u are not processing all the points. Some point coordinates are getting ignored. You should use.

while ((line = input.readLine()) != null) {

//line = input.readLine(); */Remove this */

*/your code */

}

Upvotes: 1

Matthew Diana
Matthew Diana

Reputation: 1106

You can also read input using the Scanner class. The following is a modified version of your code using the Scanner and File classes to read the File:

ArrayList<Double> xpointArrayList = new ArrayList<Double>();
ArrayList<Double> ypointArrayList = new ArrayList<Double>();
try {
    Scanner input = new Scanner(new File("testing.txt"));
    String line;
    while (input.hasNextLine()) {
        line = input.nextLine();
        String[] splitLine = line.split(",");

        double xValue = Double.parseDouble(splitLine[0]);
        double yValue = Double.parseDouble(splitLine[1]);

        xpointArrayList.add(xValue);
        ypointArrayList.add(yValue);
    }
    input.close();

    } catch (IOException e) {

    } catch (NullPointerException npe) {

    }

    double[] xpoints = new double[xpointArrayList.size()];
    for (int i = 0; i < xpoints.length; i++) {
        xpoints[i] = xpointArrayList.get(i);
    }
    double[] ypoints = new double[ypointArrayList.size()];
    for (int i = 0; i < ypoints.length; i++) {
        ypoints[i] = ypointArrayList.get(i);
    }

Upvotes: 1

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