Java read values from text file

Question

I am new to Java. I have one text file with below content.

`trace` -
structure(
 list(
  \"a\" = structure(c(0.748701,0.243802,0.227221,0.752231,0.261118,0.263         


        

Answer 1

You need to read the file line by line. It is done with a BufferedReader like this :

try {
    FileInputStream fstream = new FileInputStream("input.txt");
    BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
    String strLine;         
    int lineNumber = 0;
    double [] a = null;
    double [] b = null;
    // Read File Line By Line
    while ((strLine = br.readLine()) != null) {
        lineNumber++;
        if( lineNumber == 4 ){
            a = getDoubleArray(strLine);
        }else if( lineNumber == 5 ){
            b = getDoubleArray(strLine);
        }               
    }
    // Close the input stream
    in.close();
    //print the contents of a
    for(int i = 0; i < a.length; i++){
        System.out.println("a["+i+"] = "+a[i]);
    }           
} catch (Exception e) {// Catch exception if any
    System.err.println("Error: " + e.getMessage());
}

Assuming your "a" and"b" are on the fourth and fifth line of the file, you need to call a method when these lines are met that will return an array of double :

private static double[] getDoubleArray(String strLine) {
    double[] a;
    String[] split = strLine.split("[,)]"); //split the line at the ',' and ')' characters
    a = new double[split.length-1];
    for(int i = 0; i < a.length; i++){
        a[i] = Double.parseDouble(split[i+1]); //get the double value of the String
    }
    return a;
}

Hope this helps. I would still highly recommend reading the Java I/O and String tutorials.