Java：我如何从文件的每一行中读取4个数字。 并将它们放入变量中？

Question

The text file looks like this:

data,data,data,data
data,data,data,data

The data being numbers. 4 numbers separated by commas and about 2000 lines. However I only need to use 20 lines at a time. The starting line needs to be chosen by its number, and then it gets 19 additional lines.

This data needs to be put into variables (float) that are named uniquely so I can then do math on them. So it can be named like this:

DataOne1 DataOne2 DataOne3 DataOne4
DataTwo1 DataTwo2 DataTwo3 DataTwo4

This way I can then do math like DataTwo1 - DataOne3. These variables will of course just always be named the same but then I will be able to change the underlying data by picking new lines.

I'm sorry this is such a beginners question but I've been completely unable to put things together from different solutions to get my exact solution.

So my question is how do I do this?

Answer 1

1. You can read the entire line using Scanner method nextLine( ).

2. Then use split() method (I am assuming that the data is separated by( "," )commas), to get all the 4 data on the line.

eg:

String[] s = strLine.split(",");

3. Consider making an ArrayList of Float and then convert each item in the String[] array into a Float item in ArrayList , using Float.parseFloat()

ArrayList<Float> fArr = new ArrayList<Float>();
for (String temp : s){
    fArr.add(Float.parseFloat(temp));
}

4. Then do whatever calculation you need.

Answer 2

These are the steps you need to do in order to get what you want:

1. Open the file using a BufferedReader :

BufferedReader br = new BufferedReader(new FileReader(filename));

2. Get to the starting line:

for (int i = 0; i < startLine; i++) {
    line = br.readLine();
}

3. Process the 20 lines you need, storing the numbers in an ArrayList <Double>

for (int i = startLine; i < startLine + 20; i++) {
   line = br.readLine();

   // Split the lines using comma as delimiter
   String[] numberStrings = line.split(",");
   ArrayList<Double> numbers= new ArrayList<Double>();

   for(String numberString : numberStrings) {
       Double number = Double.valueOf(numberString);
       numbers.add(number);
   }
   // Do calculations with them
}

Answer 3

Here is the code. For each line, I ve stored the values in array. So your DataOne1 will be in cols0[0], DataTwo1 will be in cols0[1], DataTwo1 will be in cols1[0] and DataTwo2 will be in cols1[1] and so-on. You can very well use the two-d array for this purpose, but to keep it simple I ve choosen this approach.

 try {
        BufferedReader br = new BufferedReader(new FileReader("fileName"));
        String line;
        float[] col0 = new float[20];
        float[] col1 = new float[20];
        float[] col2 = new float[20];
        float[] col3 = new float[20];
        for (int i = 0; i < 20; i++) {
            while((line = br.readLine()) != null) {
                // Since you told comma as separator.
                String[] cols = line.split(","); 
                col0[i] = Float.valueOf(cols[0]);
                col1[i] = Float.valueOf(cols[1]);
                col2[i] = Float.valueOf(cols[2]);
                col3[i] = Float.valueOf(cols[3]);
            }
            // Do something - your math.
        }
        br.close();
    }
    catch (FileNotFoundException e1) {
        e1.printStackTrace();
    }
    catch (IOException e) {
        e.printStackTrace();
    }