Java使用外部文本文件中的数据

Question

I have a text file containing the first 1000 prime numbers and I have written a method to read the data from said text file.

I would like to know how to use the data from this file and apply it to another method.

Something along the lines of:

read data from file;
use first eight numbers and apply to this method;

Any help would be appreciated.

Answer 1

Read the file and store each number into an array or list. You can then get the numbers you need by using the index of the array.

Answer 2

Reading from file is simple, assuming you have one line per number -

BufferedReader br = new BufferedReader(new FileReader("<your-text-file>"));
String txtNum;
while((txtNum = br.readLine()) != null)
{
   //txtNum is the number read, use it however you need
   if (txtNum.length() > 8) {
      thisMethod(txtNum.substring(0, 8));
   }
}

Answer 3

Use Scanner to read the data from the file and store each line in an array (or ArrayList ) of int s. The get a subset of that array and pass it to a method supporting variable-length arguments (for example). Something like :

public static void main(String[] args) {
   ArrayList<Integer> primes = new ArrayList<Integer>();
   readPrimeData(new File("path/to/data"), primes);
   someMethod(primes.subList(0, 8).toArray(new Integer[0]));
}

static public boolean readPrimeData(File dataFile, ArrayList<Integer> data) {
   boolean err = false;
   try {
      Scanner scanner = new Scanner(dataFile);
      String line;
      while (scanner.hasNext()) {
         line = scanner.nextLine();
         try {
            data.add(Integer.parseInt(line));
         } catch (NumberFormatException e) {
            e.printStackTrace();
            err = true;
         }
      }
      scanner.close();
   } catch (FileNotFoundException e) {
      e.printStackTrace();
      err = true;
   }

   return err;
}


static public void someMethod(Integer...primes) {
   // primes is Integer[]
}

The method someMethod can also be called like

someMethod(1, 2, 3, 5, 7);

Answer 4

First, you have to know how you information is organized. For instance, you could have your 1000 first prime nunbers organized this way:

1
2
3
5
7...

Or this way:

1-2-3-5-7-11...

You can use the StringBuilder (or just a String) to keep the numbers of your file (assuming that your text is like the second way above). As the numbers are separated by a dash you could use a substring that can take the first 8 numbers to some method.

BufferedReader br = new BufferedReader(new FileReader("Prime Nunbers.txt"));
String num;
int count = 1;
while((num= br.readLine()) != null) {
      if( count <= 8 )     
        someMethod( num.subString(0, num.indexOf("-")) );
}

But if you have your numbers organized like the 1st way (one number per line) you could do something like this:

BufferedReader br = new BufferedReader(new FileReader("Prime Nunbers.txt"));
String num;
int count = 1;
while((num = br.readLine()) != null) {
        if( count <= 8 )
           someMethod( num );
        num = "";
}

If you want to use these first 8 numbers at once you can just read the file entirely and then use some substring depending the way these numbers are read.