code: import java.io.*;
  
  public class FloatArray {
      public static void writeDat(String filename, double[] x, double[] y,
                                  int xprecision, int yprecision)
          throws IOException {
          assert x.length == y.length;
          PrintWriter out = new PrintWriter(filename);
          for (int i = 0; i < x.length; i++)
              out.printf("%."+xprecision+"g\t%."+yprecision+"g\n", x[i], y[i]);
          out.close();
      }
  
      public static void main(String[] args) {
          double[] x = {1, 2, 3, 1e11};
          double[] y = new double[x.length];
          for (int i = 0; i < x.length; i++)
              y[i] = Math.sqrt(x[i]);
  
          try {
              writeDat("sqrt.dat", x, y, 3, 5);
          } catch (IOException e) {
              System.err.println("writeDat: exception: "+e);
          }
  
          try {
              BufferedReader br = new BufferedReader(new FileReader("sqrt.dat"));
              String line;
              while ((line = br.readLine()) != null)
                  System.out.println(line);
          } catch (IOException e) { }
      }
  }
  