piformula.java

一个一元曲线多项式数值演示例子

package numbercruncher.piutils;

import java.text.*;
import java.util.*;

/**
 * Utility class for programs that compute pi.
 */
public abstract class PiFormula {
  private static final DecimalFormat DECIMAL_FORMAT =
      new DecimalFormat("00");
  private static final SimpleDateFormat TIME_FORMAT =
      new SimpleDateFormat("HH:mm:ss.SSS");

  protected long startTime;
  protected long markTime;

  /**
   * Print the string containing the digits of pi.
   * @param piString the string containing the digits of pi
   */
  protected void printPi(String piString) {
    System.out.print("\npi = " + piString.substring(0, 2));

    int index = 2;
    int line = 0;
    int group = 0;
    int length = piString.length();

    // Loop for each group of 5 digits
    while (index + 5 < length) {
      System.out.print(piString.substring(index, index + 5) +
                       " ");
      index += 5;

      // End of line after 10 groups.
      if (++group == 10) {
        System.out.println();

        // Print a blank line after 10 lines.
        if (++line == 10) {
          System.out.println();
          line = 0;
        }

        System.out.print("       ");
        group = 0;
      }
    }

    // Print the last partial line.
    if (index < length) {
      System.out.println(piString.substring(index));
    }
  }

  /**
   * Return a timestamp string that contains the elapsed time period.
   * @param time the starting time of the period
   * @return the timestamp string
   */
  protected String timestamp(long time) {
    // Current time in hh:mm:ss.
    String tString = TIME_FORMAT.format(new Date());

    long elapsed = (System.currentTimeMillis() - time + 500)
        / 1000;
    long hours = elapsed / (60 * 60);
    long minutes = (elapsed % (60 * 60)) / 60;
    long seconds = elapsed % 60;

    // Current time followed by elapsed time as (hh:mm:ss).
    return tString + " (" + DECIMAL_FORMAT.format(hours) +
        ":" + DECIMAL_FORMAT.format(minutes) +
        ":" + DECIMAL_FORMAT.format(seconds) +
        ")";
  }
}