YailNumberToString.java

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// -*- mode: java; c-basic-offset: 2; -*-
// Copyright 2009-2011 Google, All Rights reserved
// Copyright 2011-2012 MIT, All rights reserved
// Released under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0
 
package com.google.appinventor.components.runtime.util;
 
import android.util.Log;
 
 
import java.text.*;
import java.util.Locale;
 
public final class YailNumberToString {
 
  static final String LOG_TAG = "YailNumberToString";
 
  // format magnitudes larger than BIGBOUND in scientific notation
  private static final double BIGBOUND = 1.e6;
  // format magnitudes smaller than SMALLBOUND in scientific notation
  private static final double SMALLBOUND = 1.e-6;
 
 
  // TODO(halabelson): The Java documentation warns that formatters are
  // not thread-safe.  Is there any way that this can bite us?
  // format for decimal notation
  private static final String decPattern = "#####0.0####";
  // format for scientific notation
  private static final String sciPattern = "0.####E0";
 
  // TODO(hal): We are making the decimal separator be a period, regardless of
  // the locale of the phone.   We need to think about how to allow comma as decimal separator,
  // which will require updating number parsing and other places that transform numbers to strings,
  // such as FormatAsDecimal
 
  static Locale locale = Locale.US;
  static DecimalFormatSymbols symbols = new DecimalFormatSymbols(locale);
 
  static DecimalFormat decimalFormat = new DecimalFormat(decPattern, symbols);
  static DecimalFormat sciFormat = new DecimalFormat(sciPattern, symbols);
 
 
  // TODO(halabelson): DecimalFormat scientific notation apparently does not provide a
  // way to specify the maximum number of digits in the mantissa. One consequence is that this
  // formatting method, when given floats of very large magnitude, will produce too many
  // places in the mantissa.  Consider post-processing the result of
  // DecimalFormat to remove these extra digits.
 
  // This implementation assumes that Kawa inexact numbers are passed to this routine
  // as doubles.
  public static String format(double number) {
    // Handle positive and negative infinities (which are "round" and therefore coerce to long)
    if (Double.isInfinite(number)) {
      if (number < 0.0) {
        return "-infinity";
      } else {
        return "+infinity";
      }
    }
    // We will print integer values without a decimal point.
    if (number == Math.rint(number)) {
      return String.valueOf((long) number);
    } else {
      double mag = Math.abs(number);
      if (mag < BIGBOUND && mag > SMALLBOUND) {
        return decimalFormat.format(number);
      } else {
        return sciFormat.format(number);
      }
    }
  }
}