Source for java.lang.Float

   1: /* Float.java -- object wrapper for float
   2:    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2005
   3:    Free Software Foundation, Inc.
   4: 
   5: This file is part of GNU Classpath.
   6: 
   7: GNU Classpath is free software; you can redistribute it and/or modify
   8: it under the terms of the GNU General Public License as published by
   9: the Free Software Foundation; either version 2, or (at your option)
  10: any later version.
  11: 
  12: GNU Classpath is distributed in the hope that it will be useful, but
  13: WITHOUT ANY WARRANTY; without even the implied warranty of
  14: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15: General Public License for more details.
  16: 
  17: You should have received a copy of the GNU General Public License
  18: along with GNU Classpath; see the file COPYING.  If not, write to the
  19: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20: 02110-1301 USA.
  21: 
  22: Linking this library statically or dynamically with other modules is
  23: making a combined work based on this library.  Thus, the terms and
  24: conditions of the GNU General Public License cover the whole
  25: combination.
  26: 
  27: As a special exception, the copyright holders of this library give you
  28: permission to link this library with independent modules to produce an
  29: executable, regardless of the license terms of these independent
  30: modules, and to copy and distribute the resulting executable under
  31: terms of your choice, provided that you also meet, for each linked
  32: independent module, the terms and conditions of the license of that
  33: module.  An independent module is a module which is not derived from
  34: or based on this library.  If you modify this library, you may extend
  35: this exception to your version of the library, but you are not
  36: obligated to do so.  If you do not wish to do so, delete this
  37: exception statement from your version. */
  38: 
  39: 
  40: package java.lang;
  41: 
  42: /**
  43:  * Instances of class <code>Float</code> represent primitive
  44:  * <code>float</code> values.
  45:  *
  46:  * Additionally, this class provides various helper functions and variables
  47:  * related to floats.
  48:  *
  49:  * @author Paul Fisher
  50:  * @author Andrew Haley (aph@cygnus.com)
  51:  * @author Eric Blake (ebb9@email.byu.edu)
  52:  * @since 1.0
  53:  * @status updated to 1.4
  54:  */
  55: public final class Float extends Number implements Comparable
  56: {
  57:   /**
  58:    * Compatible with JDK 1.0+.
  59:    */
  60:   private static final long serialVersionUID = -2671257302660747028L;
  61: 
  62:   /**
  63:    * The maximum positive value a <code>double</code> may represent
  64:    * is 3.4028235e+38f.
  65:    */
  66:   public static final float MAX_VALUE = 3.4028235e+38f;
  67: 
  68:   /**
  69:    * The minimum positive value a <code>float</code> may represent
  70:    * is 1.4e-45.
  71:    */
  72:   public static final float MIN_VALUE = 1.4e-45f;
  73: 
  74:   /**
  75:    * The value of a float representation -1.0/0.0, negative infinity.
  76:    */
  77:   public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
  78: 
  79:   /**
  80:    * The value of a float representation 1.0/0.0, positive infinity.
  81:    */
  82:   public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
  83: 
  84:   /**
  85:    * All IEEE 754 values of NaN have the same value in Java.
  86:    */
  87:   public static final float NaN = 0.0f / 0.0f;
  88: 
  89:   /**
  90:    * The primitive type <code>float</code> is represented by this
  91:    * <code>Class</code> object.
  92:    * @since 1.1
  93:    */
  94:   public static final Class TYPE = VMClassLoader.getPrimitiveClass('F');
  95: 
  96:   /**
  97:    * The number of bits needed to represent a <code>float</code>.
  98:    * @since 1.5
  99:    */
 100:   public static final int SIZE = 32;
 101: 
 102:   /**
 103:    * The immutable value of this Float.
 104:    *
 105:    * @serial the wrapped float
 106:    */
 107:   private final float value;
 108: 
 109:   /**
 110:    * Create a <code>Float</code> from the primitive <code>float</code>
 111:    * specified.
 112:    *
 113:    * @param value the <code>float</code> argument
 114:    */
 115:   public Float(float value)
 116:   {
 117:     this.value = value;
 118:   }
 119: 
 120:   /**
 121:    * Create a <code>Float</code> from the primitive <code>double</code>
 122:    * specified.
 123:    *
 124:    * @param value the <code>double</code> argument
 125:    */
 126:   public Float(double value)
 127:   {
 128:     this.value = (float) value;
 129:   }
 130: 
 131:   /**
 132:    * Create a <code>Float</code> from the specified <code>String</code>.
 133:    * This method calls <code>Float.parseFloat()</code>.
 134:    *
 135:    * @param s the <code>String</code> to convert
 136:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 137:    *         <code>float</code>
 138:    * @throws NullPointerException if <code>s</code> is null
 139:    * @see #parseFloat(String)
 140:    */
 141:   public Float(String s)
 142:   {
 143:     value = parseFloat(s);
 144:   }
 145: 
 146:   /**
 147:    * Convert the <code>float</code> to a <code>String</code>.
 148:    * Floating-point string representation is fairly complex: here is a
 149:    * rundown of the possible values.  "<code>[-]</code>" indicates that a
 150:    * negative sign will be printed if the value (or exponent) is negative.
 151:    * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
 152:    * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
 153:    *
 154:    * <table border=1>
 155:    * <tr><th>Value of Float</th><th>String Representation</th></tr>
 156:    * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
 157:    * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
 158:    *     <td><code>[-]number.number</code></td></tr>
 159:    * <tr><td>Other numeric value</td>
 160:    *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
 161:    *          E[-]&lt;number&gt;</code></td></tr>
 162:    * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
 163:    * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
 164:    * </table>
 165:    *
 166:    * Yes, negative zero <em>is</em> a possible value.  Note that there is
 167:    * <em>always</em> a <code>.</code> and at least one digit printed after
 168:    * it: even if the number is 3, it will be printed as <code>3.0</code>.
 169:    * After the ".", all digits will be printed except trailing zeros. The
 170:    * result is rounded to the shortest decimal number which will parse back
 171:    * to the same float.
 172:    *
 173:    * <p>To create other output formats, use {@link java.text.NumberFormat}.
 174:    *
 175:    * @XXX specify where we are not in accord with the spec.
 176:    *
 177:    * @param f the <code>float</code> to convert
 178:    * @return the <code>String</code> representing the <code>float</code>
 179:    */
 180:   public static String toString(float f)
 181:   {
 182:     return VMDouble.toString(f, true);
 183:   }
 184: 
 185:   /**
 186:    * Creates a new <code>Float</code> object using the <code>String</code>.
 187:    *
 188:    * @param s the <code>String</code> to convert
 189:    * @return the new <code>Float</code>
 190:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 191:    *         <code>float</code>
 192:    * @throws NullPointerException if <code>s</code> is null
 193:    * @see #parseFloat(String)
 194:    */
 195:   public static Float valueOf(String s)
 196:   {
 197:     return new Float(parseFloat(s));
 198:   }
 199: 
 200:   /**
 201:    * Returns a <code>Float</code> object wrapping the value.
 202:    * In contrast to the <code>Float</code> constructor, this method
 203:    * may cache some values.  It is used by boxing conversion.
 204:    *
 205:    * @param val the value to wrap
 206:    * @return the <code>Float</code>
 207:    * 
 208:    * @since 1.5
 209:    */
 210:   public static Float valueOf(float val)
 211:   {
 212:     // We don't actually cache, but we could.
 213:     return new Float(val);
 214:   }
 215: 
 216:   /**
 217:    * Parse the specified <code>String</code> as a <code>float</code>. The
 218:    * extended BNF grammar is as follows:<br>
 219:    * <pre>
 220:    * <em>DecodableString</em>:
 221:    *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
 222:    *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
 223:    *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
 224:    *              [ <code>f</code> | <code>F</code> | <code>d</code>
 225:    *                | <code>D</code>] )
 226:    * <em>FloatingPoint</em>:
 227:    *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
 228:    *              [ <em>Exponent</em> ] )
 229:    *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
 230:    * <em>Exponent</em>:
 231:    *      ( ( <code>e</code> | <code>E</code> )
 232:    *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
 233:    * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
 234:    * </pre>
 235:    *
 236:    * <p>NaN and infinity are special cases, to allow parsing of the output
 237:    * of toString.  Otherwise, the result is determined by calculating
 238:    * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
 239:    * to the nearest float. Remember that many numbers cannot be precisely
 240:    * represented in floating point. In case of overflow, infinity is used,
 241:    * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
 242:    * this does not accept Unicode digits outside the ASCII range.
 243:    *
 244:    * <p>If an unexpected character is found in the <code>String</code>, a
 245:    * <code>NumberFormatException</code> will be thrown.  Leading and trailing
 246:    * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
 247:    * internal to the actual number are not allowed.
 248:    *
 249:    * <p>To parse numbers according to another format, consider using
 250:    * {@link java.text.NumberFormat}.
 251:    *
 252:    * @XXX specify where/how we are not in accord with the spec.
 253:    *
 254:    * @param str the <code>String</code> to convert
 255:    * @return the <code>float</code> value of <code>s</code>
 256:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 257:    *         <code>float</code>
 258:    * @throws NullPointerException if <code>s</code> is null
 259:    * @see #MIN_VALUE
 260:    * @see #MAX_VALUE
 261:    * @see #POSITIVE_INFINITY
 262:    * @see #NEGATIVE_INFINITY
 263:    * @since 1.2
 264:    */
 265:   public static float parseFloat(String str)
 266:   {
 267:     // XXX Rounding parseDouble() causes some errors greater than 1 ulp from
 268:     // the infinitely precise decimal.
 269:     return (float) Double.parseDouble(str);
 270:   }
 271: 
 272:   /**
 273:    * Return <code>true</code> if the <code>float</code> has the same
 274:    * value as <code>NaN</code>, otherwise return <code>false</code>.
 275:    *
 276:    * @param v the <code>float</code> to compare
 277:    * @return whether the argument is <code>NaN</code>
 278:    */
 279:   public static boolean isNaN(float v)
 280:   {
 281:     // This works since NaN != NaN is the only reflexive inequality
 282:     // comparison which returns true.
 283:     return v != v;
 284:   }
 285: 
 286:   /**
 287:    * Return <code>true</code> if the <code>float</code> has a value
 288:    * equal to either <code>NEGATIVE_INFINITY</code> or
 289:    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 290:    *
 291:    * @param v the <code>float</code> to compare
 292:    * @return whether the argument is (-/+) infinity
 293:    */
 294:   public static boolean isInfinite(float v)
 295:   {
 296:     return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
 297:   }
 298: 
 299:   /**
 300:    * Return <code>true</code> if the value of this <code>Float</code>
 301:    * is the same as <code>NaN</code>, otherwise return <code>false</code>.
 302:    *
 303:    * @return whether this <code>Float</code> is <code>NaN</code>
 304:    */
 305:   public boolean isNaN()
 306:   {
 307:     return isNaN(value);
 308:   }
 309: 
 310:   /**
 311:    * Return <code>true</code> if the value of this <code>Float</code>
 312:    * is the same as <code>NEGATIVE_INFINITY</code> or
 313:    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 314:    *
 315:    * @return whether this <code>Float</code> is (-/+) infinity
 316:    */
 317:   public boolean isInfinite()
 318:   {
 319:     return isInfinite(value);
 320:   }
 321: 
 322:   /**
 323:    * Convert the <code>float</code> value of this <code>Float</code>
 324:    * to a <code>String</code>.  This method calls
 325:    * <code>Float.toString(float)</code> to do its dirty work.
 326:    *
 327:    * @return the <code>String</code> representation
 328:    * @see #toString(float)
 329:    */
 330:   public String toString()
 331:   {
 332:     return toString(value);
 333:   }
 334: 
 335:   /**
 336:    * Return the value of this <code>Float</code> as a <code>byte</code>.
 337:    *
 338:    * @return the byte value
 339:    * @since 1.1
 340:    */
 341:   public byte byteValue()
 342:   {
 343:     return (byte) value;
 344:   }
 345: 
 346:   /**
 347:    * Return the value of this <code>Float</code> as a <code>short</code>.
 348:    *
 349:    * @return the short value
 350:    * @since 1.1
 351:    */
 352:   public short shortValue()
 353:   {
 354:     return (short) value;
 355:   }
 356: 
 357:   /**
 358:    * Return the value of this <code>Integer</code> as an <code>int</code>.
 359:    *
 360:    * @return the int value
 361:    */
 362:   public int intValue()
 363:   {
 364:     return (int) value;
 365:   }
 366: 
 367:   /**
 368:    * Return the value of this <code>Integer</code> as a <code>long</code>.
 369:    *
 370:    * @return the long value
 371:    */
 372:   public long longValue()
 373:   {
 374:     return (long) value;
 375:   }
 376: 
 377:   /**
 378:    * Return the value of this <code>Float</code>.
 379:    *
 380:    * @return the float value
 381:    */
 382:   public float floatValue()
 383:   {
 384:     return value;
 385:   }
 386: 
 387:   /**
 388:    * Return the value of this <code>Float</code> as a <code>double</code>
 389:    *
 390:    * @return the double value
 391:    */
 392:   public double doubleValue()
 393:   {
 394:     return value;
 395:   }
 396: 
 397:   /**
 398:    * Return a hashcode representing this Object. <code>Float</code>'s hash
 399:    * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
 400:    *
 401:    * @return this Object's hash code
 402:    * @see #floatToIntBits(float)
 403:    */
 404:   public int hashCode()
 405:   {
 406:     return floatToIntBits(value);
 407:   }
 408: 
 409:   /**
 410:    * Returns <code>true</code> if <code>obj</code> is an instance of
 411:    * <code>Float</code> and represents the same float value. Unlike comparing
 412:    * two floats with <code>==</code>, this treats two instances of
 413:    * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
 414:    * <code>-0.0</code> as unequal.
 415:    *
 416:    * <p>Note that <code>f1.equals(f2)</code> is identical to
 417:    * <code>floatToIntBits(f1.floatValue()) ==
 418:    *    floatToIntBits(f2.floatValue())</code>.
 419:    *
 420:    * @param obj the object to compare
 421:    * @return whether the objects are semantically equal
 422:    */
 423:   public boolean equals(Object obj)
 424:   {
 425:     if (! (obj instanceof Float))
 426:       return false;
 427: 
 428:     float f = ((Float) obj).value;
 429: 
 430:     // Avoid call to native method. However, some implementations, like gcj,
 431:     // are better off using floatToIntBits(value) == floatToIntBits(f).
 432:     // Check common case first, then check NaN and 0.
 433:     if (value == f)
 434:       return (value != 0) || (1 / value == 1 / f);
 435:     return isNaN(value) && isNaN(f);
 436:   }
 437: 
 438:   /**
 439:    * Convert the float to the IEEE 754 floating-point "single format" bit
 440:    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 441:    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 442:    * (masked by 0x007fffff) are the mantissa. This function collapses all
 443:    * versions of NaN to 0x7fc00000. The result of this function can be used
 444:    * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
 445:    * original <code>float</code> value.
 446:    *
 447:    * @param value the <code>float</code> to convert
 448:    * @return the bits of the <code>float</code>
 449:    * @see #intBitsToFloat(int)
 450:    */
 451:   public static int floatToIntBits(float value)
 452:   {
 453:     return VMFloat.floatToIntBits(value);
 454:   }
 455: 
 456:   /**
 457:    * Convert the float to the IEEE 754 floating-point "single format" bit
 458:    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 459:    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 460:    * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
 461:    * rather than collapsing to a canonical value. The result of this function
 462:    * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
 463:    * obtain the original <code>float</code> value.
 464:    *
 465:    * @param value the <code>float</code> to convert
 466:    * @return the bits of the <code>float</code>
 467:    * @see #intBitsToFloat(int)
 468:    */
 469:   public static int floatToRawIntBits(float value)
 470:   {
 471:     return VMFloat.floatToRawIntBits(value);
 472:   }
 473: 
 474:   /**
 475:    * Convert the argument in IEEE 754 floating-point "single format" bit
 476:    * layout to the corresponding float. Bit 31 (the most significant) is the
 477:    * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
 478:    * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
 479:    * NaN alone, so that you can recover the bit pattern with
 480:    * <code>Float.floatToRawIntBits(float)</code>.
 481:    *
 482:    * @param bits the bits to convert
 483:    * @return the <code>float</code> represented by the bits
 484:    * @see #floatToIntBits(float)
 485:    * @see #floatToRawIntBits(float)
 486:    */
 487:   public static float intBitsToFloat(int bits)
 488:   {
 489:     return VMFloat.intBitsToFloat(bits);
 490:   }
 491: 
 492:   /**
 493:    * Compare two Floats numerically by comparing their <code>float</code>
 494:    * values. The result is positive if the first is greater, negative if the
 495:    * second is greater, and 0 if the two are equal. However, this special
 496:    * cases NaN and signed zero as follows: NaN is considered greater than
 497:    * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
 498:    * zero is considered greater than negative zero.
 499:    *
 500:    * @param f the Float to compare
 501:    * @return the comparison
 502:    * @since 1.2
 503:    */
 504:   public int compareTo(Float f)
 505:   {
 506:     return compare(value, f.value);
 507:   }
 508: 
 509:   /**
 510:    * Behaves like <code>compareTo(Float)</code> unless the Object
 511:    * is not an <code>Float</code>.
 512:    *
 513:    * @param o the object to compare
 514:    * @return the comparison
 515:    * @throws ClassCastException if the argument is not a <code>Float</code>
 516:    * @see #compareTo(Float)
 517:    * @see Comparable
 518:    * @since 1.2
 519:    */
 520:   public int compareTo(Object o)
 521:   {
 522:     return compare(value, ((Float) o).value);
 523:   }
 524: 
 525:   /**
 526:    * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
 527:    * other words this compares two floats, special casing NaN and zero,
 528:    * without the overhead of objects.
 529:    *
 530:    * @param x the first float to compare
 531:    * @param y the second float to compare
 532:    * @return the comparison
 533:    * @since 1.4
 534:    */
 535:   public static int compare(float x, float y)
 536:   {
 537:     if (isNaN(x))
 538:       return isNaN(y) ? 0 : 1;
 539:     if (isNaN(y))
 540:       return -1;
 541:     // recall that 0.0 == -0.0, so we convert to infinities and try again
 542:     if (x == 0 && y == 0)
 543:       return (int) (1 / x - 1 / y);
 544:     if (x == y)
 545:       return 0;
 546: 
 547:     return x > y ? 1 : -1;
 548:   }
 549: }