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 immutable value of this Float.
  98:    *
  99:    * @serial the wrapped float
 100:    */
 101:   private final float value;
 102: 
 103:   /**
 104:    * Create a <code>Float</code> from the primitive <code>float</code>
 105:    * specified.
 106:    *
 107:    * @param value the <code>float</code> argument
 108:    */
 109:   public Float(float value)
 110:   {
 111:     this.value = value;
 112:   }
 113: 
 114:   /**
 115:    * Create a <code>Float</code> from the primitive <code>double</code>
 116:    * specified.
 117:    *
 118:    * @param value the <code>double</code> argument
 119:    */
 120:   public Float(double value)
 121:   {
 122:     this.value = (float) value;
 123:   }
 124: 
 125:   /**
 126:    * Create a <code>Float</code> from the specified <code>String</code>.
 127:    * This method calls <code>Float.parseFloat()</code>.
 128:    *
 129:    * @param s the <code>String</code> to convert
 130:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 131:    *         <code>float</code>
 132:    * @throws NullPointerException if <code>s</code> is null
 133:    * @see #parseFloat(String)
 134:    */
 135:   public Float(String s)
 136:   {
 137:     value = parseFloat(s);
 138:   }
 139: 
 140:   /**
 141:    * Convert the <code>float</code> to a <code>String</code>.
 142:    * Floating-point string representation is fairly complex: here is a
 143:    * rundown of the possible values.  "<code>[-]</code>" indicates that a
 144:    * negative sign will be printed if the value (or exponent) is negative.
 145:    * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
 146:    * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
 147:    *
 148:    * <table border=1>
 149:    * <tr><th>Value of Float</th><th>String Representation</th></tr>
 150:    * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
 151:    * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
 152:    *     <td><code>[-]number.number</code></td></tr>
 153:    * <tr><td>Other numeric value</td>
 154:    *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
 155:    *          E[-]&lt;number&gt;</code></td></tr>
 156:    * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
 157:    * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
 158:    * </table>
 159:    *
 160:    * Yes, negative zero <em>is</em> a possible value.  Note that there is
 161:    * <em>always</em> a <code>.</code> and at least one digit printed after
 162:    * it: even if the number is 3, it will be printed as <code>3.0</code>.
 163:    * After the ".", all digits will be printed except trailing zeros. The
 164:    * result is rounded to the shortest decimal number which will parse back
 165:    * to the same float.
 166:    *
 167:    * <p>To create other output formats, use {@link java.text.NumberFormat}.
 168:    *
 169:    * @XXX specify where we are not in accord with the spec.
 170:    *
 171:    * @param f the <code>float</code> to convert
 172:    * @return the <code>String</code> representing the <code>float</code>
 173:    */
 174:   public static String toString(float f)
 175:   {
 176:     return VMDouble.toString(f, true);
 177:   }
 178: 
 179:   /**
 180:    * Creates a new <code>Float</code> object using the <code>String</code>.
 181:    *
 182:    * @param s the <code>String</code> to convert
 183:    * @return the new <code>Float</code>
 184:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 185:    *         <code>float</code>
 186:    * @throws NullPointerException if <code>s</code> is null
 187:    * @see #parseFloat(String)
 188:    */
 189:   public static Float valueOf(String s)
 190:   {
 191:     return new Float(parseFloat(s));
 192:   }
 193: 
 194:   /**
 195:    * Parse the specified <code>String</code> as a <code>float</code>. The
 196:    * extended BNF grammar is as follows:<br>
 197:    * <pre>
 198:    * <em>DecodableString</em>:
 199:    *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
 200:    *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
 201:    *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
 202:    *              [ <code>f</code> | <code>F</code> | <code>d</code>
 203:    *                | <code>D</code>] )
 204:    * <em>FloatingPoint</em>:
 205:    *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
 206:    *              [ <em>Exponent</em> ] )
 207:    *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
 208:    * <em>Exponent</em>:
 209:    *      ( ( <code>e</code> | <code>E</code> )
 210:    *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
 211:    * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
 212:    * </pre>
 213:    *
 214:    * <p>NaN and infinity are special cases, to allow parsing of the output
 215:    * of toString.  Otherwise, the result is determined by calculating
 216:    * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
 217:    * to the nearest float. Remember that many numbers cannot be precisely
 218:    * represented in floating point. In case of overflow, infinity is used,
 219:    * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
 220:    * this does not accept Unicode digits outside the ASCII range.
 221:    *
 222:    * <p>If an unexpected character is found in the <code>String</code>, a
 223:    * <code>NumberFormatException</code> will be thrown.  Leading and trailing
 224:    * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
 225:    * internal to the actual number are not allowed.
 226:    *
 227:    * <p>To parse numbers according to another format, consider using
 228:    * {@link java.text.NumberFormat}.
 229:    *
 230:    * @XXX specify where/how we are not in accord with the spec.
 231:    *
 232:    * @param str the <code>String</code> to convert
 233:    * @return the <code>float</code> value of <code>s</code>
 234:    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 235:    *         <code>float</code>
 236:    * @throws NullPointerException if <code>s</code> is null
 237:    * @see #MIN_VALUE
 238:    * @see #MAX_VALUE
 239:    * @see #POSITIVE_INFINITY
 240:    * @see #NEGATIVE_INFINITY
 241:    * @since 1.2
 242:    */
 243:   public static float parseFloat(String str)
 244:   {
 245:     // XXX Rounding parseDouble() causes some errors greater than 1 ulp from
 246:     // the infinitely precise decimal.
 247:     return (float) Double.parseDouble(str);
 248:   }
 249: 
 250:   /**
 251:    * Return <code>true</code> if the <code>float</code> has the same
 252:    * value as <code>NaN</code>, otherwise return <code>false</code>.
 253:    *
 254:    * @param v the <code>float</code> to compare
 255:    * @return whether the argument is <code>NaN</code>
 256:    */
 257:   public static boolean isNaN(float v)
 258:   {
 259:     // This works since NaN != NaN is the only reflexive inequality
 260:     // comparison which returns true.
 261:     return v != v;
 262:   }
 263: 
 264:   /**
 265:    * Return <code>true</code> if the <code>float</code> has a value
 266:    * equal to either <code>NEGATIVE_INFINITY</code> or
 267:    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 268:    *
 269:    * @param v the <code>float</code> to compare
 270:    * @return whether the argument is (-/+) infinity
 271:    */
 272:   public static boolean isInfinite(float v)
 273:   {
 274:     return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
 275:   }
 276: 
 277:   /**
 278:    * Return <code>true</code> if the value of this <code>Float</code>
 279:    * is the same as <code>NaN</code>, otherwise return <code>false</code>.
 280:    *
 281:    * @return whether this <code>Float</code> is <code>NaN</code>
 282:    */
 283:   public boolean isNaN()
 284:   {
 285:     return isNaN(value);
 286:   }
 287: 
 288:   /**
 289:    * Return <code>true</code> if the value of this <code>Float</code>
 290:    * is the same as <code>NEGATIVE_INFINITY</code> or
 291:    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 292:    *
 293:    * @return whether this <code>Float</code> is (-/+) infinity
 294:    */
 295:   public boolean isInfinite()
 296:   {
 297:     return isInfinite(value);
 298:   }
 299: 
 300:   /**
 301:    * Convert the <code>float</code> value of this <code>Float</code>
 302:    * to a <code>String</code>.  This method calls
 303:    * <code>Float.toString(float)</code> to do its dirty work.
 304:    *
 305:    * @return the <code>String</code> representation
 306:    * @see #toString(float)
 307:    */
 308:   public String toString()
 309:   {
 310:     return toString(value);
 311:   }
 312: 
 313:   /**
 314:    * Return the value of this <code>Float</code> as a <code>byte</code>.
 315:    *
 316:    * @return the byte value
 317:    * @since 1.1
 318:    */
 319:   public byte byteValue()
 320:   {
 321:     return (byte) value;
 322:   }
 323: 
 324:   /**
 325:    * Return the value of this <code>Float</code> as a <code>short</code>.
 326:    *
 327:    * @return the short value
 328:    * @since 1.1
 329:    */
 330:   public short shortValue()
 331:   {
 332:     return (short) value;
 333:   }
 334: 
 335:   /**
 336:    * Return the value of this <code>Integer</code> as an <code>int</code>.
 337:    *
 338:    * @return the int value
 339:    */
 340:   public int intValue()
 341:   {
 342:     return (int) value;
 343:   }
 344: 
 345:   /**
 346:    * Return the value of this <code>Integer</code> as a <code>long</code>.
 347:    *
 348:    * @return the long value
 349:    */
 350:   public long longValue()
 351:   {
 352:     return (long) value;
 353:   }
 354: 
 355:   /**
 356:    * Return the value of this <code>Float</code>.
 357:    *
 358:    * @return the float value
 359:    */
 360:   public float floatValue()
 361:   {
 362:     return value;
 363:   }
 364: 
 365:   /**
 366:    * Return the value of this <code>Float</code> as a <code>double</code>
 367:    *
 368:    * @return the double value
 369:    */
 370:   public double doubleValue()
 371:   {
 372:     return value;
 373:   }
 374: 
 375:   /**
 376:    * Return a hashcode representing this Object. <code>Float</code>'s hash
 377:    * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
 378:    *
 379:    * @return this Object's hash code
 380:    * @see #floatToIntBits(float)
 381:    */
 382:   public int hashCode()
 383:   {
 384:     return floatToIntBits(value);
 385:   }
 386: 
 387:   /**
 388:    * Returns <code>true</code> if <code>obj</code> is an instance of
 389:    * <code>Float</code> and represents the same float value. Unlike comparing
 390:    * two floats with <code>==</code>, this treats two instances of
 391:    * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
 392:    * <code>-0.0</code> as unequal.
 393:    *
 394:    * <p>Note that <code>f1.equals(f2)</code> is identical to
 395:    * <code>floatToIntBits(f1.floatValue()) ==
 396:    *    floatToIntBits(f2.floatValue())</code>.
 397:    *
 398:    * @param obj the object to compare
 399:    * @return whether the objects are semantically equal
 400:    */
 401:   public boolean equals(Object obj)
 402:   {
 403:     if (! (obj instanceof Float))
 404:       return false;
 405: 
 406:     float f = ((Float) obj).value;
 407: 
 408:     // Avoid call to native method. However, some implementations, like gcj,
 409:     // are better off using floatToIntBits(value) == floatToIntBits(f).
 410:     // Check common case first, then check NaN and 0.
 411:     if (value == f)
 412:       return (value != 0) || (1 / value == 1 / f);
 413:     return isNaN(value) && isNaN(f);
 414:   }
 415: 
 416:   /**
 417:    * Convert the float to the IEEE 754 floating-point "single format" bit
 418:    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 419:    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 420:    * (masked by 0x007fffff) are the mantissa. This function collapses all
 421:    * versions of NaN to 0x7fc00000. The result of this function can be used
 422:    * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
 423:    * original <code>float</code> value.
 424:    *
 425:    * @param value the <code>float</code> to convert
 426:    * @return the bits of the <code>float</code>
 427:    * @see #intBitsToFloat(int)
 428:    */
 429:   public static int floatToIntBits(float value)
 430:   {
 431:     return VMFloat.floatToIntBits(value);
 432:   }
 433: 
 434:   /**
 435:    * Convert the float to the IEEE 754 floating-point "single format" bit
 436:    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 437:    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 438:    * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
 439:    * rather than collapsing to a canonical value. The result of this function
 440:    * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
 441:    * obtain the original <code>float</code> value.
 442:    *
 443:    * @param value the <code>float</code> to convert
 444:    * @return the bits of the <code>float</code>
 445:    * @see #intBitsToFloat(int)
 446:    */
 447:   public static int floatToRawIntBits(float value)
 448:   {
 449:     return VMFloat.floatToRawIntBits(value);
 450:   }
 451: 
 452:   /**
 453:    * Convert the argument in IEEE 754 floating-point "single format" bit
 454:    * layout to the corresponding float. Bit 31 (the most significant) is the
 455:    * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
 456:    * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
 457:    * NaN alone, so that you can recover the bit pattern with
 458:    * <code>Float.floatToRawIntBits(float)</code>.
 459:    *
 460:    * @param bits the bits to convert
 461:    * @return the <code>float</code> represented by the bits
 462:    * @see #floatToIntBits(float)
 463:    * @see #floatToRawIntBits(float)
 464:    */
 465:   public static float intBitsToFloat(int bits)
 466:   {
 467:     return VMFloat.intBitsToFloat(bits);
 468:   }
 469: 
 470:   /**
 471:    * Compare two Floats numerically by comparing their <code>float</code>
 472:    * values. The result is positive if the first is greater, negative if the
 473:    * second is greater, and 0 if the two are equal. However, this special
 474:    * cases NaN and signed zero as follows: NaN is considered greater than
 475:    * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
 476:    * zero is considered greater than negative zero.
 477:    *
 478:    * @param f the Float to compare
 479:    * @return the comparison
 480:    * @since 1.2
 481:    */
 482:   public int compareTo(Float f)
 483:   {
 484:     return compare(value, f.value);
 485:   }
 486: 
 487:   /**
 488:    * Behaves like <code>compareTo(Float)</code> unless the Object
 489:    * is not an <code>Float</code>.
 490:    *
 491:    * @param o the object to compare
 492:    * @return the comparison
 493:    * @throws ClassCastException if the argument is not a <code>Float</code>
 494:    * @see #compareTo(Float)
 495:    * @see Comparable
 496:    * @since 1.2
 497:    */
 498:   public int compareTo(Object o)
 499:   {
 500:     return compare(value, ((Float) o).value);
 501:   }
 502: 
 503:   /**
 504:    * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
 505:    * other words this compares two floats, special casing NaN and zero,
 506:    * without the overhead of objects.
 507:    *
 508:    * @param x the first float to compare
 509:    * @param y the second float to compare
 510:    * @return the comparison
 511:    * @since 1.4
 512:    */
 513:   public static int compare(float x, float y)
 514:   {
 515:     if (isNaN(x))
 516:       return isNaN(y) ? 0 : 1;
 517:     if (isNaN(y))
 518:       return -1;
 519:     // recall that 0.0 == -0.0, so we convert to infinities and try again
 520:     if (x == 0 && y == 0)
 521:       return (int) (1 / x - 1 / y);
 522:     if (x == y)
 523:       return 0;
 524: 
 525:     return x > y ? 1 : -1;
 526:   }
 527: }