libjava/java/lang/Float.java

   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., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 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 Double.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   // GCJ LOCAL: We diverge from Classpath for efficiency.
 430   public static native int floatToIntBits(float value);
 431   // END GCJ LOCAL
 432
 433   /**
 434    * Convert the float to the IEEE 754 floating-point "single format" bit
 435    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 436    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 437    * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
 438    * rather than collapsing to a canonical value. The result of this function
 439    * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
 440    * obtain the original <code>float</code> value.
 441    *
 442    * @param value the <code>float</code> to convert
 443    * @return the bits of the <code>float</code>
 444    * @see #intBitsToFloat(int)
 445    */
 446   // GCJ LOCAL: We diverge from Classpath for efficiency.
 447   public static native int floatToRawIntBits(float value);
 448   // END GCJ LOCAL
 449
 450   /**
 451    * Convert the argument in IEEE 754 floating-point "single format" bit
 452    * layout to the corresponding float. Bit 31 (the most significant) is the
 453    * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
 454    * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
 455    * NaN alone, so that you can recover the bit pattern with
 456    * <code>Float.floatToRawIntBits(float)</code>.
 457    *
 458    * @param bits the bits to convert
 459    * @return the <code>float</code> represented by the bits
 460    * @see #floatToIntBits(float)
 461    * @see #floatToRawIntBits(float)
 462    */
 463   // GCJ LOCAL: We diverge from Classpath for efficiency.
 464   public static native float intBitsToFloat(int bits);
 465   // END GCJ LOCAL
 466
 467   /**
 468    * Compare two Floats numerically by comparing their <code>float</code>
 469    * values. The result is positive if the first is greater, negative if the
 470    * second is greater, and 0 if the two are equal. However, this special
 471    * cases NaN and signed zero as follows: NaN is considered greater than
 472    * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
 473    * zero is considered greater than negative zero.
 474    *
 475    * @param f the Float to compare
 476    * @return the comparison
 477    * @since 1.2
 478    */
 479   public int compareTo(Float f)
 480   {
 481     return compare(value, f.value);
 482   }
 483
 484   /**
 485    * Behaves like <code>compareTo(Float)</code> unless the Object
 486    * is not an <code>Float</code>.
 487    *
 488    * @param o the object to compare
 489    * @return the comparison
 490    * @throws ClassCastException if the argument is not a <code>Float</code>
 491    * @see #compareTo(Float)
 492    * @see Comparable
 493    * @since 1.2
 494    */
 495   public int compareTo(Object o)
 496   {
 497     return compare(value, ((Float) o).value);
 498   }
 499
 500   /**
 501    * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
 502    * other words this compares two floats, special casing NaN and zero,
 503    * without the overhead of objects.
 504    *
 505    * @param x the first float to compare
 506    * @param y the second float to compare
 507    * @return the comparison
 508    * @since 1.4
 509    */
 510   public static int compare(float x, float y)
 511   {
 512     if (isNaN(x))
 513       return isNaN(y) ? 0 : 1;
 514     if (isNaN(y))
 515       return -1;
 516     // recall that 0.0 == -0.0, so we convert to infinities and try again
 517     if (x == 0 && y == 0)
 518       return (int) (1 / x - 1 / y);
 519     if (x == y)
 520       return 0;
 521
 522     return x > y ? 1 : -1;
 523   }
 524 }