Float.java revision 9524178a7300a939242b78017f3dfa8014d4ca6d
1/* 2 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26package java.lang; 27 28import sun.misc.FpUtils; 29import sun.misc.FloatConsts; 30import sun.misc.DoubleConsts; 31 32/** 33 * The {@code Float} class wraps a value of primitive type 34 * {@code float} in an object. An object of type 35 * {@code Float} contains a single field whose type is 36 * {@code float}. 37 * 38 * <p>In addition, this class provides several methods for converting a 39 * {@code float} to a {@code String} and a 40 * {@code String} to a {@code float}, as well as other 41 * constants and methods useful when dealing with a 42 * {@code float}. 43 * 44 * @author Lee Boynton 45 * @author Arthur van Hoff 46 * @author Joseph D. Darcy 47 * @since JDK1.0 48 */ 49public final class Float extends Number implements Comparable<Float> { 50 /** 51 * A constant holding the positive infinity of type 52 * {@code float}. It is equal to the value returned by 53 * {@code Float.intBitsToFloat(0x7f800000)}. 54 */ 55 public static final float POSITIVE_INFINITY = 1.0f / 0.0f; 56 57 /** 58 * A constant holding the negative infinity of type 59 * {@code float}. It is equal to the value returned by 60 * {@code Float.intBitsToFloat(0xff800000)}. 61 */ 62 public static final float NEGATIVE_INFINITY = -1.0f / 0.0f; 63 64 /** 65 * A constant holding a Not-a-Number (NaN) value of type 66 * {@code float}. It is equivalent to the value returned by 67 * {@code Float.intBitsToFloat(0x7fc00000)}. 68 */ 69 public static final float NaN = 0.0f / 0.0f; 70 71 /** 72 * A constant holding the largest positive finite value of type 73 * {@code float}, (2-2<sup>-23</sup>)·2<sup>127</sup>. 74 * It is equal to the hexadecimal floating-point literal 75 * {@code 0x1.fffffeP+127f} and also equal to 76 * {@code Float.intBitsToFloat(0x7f7fffff)}. 77 */ 78 public static final float MAX_VALUE = 0x1.fffffeP+127f; // 3.4028235e+38f 79 80 /** 81 * A constant holding the smallest positive normal value of type 82 * {@code float}, 2<sup>-126</sup>. It is equal to the 83 * hexadecimal floating-point literal {@code 0x1.0p-126f} and also 84 * equal to {@code Float.intBitsToFloat(0x00800000)}. 85 * 86 * @since 1.6 87 */ 88 public static final float MIN_NORMAL = 0x1.0p-126f; // 1.17549435E-38f 89 90 /** 91 * A constant holding the smallest positive nonzero value of type 92 * {@code float}, 2<sup>-149</sup>. It is equal to the 93 * hexadecimal floating-point literal {@code 0x0.000002P-126f} 94 * and also equal to {@code Float.intBitsToFloat(0x1)}. 95 */ 96 public static final float MIN_VALUE = 0x0.000002P-126f; // 1.4e-45f 97 98 /** 99 * Maximum exponent a finite {@code float} variable may have. It 100 * is equal to the value returned by {@code 101 * Math.getExponent(Float.MAX_VALUE)}. 102 * 103 * @since 1.6 104 */ 105 public static final int MAX_EXPONENT = 127; 106 107 /** 108 * Minimum exponent a normalized {@code float} variable may have. 109 * It is equal to the value returned by {@code 110 * Math.getExponent(Float.MIN_NORMAL)}. 111 * 112 * @since 1.6 113 */ 114 public static final int MIN_EXPONENT = -126; 115 116 /** 117 * The number of bits used to represent a {@code float} value. 118 * 119 * @since 1.5 120 */ 121 public static final int SIZE = 32; 122 123 /** 124 * The {@code Class} instance representing the primitive type 125 * {@code float}. 126 * 127 * @since JDK1.1 128 */ 129 public static final Class<Float> TYPE = (Class<Float>) float[].class.getComponentType(); 130 131 /** 132 * Returns a string representation of the {@code float} 133 * argument. All characters mentioned below are ASCII characters. 134 * <ul> 135 * <li>If the argument is NaN, the result is the string 136 * "{@code NaN}". 137 * <li>Otherwise, the result is a string that represents the sign and 138 * magnitude (absolute value) of the argument. If the sign is 139 * negative, the first character of the result is 140 * '{@code -}' (<code>'\u002D'</code>); if the sign is 141 * positive, no sign character appears in the result. As for 142 * the magnitude <i>m</i>: 143 * <ul> 144 * <li>If <i>m</i> is infinity, it is represented by the characters 145 * {@code "Infinity"}; thus, positive infinity produces 146 * the result {@code "Infinity"} and negative infinity 147 * produces the result {@code "-Infinity"}. 148 * <li>If <i>m</i> is zero, it is represented by the characters 149 * {@code "0.0"}; thus, negative zero produces the result 150 * {@code "-0.0"} and positive zero produces the result 151 * {@code "0.0"}. 152 * <li> If <i>m</i> is greater than or equal to 10<sup>-3</sup> but 153 * less than 10<sup>7</sup>, then it is represented as the 154 * integer part of <i>m</i>, in decimal form with no leading 155 * zeroes, followed by '{@code .}' 156 * (<code>'\u002E'</code>), followed by one or more 157 * decimal digits representing the fractional part of 158 * <i>m</i>. 159 * <li> If <i>m</i> is less than 10<sup>-3</sup> or greater than or 160 * equal to 10<sup>7</sup>, then it is represented in 161 * so-called "computerized scientific notation." Let <i>n</i> 162 * be the unique integer such that 10<sup><i>n</i> </sup>≤ 163 * <i>m</i> {@literal <} 10<sup><i>n</i>+1</sup>; then let <i>a</i> 164 * be the mathematically exact quotient of <i>m</i> and 165 * 10<sup><i>n</i></sup> so that 1 ≤ <i>a</i> {@literal <} 10. 166 * The magnitude is then represented as the integer part of 167 * <i>a</i>, as a single decimal digit, followed by 168 * '{@code .}' (<code>'\u002E'</code>), followed by 169 * decimal digits representing the fractional part of 170 * <i>a</i>, followed by the letter '{@code E}' 171 * (<code>'\u0045'</code>), followed by a representation 172 * of <i>n</i> as a decimal integer, as produced by the 173 * method {@link java.lang.Integer#toString(int)}. 174 * 175 * </ul> 176 * </ul> 177 * How many digits must be printed for the fractional part of 178 * <i>m</i> or <i>a</i>? There must be at least one digit 179 * to represent the fractional part, and beyond that as many, but 180 * only as many, more digits as are needed to uniquely distinguish 181 * the argument value from adjacent values of type 182 * {@code float}. That is, suppose that <i>x</i> is the 183 * exact mathematical value represented by the decimal 184 * representation produced by this method for a finite nonzero 185 * argument <i>f</i>. Then <i>f</i> must be the {@code float} 186 * value nearest to <i>x</i>; or, if two {@code float} values are 187 * equally close to <i>x</i>, then <i>f</i> must be one of 188 * them and the least significant bit of the significand of 189 * <i>f</i> must be {@code 0}. 190 * 191 * <p>To create localized string representations of a floating-point 192 * value, use subclasses of {@link java.text.NumberFormat}. 193 * 194 * @param f the float to be converted. 195 * @return a string representation of the argument. 196 */ 197 public static String toString(float f) { 198 return FloatingDecimal.getThreadLocalInstance().loadFloat(f).toJavaFormatString(); 199 } 200 201 /** 202 * Returns a hexadecimal string representation of the 203 * {@code float} argument. All characters mentioned below are 204 * ASCII characters. 205 * 206 * <ul> 207 * <li>If the argument is NaN, the result is the string 208 * "{@code NaN}". 209 * <li>Otherwise, the result is a string that represents the sign and 210 * magnitude (absolute value) of the argument. If the sign is negative, 211 * the first character of the result is '{@code -}' 212 * (<code>'\u002D'</code>); if the sign is positive, no sign character 213 * appears in the result. As for the magnitude <i>m</i>: 214 * 215 * <ul> 216 * <li>If <i>m</i> is infinity, it is represented by the string 217 * {@code "Infinity"}; thus, positive infinity produces the 218 * result {@code "Infinity"} and negative infinity produces 219 * the result {@code "-Infinity"}. 220 * 221 * <li>If <i>m</i> is zero, it is represented by the string 222 * {@code "0x0.0p0"}; thus, negative zero produces the result 223 * {@code "-0x0.0p0"} and positive zero produces the result 224 * {@code "0x0.0p0"}. 225 * 226 * <li>If <i>m</i> is a {@code float} value with a 227 * normalized representation, substrings are used to represent the 228 * significand and exponent fields. The significand is 229 * represented by the characters {@code "0x1."} 230 * followed by a lowercase hexadecimal representation of the rest 231 * of the significand as a fraction. Trailing zeros in the 232 * hexadecimal representation are removed unless all the digits 233 * are zero, in which case a single zero is used. Next, the 234 * exponent is represented by {@code "p"} followed 235 * by a decimal string of the unbiased exponent as if produced by 236 * a call to {@link Integer#toString(int) Integer.toString} on the 237 * exponent value. 238 * 239 * <li>If <i>m</i> is a {@code float} value with a subnormal 240 * representation, the significand is represented by the 241 * characters {@code "0x0."} followed by a 242 * hexadecimal representation of the rest of the significand as a 243 * fraction. Trailing zeros in the hexadecimal representation are 244 * removed. Next, the exponent is represented by 245 * {@code "p-126"}. Note that there must be at 246 * least one nonzero digit in a subnormal significand. 247 * 248 * </ul> 249 * 250 * </ul> 251 * 252 * <table border> 253 * <caption><h3>Examples</h3></caption> 254 * <tr><th>Floating-point Value</th><th>Hexadecimal String</th> 255 * <tr><td>{@code 1.0}</td> <td>{@code 0x1.0p0}</td> 256 * <tr><td>{@code -1.0}</td> <td>{@code -0x1.0p0}</td> 257 * <tr><td>{@code 2.0}</td> <td>{@code 0x1.0p1}</td> 258 * <tr><td>{@code 3.0}</td> <td>{@code 0x1.8p1}</td> 259 * <tr><td>{@code 0.5}</td> <td>{@code 0x1.0p-1}</td> 260 * <tr><td>{@code 0.25}</td> <td>{@code 0x1.0p-2}</td> 261 * <tr><td>{@code Float.MAX_VALUE}</td> 262 * <td>{@code 0x1.fffffep127}</td> 263 * <tr><td>{@code Minimum Normal Value}</td> 264 * <td>{@code 0x1.0p-126}</td> 265 * <tr><td>{@code Maximum Subnormal Value}</td> 266 * <td>{@code 0x0.fffffep-126}</td> 267 * <tr><td>{@code Float.MIN_VALUE}</td> 268 * <td>{@code 0x0.000002p-126}</td> 269 * </table> 270 * @param f the {@code float} to be converted. 271 * @return a hex string representation of the argument. 272 * @since 1.5 273 * @author Joseph D. Darcy 274 */ 275 public static String toHexString(float f) { 276 if (Math.abs(f) < FloatConsts.MIN_NORMAL 277 && f != 0.0f ) {// float subnormal 278 // Adjust exponent to create subnormal double, then 279 // replace subnormal double exponent with subnormal float 280 // exponent 281 String s = Double.toHexString(FpUtils.scalb((double)f, 282 /* -1022+126 */ 283 DoubleConsts.MIN_EXPONENT- 284 FloatConsts.MIN_EXPONENT)); 285 return s.replaceFirst("p-1022$", "p-126"); 286 } 287 else // double string will be the same as float string 288 return Double.toHexString(f); 289 } 290 291 /** 292 * Returns a {@code Float} object holding the 293 * {@code float} value represented by the argument string 294 * {@code s}. 295 * 296 * <p>If {@code s} is {@code null}, then a 297 * {@code NullPointerException} is thrown. 298 * 299 * <p>Leading and trailing whitespace characters in {@code s} 300 * are ignored. Whitespace is removed as if by the {@link 301 * String#trim} method; that is, both ASCII space and control 302 * characters are removed. The rest of {@code s} should 303 * constitute a <i>FloatValue</i> as described by the lexical 304 * syntax rules: 305 * 306 * <blockquote> 307 * <dl> 308 * <dt><i>FloatValue:</i> 309 * <dd><i>Sign<sub>opt</sub></i> {@code NaN} 310 * <dd><i>Sign<sub>opt</sub></i> {@code Infinity} 311 * <dd><i>Sign<sub>opt</sub> FloatingPointLiteral</i> 312 * <dd><i>Sign<sub>opt</sub> HexFloatingPointLiteral</i> 313 * <dd><i>SignedInteger</i> 314 * </dl> 315 * 316 * <p> 317 * 318 * <dl> 319 * <dt><i>HexFloatingPointLiteral</i>: 320 * <dd> <i>HexSignificand BinaryExponent FloatTypeSuffix<sub>opt</sub></i> 321 * </dl> 322 * 323 * <p> 324 * 325 * <dl> 326 * <dt><i>HexSignificand:</i> 327 * <dd><i>HexNumeral</i> 328 * <dd><i>HexNumeral</i> {@code .} 329 * <dd>{@code 0x} <i>HexDigits<sub>opt</sub> 330 * </i>{@code .}<i> HexDigits</i> 331 * <dd>{@code 0X}<i> HexDigits<sub>opt</sub> 332 * </i>{@code .} <i>HexDigits</i> 333 * </dl> 334 * 335 * <p> 336 * 337 * <dl> 338 * <dt><i>BinaryExponent:</i> 339 * <dd><i>BinaryExponentIndicator SignedInteger</i> 340 * </dl> 341 * 342 * <p> 343 * 344 * <dl> 345 * <dt><i>BinaryExponentIndicator:</i> 346 * <dd>{@code p} 347 * <dd>{@code P} 348 * </dl> 349 * 350 * </blockquote> 351 * 352 * where <i>Sign</i>, <i>FloatingPointLiteral</i>, 353 * <i>HexNumeral</i>, <i>HexDigits</i>, <i>SignedInteger</i> and 354 * <i>FloatTypeSuffix</i> are as defined in the lexical structure 355 * sections of 356 * <cite>The Java™ Language Specification</cite>, 357 * except that underscores are not accepted between digits. 358 * If {@code s} does not have the form of 359 * a <i>FloatValue</i>, then a {@code NumberFormatException} 360 * is thrown. Otherwise, {@code s} is regarded as 361 * representing an exact decimal value in the usual 362 * "computerized scientific notation" or as an exact 363 * hexadecimal value; this exact numerical value is then 364 * conceptually converted to an "infinitely precise" 365 * binary value that is then rounded to type {@code float} 366 * by the usual round-to-nearest rule of IEEE 754 floating-point 367 * arithmetic, which includes preserving the sign of a zero 368 * value. 369 * 370 * Note that the round-to-nearest rule also implies overflow and 371 * underflow behaviour; if the exact value of {@code s} is large 372 * enough in magnitude (greater than or equal to ({@link 373 * #MAX_VALUE} + {@link Math#ulp(float) ulp(MAX_VALUE)}/2), 374 * rounding to {@code float} will result in an infinity and if the 375 * exact value of {@code s} is small enough in magnitude (less 376 * than or equal to {@link #MIN_VALUE}/2), rounding to float will 377 * result in a zero. 378 * 379 * Finally, after rounding a {@code Float} object representing 380 * this {@code float} value is returned. 381 * 382 * <p>To interpret localized string representations of a 383 * floating-point value, use subclasses of {@link 384 * java.text.NumberFormat}. 385 * 386 * <p>Note that trailing format specifiers, specifiers that 387 * determine the type of a floating-point literal 388 * ({@code 1.0f} is a {@code float} value; 389 * {@code 1.0d} is a {@code double} value), do 390 * <em>not</em> influence the results of this method. In other 391 * words, the numerical value of the input string is converted 392 * directly to the target floating-point type. In general, the 393 * two-step sequence of conversions, string to {@code double} 394 * followed by {@code double} to {@code float}, is 395 * <em>not</em> equivalent to converting a string directly to 396 * {@code float}. For example, if first converted to an 397 * intermediate {@code double} and then to 398 * {@code float}, the string<br> 399 * {@code "1.00000017881393421514957253748434595763683319091796875001d"}<br> 400 * results in the {@code float} value 401 * {@code 1.0000002f}; if the string is converted directly to 402 * {@code float}, <code>1.000000<b>1</b>f</code> results. 403 * 404 * <p>To avoid calling this method on an invalid string and having 405 * a {@code NumberFormatException} be thrown, the documentation 406 * for {@link Double#valueOf Double.valueOf} lists a regular 407 * expression which can be used to screen the input. 408 * 409 * @param s the string to be parsed. 410 * @return a {@code Float} object holding the value 411 * represented by the {@code String} argument. 412 * @throws NumberFormatException if the string does not contain a 413 * parsable number. 414 */ 415 public static Float valueOf(String s) throws NumberFormatException { 416 return new Float(FloatingDecimal.getThreadLocalInstance().readJavaFormatString(s).floatValue()); 417 } 418 419 /** 420 * Returns a {@code Float} instance representing the specified 421 * {@code float} value. 422 * If a new {@code Float} instance is not required, this method 423 * should generally be used in preference to the constructor 424 * {@link #Float(float)}, as this method is likely to yield 425 * significantly better space and time performance by caching 426 * frequently requested values. 427 * 428 * @param f a float value. 429 * @return a {@code Float} instance representing {@code f}. 430 * @since 1.5 431 */ 432 public static Float valueOf(float f) { 433 return new Float(f); 434 } 435 436 /** 437 * Returns a new {@code float} initialized to the value 438 * represented by the specified {@code String}, as performed 439 * by the {@code valueOf} method of class {@code Float}. 440 * 441 * @param s the string to be parsed. 442 * @return the {@code float} value represented by the string 443 * argument. 444 * @throws NullPointerException if the string is null 445 * @throws NumberFormatException if the string does not contain a 446 * parsable {@code float}. 447 * @see java.lang.Float#valueOf(String) 448 * @since 1.2 449 */ 450 public static float parseFloat(String s) throws NumberFormatException { 451 return FloatingDecimal.getThreadLocalInstance().readJavaFormatString(s).floatValue(); 452 } 453 454 /** 455 * Returns {@code true} if the specified number is a 456 * Not-a-Number (NaN) value, {@code false} otherwise. 457 * 458 * @param v the value to be tested. 459 * @return {@code true} if the argument is NaN; 460 * {@code false} otherwise. 461 */ 462 static public boolean isNaN(float v) { 463 return (v != v); 464 } 465 466 /** 467 * Returns {@code true} if the specified number is infinitely 468 * large in magnitude, {@code false} otherwise. 469 * 470 * @param v the value to be tested. 471 * @return {@code true} if the argument is positive infinity or 472 * negative infinity; {@code false} otherwise. 473 */ 474 static public boolean isInfinite(float v) { 475 return (v == POSITIVE_INFINITY) || (v == NEGATIVE_INFINITY); 476 } 477 478 /** 479 * The value of the Float. 480 * 481 * @serial 482 */ 483 private final float value; 484 485 /** 486 * Constructs a newly allocated {@code Float} object that 487 * represents the primitive {@code float} argument. 488 * 489 * @param value the value to be represented by the {@code Float}. 490 */ 491 public Float(float value) { 492 this.value = value; 493 } 494 495 /** 496 * Constructs a newly allocated {@code Float} object that 497 * represents the argument converted to type {@code float}. 498 * 499 * @param value the value to be represented by the {@code Float}. 500 */ 501 public Float(double value) { 502 this.value = (float)value; 503 } 504 505 /** 506 * Constructs a newly allocated {@code Float} object that 507 * represents the floating-point value of type {@code float} 508 * represented by the string. The string is converted to a 509 * {@code float} value as if by the {@code valueOf} method. 510 * 511 * @param s a string to be converted to a {@code Float}. 512 * @throws NumberFormatException if the string does not contain a 513 * parsable number. 514 * @see java.lang.Float#valueOf(java.lang.String) 515 */ 516 public Float(String s) throws NumberFormatException { 517 // REMIND: this is inefficient 518 this(valueOf(s).floatValue()); 519 } 520 521 /** 522 * Returns {@code true} if this {@code Float} value is a 523 * Not-a-Number (NaN), {@code false} otherwise. 524 * 525 * @return {@code true} if the value represented by this object is 526 * NaN; {@code false} otherwise. 527 */ 528 public boolean isNaN() { 529 return isNaN(value); 530 } 531 532 /** 533 * Returns {@code true} if this {@code Float} value is 534 * infinitely large in magnitude, {@code false} otherwise. 535 * 536 * @return {@code true} if the value represented by this object is 537 * positive infinity or negative infinity; 538 * {@code false} otherwise. 539 */ 540 public boolean isInfinite() { 541 return isInfinite(value); 542 } 543 544 /** 545 * Returns a string representation of this {@code Float} object. 546 * The primitive {@code float} value represented by this object 547 * is converted to a {@code String} exactly as if by the method 548 * {@code toString} of one argument. 549 * 550 * @return a {@code String} representation of this object. 551 * @see java.lang.Float#toString(float) 552 */ 553 public String toString() { 554 return Float.toString(value); 555 } 556 557 /** 558 * Returns the value of this {@code Float} as a {@code byte} (by 559 * casting to a {@code byte}). 560 * 561 * @return the {@code float} value represented by this object 562 * converted to type {@code byte} 563 */ 564 public byte byteValue() { 565 return (byte)value; 566 } 567 568 /** 569 * Returns the value of this {@code Float} as a {@code short} (by 570 * casting to a {@code short}). 571 * 572 * @return the {@code float} value represented by this object 573 * converted to type {@code short} 574 * @since JDK1.1 575 */ 576 public short shortValue() { 577 return (short)value; 578 } 579 580 /** 581 * Returns the value of this {@code Float} as an {@code int} (by 582 * casting to type {@code int}). 583 * 584 * @return the {@code float} value represented by this object 585 * converted to type {@code int} 586 */ 587 public int intValue() { 588 return (int)value; 589 } 590 591 /** 592 * Returns value of this {@code Float} as a {@code long} (by 593 * casting to type {@code long}). 594 * 595 * @return the {@code float} value represented by this object 596 * converted to type {@code long} 597 */ 598 public long longValue() { 599 return (long)value; 600 } 601 602 /** 603 * Returns the {@code float} value of this {@code Float} object. 604 * 605 * @return the {@code float} value represented by this object 606 */ 607 public float floatValue() { 608 return value; 609 } 610 611 /** 612 * Returns the {@code double} value of this {@code Float} object. 613 * 614 * @return the {@code float} value represented by this 615 * object is converted to type {@code double} and the 616 * result of the conversion is returned. 617 */ 618 public double doubleValue() { 619 return (double)value; 620 } 621 622 /** 623 * Returns a hash code for this {@code Float} object. The 624 * result is the integer bit representation, exactly as produced 625 * by the method {@link #floatToIntBits(float)}, of the primitive 626 * {@code float} value represented by this {@code Float} 627 * object. 628 * 629 * @return a hash code value for this object. 630 */ 631 public int hashCode() { 632 return floatToIntBits(value); 633 } 634 635 /** 636 637 * Compares this object against the specified object. The result 638 * is {@code true} if and only if the argument is not 639 * {@code null} and is a {@code Float} object that 640 * represents a {@code float} with the same value as the 641 * {@code float} represented by this object. For this 642 * purpose, two {@code float} values are considered to be the 643 * same if and only if the method {@link #floatToIntBits(float)} 644 * returns the identical {@code int} value when applied to 645 * each. 646 * 647 * <p>Note that in most cases, for two instances of class 648 * {@code Float}, {@code f1} and {@code f2}, the value 649 * of {@code f1.equals(f2)} is {@code true} if and only if 650 * 651 * <blockquote><pre> 652 * f1.floatValue() == f2.floatValue() 653 * </pre></blockquote> 654 * 655 * <p>also has the value {@code true}. However, there are two exceptions: 656 * <ul> 657 * <li>If {@code f1} and {@code f2} both represent 658 * {@code Float.NaN}, then the {@code equals} method returns 659 * {@code true}, even though {@code Float.NaN==Float.NaN} 660 * has the value {@code false}. 661 * <li>If {@code f1} represents {@code +0.0f} while 662 * {@code f2} represents {@code -0.0f}, or vice 663 * versa, the {@code equal} test has the value 664 * {@code false}, even though {@code 0.0f==-0.0f} 665 * has the value {@code true}. 666 * </ul> 667 * 668 * This definition allows hash tables to operate properly. 669 * 670 * @param obj the object to be compared 671 * @return {@code true} if the objects are the same; 672 * {@code false} otherwise. 673 * @see java.lang.Float#floatToIntBits(float) 674 */ 675 public boolean equals(Object obj) { 676 return (obj instanceof Float) 677 && (floatToIntBits(((Float)obj).value) == floatToIntBits(value)); 678 } 679 680 /** 681 * Returns a representation of the specified floating-point value 682 * according to the IEEE 754 floating-point "single format" bit 683 * layout. 684 * 685 * <p>Bit 31 (the bit that is selected by the mask 686 * {@code 0x80000000}) represents the sign of the floating-point 687 * number. 688 * Bits 30-23 (the bits that are selected by the mask 689 * {@code 0x7f800000}) represent the exponent. 690 * Bits 22-0 (the bits that are selected by the mask 691 * {@code 0x007fffff}) represent the significand (sometimes called 692 * the mantissa) of the floating-point number. 693 * 694 * <p>If the argument is positive infinity, the result is 695 * {@code 0x7f800000}. 696 * 697 * <p>If the argument is negative infinity, the result is 698 * {@code 0xff800000}. 699 * 700 * <p>If the argument is NaN, the result is {@code 0x7fc00000}. 701 * 702 * <p>In all cases, the result is an integer that, when given to the 703 * {@link #intBitsToFloat(int)} method, will produce a floating-point 704 * value the same as the argument to {@code floatToIntBits} 705 * (except all NaN values are collapsed to a single 706 * "canonical" NaN value). 707 * 708 * @param value a floating-point number. 709 * @return the bits that represent the floating-point number. 710 */ 711 public static int floatToIntBits(float value) { 712 int result = floatToRawIntBits(value); 713 // Check for NaN based on values of bit fields, maximum 714 // exponent and nonzero significand. 715 if ( ((result & FloatConsts.EXP_BIT_MASK) == 716 FloatConsts.EXP_BIT_MASK) && 717 (result & FloatConsts.SIGNIF_BIT_MASK) != 0) 718 result = 0x7fc00000; 719 return result; 720 } 721 722 /** 723 * Returns a representation of the specified floating-point value 724 * according to the IEEE 754 floating-point "single format" bit 725 * layout, preserving Not-a-Number (NaN) values. 726 * 727 * <p>Bit 31 (the bit that is selected by the mask 728 * {@code 0x80000000}) represents the sign of the floating-point 729 * number. 730 * Bits 30-23 (the bits that are selected by the mask 731 * {@code 0x7f800000}) represent the exponent. 732 * Bits 22-0 (the bits that are selected by the mask 733 * {@code 0x007fffff}) represent the significand (sometimes called 734 * the mantissa) of the floating-point number. 735 * 736 * <p>If the argument is positive infinity, the result is 737 * {@code 0x7f800000}. 738 * 739 * <p>If the argument is negative infinity, the result is 740 * {@code 0xff800000}. 741 * 742 * <p>If the argument is NaN, the result is the integer representing 743 * the actual NaN value. Unlike the {@code floatToIntBits} 744 * method, {@code floatToRawIntBits} does not collapse all the 745 * bit patterns encoding a NaN to a single "canonical" 746 * NaN value. 747 * 748 * <p>In all cases, the result is an integer that, when given to the 749 * {@link #intBitsToFloat(int)} method, will produce a 750 * floating-point value the same as the argument to 751 * {@code floatToRawIntBits}. 752 * 753 * @param value a floating-point number. 754 * @return the bits that represent the floating-point number. 755 * @since 1.3 756 */ 757 public static native int floatToRawIntBits(float value); 758 759 /** 760 * Returns the {@code float} value corresponding to a given 761 * bit representation. 762 * The argument is considered to be a representation of a 763 * floating-point value according to the IEEE 754 floating-point 764 * "single format" bit layout. 765 * 766 * <p>If the argument is {@code 0x7f800000}, the result is positive 767 * infinity. 768 * 769 * <p>If the argument is {@code 0xff800000}, the result is negative 770 * infinity. 771 * 772 * <p>If the argument is any value in the range 773 * {@code 0x7f800001} through {@code 0x7fffffff} or in 774 * the range {@code 0xff800001} through 775 * {@code 0xffffffff}, the result is a NaN. No IEEE 754 776 * floating-point operation provided by Java can distinguish 777 * between two NaN values of the same type with different bit 778 * patterns. Distinct values of NaN are only distinguishable by 779 * use of the {@code Float.floatToRawIntBits} method. 780 * 781 * <p>In all other cases, let <i>s</i>, <i>e</i>, and <i>m</i> be three 782 * values that can be computed from the argument: 783 * 784 * <blockquote><pre> 785 * int s = ((bits >> 31) == 0) ? 1 : -1; 786 * int e = ((bits >> 23) & 0xff); 787 * int m = (e == 0) ? 788 * (bits & 0x7fffff) << 1 : 789 * (bits & 0x7fffff) | 0x800000; 790 * </pre></blockquote> 791 * 792 * Then the floating-point result equals the value of the mathematical 793 * expression <i>s</i>·<i>m</i>·2<sup><i>e</i>-150</sup>. 794 * 795 * <p>Note that this method may not be able to return a 796 * {@code float} NaN with exactly same bit pattern as the 797 * {@code int} argument. IEEE 754 distinguishes between two 798 * kinds of NaNs, quiet NaNs and <i>signaling NaNs</i>. The 799 * differences between the two kinds of NaN are generally not 800 * visible in Java. Arithmetic operations on signaling NaNs turn 801 * them into quiet NaNs with a different, but often similar, bit 802 * pattern. However, on some processors merely copying a 803 * signaling NaN also performs that conversion. In particular, 804 * copying a signaling NaN to return it to the calling method may 805 * perform this conversion. So {@code intBitsToFloat} may 806 * not be able to return a {@code float} with a signaling NaN 807 * bit pattern. Consequently, for some {@code int} values, 808 * {@code floatToRawIntBits(intBitsToFloat(start))} may 809 * <i>not</i> equal {@code start}. Moreover, which 810 * particular bit patterns represent signaling NaNs is platform 811 * dependent; although all NaN bit patterns, quiet or signaling, 812 * must be in the NaN range identified above. 813 * 814 * @param bits an integer. 815 * @return the {@code float} floating-point value with the same bit 816 * pattern. 817 */ 818 public static native float intBitsToFloat(int bits); 819 820 /** 821 * Compares two {@code Float} objects numerically. There are 822 * two ways in which comparisons performed by this method differ 823 * from those performed by the Java language numerical comparison 824 * operators ({@code <, <=, ==, >=, >}) when 825 * applied to primitive {@code float} values: 826 * 827 * <ul><li> 828 * {@code Float.NaN} is considered by this method to 829 * be equal to itself and greater than all other 830 * {@code float} values 831 * (including {@code Float.POSITIVE_INFINITY}). 832 * <li> 833 * {@code 0.0f} is considered by this method to be greater 834 * than {@code -0.0f}. 835 * </ul> 836 * 837 * This ensures that the <i>natural ordering</i> of {@code Float} 838 * objects imposed by this method is <i>consistent with equals</i>. 839 * 840 * @param anotherFloat the {@code Float} to be compared. 841 * @return the value {@code 0} if {@code anotherFloat} is 842 * numerically equal to this {@code Float}; a value 843 * less than {@code 0} if this {@code Float} 844 * is numerically less than {@code anotherFloat}; 845 * and a value greater than {@code 0} if this 846 * {@code Float} is numerically greater than 847 * {@code anotherFloat}. 848 * 849 * @since 1.2 850 * @see Comparable#compareTo(Object) 851 */ 852 public int compareTo(Float anotherFloat) { 853 return Float.compare(value, anotherFloat.value); 854 } 855 856 /** 857 * Compares the two specified {@code float} values. The sign 858 * of the integer value returned is the same as that of the 859 * integer that would be returned by the call: 860 * <pre> 861 * new Float(f1).compareTo(new Float(f2)) 862 * </pre> 863 * 864 * @param f1 the first {@code float} to compare. 865 * @param f2 the second {@code float} to compare. 866 * @return the value {@code 0} if {@code f1} is 867 * numerically equal to {@code f2}; a value less than 868 * {@code 0} if {@code f1} is numerically less than 869 * {@code f2}; and a value greater than {@code 0} 870 * if {@code f1} is numerically greater than 871 * {@code f2}. 872 * @since 1.4 873 */ 874 public static int compare(float f1, float f2) { 875 if (f1 < f2) 876 return -1; // Neither val is NaN, thisVal is smaller 877 if (f1 > f2) 878 return 1; // Neither val is NaN, thisVal is larger 879 880 // Cannot use floatToRawIntBits because of possibility of NaNs. 881 int thisBits = Float.floatToIntBits(f1); 882 int anotherBits = Float.floatToIntBits(f2); 883 884 return (thisBits == anotherBits ? 0 : // Values are equal 885 (thisBits < anotherBits ? -1 : // (-0.0, 0.0) or (!NaN, NaN) 886 1)); // (0.0, -0.0) or (NaN, !NaN) 887 } 888 889 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 890 private static final long serialVersionUID = -2671257302660747028L; 891} 892