001/* 002 * Copyright (C) 2008 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.primitives; 016 017import static com.google.common.base.Preconditions.checkArgument; 018import static com.google.common.base.Preconditions.checkElementIndex; 019import static com.google.common.base.Preconditions.checkNotNull; 020import static com.google.common.base.Preconditions.checkPositionIndexes; 021import static com.google.common.base.Strings.lenientFormat; 022import static java.lang.Double.NEGATIVE_INFINITY; 023import static java.lang.Double.POSITIVE_INFINITY; 024 025import com.google.common.annotations.GwtCompatible; 026import com.google.common.annotations.GwtIncompatible; 027import com.google.common.annotations.J2ktIncompatible; 028import com.google.common.base.Converter; 029import java.io.Serializable; 030import java.util.AbstractList; 031import java.util.Arrays; 032import java.util.Collection; 033import java.util.Collections; 034import java.util.Comparator; 035import java.util.List; 036import java.util.RandomAccess; 037import java.util.Spliterator; 038import java.util.Spliterators; 039import javax.annotation.CheckForNull; 040 041/** 042 * Static utility methods pertaining to {@code double} primitives, that are not already found in 043 * either {@link Double} or {@link Arrays}. 044 * 045 * <p>See the Guava User Guide article on <a 046 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>. 047 * 048 * @author Kevin Bourrillion 049 * @since 1.0 050 */ 051@GwtCompatible(emulated = true) 052@ElementTypesAreNonnullByDefault 053public final class Doubles extends DoublesMethodsForWeb { 054 private Doubles() {} 055 056 /** 057 * The number of bytes required to represent a primitive {@code double} value. 058 * 059 * <p><b>Java 8 users:</b> use {@link Double#BYTES} instead. 060 * 061 * @since 10.0 062 */ 063 public static final int BYTES = Double.SIZE / Byte.SIZE; 064 065 /** 066 * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Double) 067 * value).hashCode()}. 068 * 069 * <p><b>Java 8 users:</b> use {@link Double#hashCode(double)} instead. 070 * 071 * @param value a primitive {@code double} value 072 * @return a hash code for the value 073 */ 074 public static int hashCode(double value) { 075 return ((Double) value).hashCode(); 076 // TODO(kevinb): do it this way when we can (GWT problem): 077 // long bits = Double.doubleToLongBits(value); 078 // return (int) (bits ^ (bits >>> 32)); 079 } 080 081 /** 082 * Compares the two specified {@code double} values. The sign of the value returned is the same as 083 * that of <code>((Double) a).{@linkplain Double#compareTo compareTo}(b)</code>. As with that 084 * method, {@code NaN} is treated as greater than all other values, and {@code 0.0 > -0.0}. 085 * 086 * <p><b>Note:</b> this method simply delegates to the JDK method {@link Double#compare}. It is 087 * provided for consistency with the other primitive types, whose compare methods were not added 088 * to the JDK until JDK 7. 089 * 090 * @param a the first {@code double} to compare 091 * @param b the second {@code double} to compare 092 * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is 093 * greater than {@code b}; or zero if they are equal 094 */ 095 public static int compare(double a, double b) { 096 return Double.compare(a, b); 097 } 098 099 /** 100 * Returns {@code true} if {@code value} represents a real number. This is equivalent to, but not 101 * necessarily implemented as, {@code !(Double.isInfinite(value) || Double.isNaN(value))}. 102 * 103 * <p><b>Java 8 users:</b> use {@link Double#isFinite(double)} instead. 104 * 105 * @since 10.0 106 */ 107 public static boolean isFinite(double value) { 108 return NEGATIVE_INFINITY < value && value < POSITIVE_INFINITY; 109 } 110 111 /** 112 * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}. Note 113 * that this always returns {@code false} when {@code target} is {@code NaN}. 114 * 115 * @param array an array of {@code double} values, possibly empty 116 * @param target a primitive {@code double} value 117 * @return {@code true} if {@code array[i] == target} for some value of {@code i} 118 */ 119 public static boolean contains(double[] array, double target) { 120 for (double value : array) { 121 if (value == target) { 122 return true; 123 } 124 } 125 return false; 126 } 127 128 /** 129 * Returns the index of the first appearance of the value {@code target} in {@code array}. Note 130 * that this always returns {@code -1} when {@code target} is {@code NaN}. 131 * 132 * @param array an array of {@code double} values, possibly empty 133 * @param target a primitive {@code double} value 134 * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no 135 * such index exists. 136 */ 137 public static int indexOf(double[] array, double target) { 138 return indexOf(array, target, 0, array.length); 139 } 140 141 // TODO(kevinb): consider making this public 142 private static int indexOf(double[] array, double target, int start, int end) { 143 for (int i = start; i < end; i++) { 144 if (array[i] == target) { 145 return i; 146 } 147 } 148 return -1; 149 } 150 151 /** 152 * Returns the start position of the first occurrence of the specified {@code target} within 153 * {@code array}, or {@code -1} if there is no such occurrence. 154 * 155 * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array, 156 * i, i + target.length)} contains exactly the same elements as {@code target}. 157 * 158 * <p>Note that this always returns {@code -1} when {@code target} contains {@code NaN}. 159 * 160 * @param array the array to search for the sequence {@code target} 161 * @param target the array to search for as a sub-sequence of {@code array} 162 */ 163 public static int indexOf(double[] array, double[] target) { 164 checkNotNull(array, "array"); 165 checkNotNull(target, "target"); 166 if (target.length == 0) { 167 return 0; 168 } 169 170 outer: 171 for (int i = 0; i < array.length - target.length + 1; i++) { 172 for (int j = 0; j < target.length; j++) { 173 if (array[i + j] != target[j]) { 174 continue outer; 175 } 176 } 177 return i; 178 } 179 return -1; 180 } 181 182 /** 183 * Returns the index of the last appearance of the value {@code target} in {@code array}. Note 184 * that this always returns {@code -1} when {@code target} is {@code NaN}. 185 * 186 * @param array an array of {@code double} values, possibly empty 187 * @param target a primitive {@code double} value 188 * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no 189 * such index exists. 190 */ 191 public static int lastIndexOf(double[] array, double target) { 192 return lastIndexOf(array, target, 0, array.length); 193 } 194 195 // TODO(kevinb): consider making this public 196 private static int lastIndexOf(double[] array, double target, int start, int end) { 197 for (int i = end - 1; i >= start; i--) { 198 if (array[i] == target) { 199 return i; 200 } 201 } 202 return -1; 203 } 204 205 /** 206 * Returns the least value present in {@code array}, using the same rules of comparison as {@link 207 * Math#min(double, double)}. 208 * 209 * @param array a <i>nonempty</i> array of {@code double} values 210 * @return the value present in {@code array} that is less than or equal to every other value in 211 * the array 212 * @throws IllegalArgumentException if {@code array} is empty 213 */ 214 @GwtIncompatible( 215 "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.") 216 public static double min(double... array) { 217 checkArgument(array.length > 0); 218 double min = array[0]; 219 for (int i = 1; i < array.length; i++) { 220 min = Math.min(min, array[i]); 221 } 222 return min; 223 } 224 225 /** 226 * Returns the greatest value present in {@code array}, using the same rules of comparison as 227 * {@link Math#max(double, double)}. 228 * 229 * @param array a <i>nonempty</i> array of {@code double} values 230 * @return the value present in {@code array} that is greater than or equal to every other value 231 * in the array 232 * @throws IllegalArgumentException if {@code array} is empty 233 */ 234 @GwtIncompatible( 235 "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.") 236 public static double max(double... array) { 237 checkArgument(array.length > 0); 238 double max = array[0]; 239 for (int i = 1; i < array.length; i++) { 240 max = Math.max(max, array[i]); 241 } 242 return max; 243 } 244 245 /** 246 * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}. 247 * 248 * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned 249 * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code 250 * value} is greater than {@code max}, {@code max} is returned. 251 * 252 * @param value the {@code double} value to constrain 253 * @param min the lower bound (inclusive) of the range to constrain {@code value} to 254 * @param max the upper bound (inclusive) of the range to constrain {@code value} to 255 * @throws IllegalArgumentException if {@code min > max} 256 * @since 21.0 257 */ 258 public static double constrainToRange(double value, double min, double max) { 259 // avoid auto-boxing by not using Preconditions.checkArgument(); see Guava issue 3984 260 // Reject NaN by testing for the good case (min <= max) instead of the bad (min > max). 261 if (min <= max) { 262 return Math.min(Math.max(value, min), max); 263 } 264 throw new IllegalArgumentException( 265 lenientFormat("min (%s) must be less than or equal to max (%s)", min, max)); 266 } 267 268 /** 269 * Returns the values from each provided array combined into a single array. For example, {@code 270 * concat(new double[] {a, b}, new double[] {}, new double[] {c}} returns the array {@code {a, b, 271 * c}}. 272 * 273 * @param arrays zero or more {@code double} arrays 274 * @return a single array containing all the values from the source arrays, in order 275 */ 276 public static double[] concat(double[]... arrays) { 277 int length = 0; 278 for (double[] array : arrays) { 279 length += array.length; 280 } 281 double[] result = new double[length]; 282 int pos = 0; 283 for (double[] array : arrays) { 284 System.arraycopy(array, 0, result, pos, array.length); 285 pos += array.length; 286 } 287 return result; 288 } 289 290 private static final class DoubleConverter extends Converter<String, Double> 291 implements Serializable { 292 static final DoubleConverter INSTANCE = new DoubleConverter(); 293 294 @Override 295 protected Double doForward(String value) { 296 return Double.valueOf(value); 297 } 298 299 @Override 300 protected String doBackward(Double value) { 301 return value.toString(); 302 } 303 304 @Override 305 public String toString() { 306 return "Doubles.stringConverter()"; 307 } 308 309 private Object readResolve() { 310 return INSTANCE; 311 } 312 313 private static final long serialVersionUID = 1; 314 } 315 316 /** 317 * Returns a serializable converter object that converts between strings and doubles using {@link 318 * Double#valueOf} and {@link Double#toString()}. 319 * 320 * @since 16.0 321 */ 322 public static Converter<String, Double> stringConverter() { 323 return DoubleConverter.INSTANCE; 324 } 325 326 /** 327 * Returns an array containing the same values as {@code array}, but guaranteed to be of a 328 * specified minimum length. If {@code array} already has a length of at least {@code minLength}, 329 * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is 330 * returned, containing the values of {@code array}, and zeroes in the remaining places. 331 * 332 * @param array the source array 333 * @param minLength the minimum length the returned array must guarantee 334 * @param padding an extra amount to "grow" the array by if growth is necessary 335 * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative 336 * @return an array containing the values of {@code array}, with guaranteed minimum length {@code 337 * minLength} 338 */ 339 public static double[] ensureCapacity(double[] array, int minLength, int padding) { 340 checkArgument(minLength >= 0, "Invalid minLength: %s", minLength); 341 checkArgument(padding >= 0, "Invalid padding: %s", padding); 342 return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array; 343 } 344 345 /** 346 * Returns a string containing the supplied {@code double} values, converted to strings as 347 * specified by {@link Double#toString(double)}, and separated by {@code separator}. For example, 348 * {@code join("-", 1.0, 2.0, 3.0)} returns the string {@code "1.0-2.0-3.0"}. 349 * 350 * <p>Note that {@link Double#toString(double)} formats {@code double} differently in GWT 351 * sometimes. In the previous example, it returns the string {@code "1-2-3"}. 352 * 353 * @param separator the text that should appear between consecutive values in the resulting string 354 * (but not at the start or end) 355 * @param array an array of {@code double} values, possibly empty 356 */ 357 public static String join(String separator, double... array) { 358 checkNotNull(separator); 359 if (array.length == 0) { 360 return ""; 361 } 362 363 // For pre-sizing a builder, just get the right order of magnitude 364 StringBuilder builder = new StringBuilder(array.length * 12); 365 builder.append(array[0]); 366 for (int i = 1; i < array.length; i++) { 367 builder.append(separator).append(array[i]); 368 } 369 return builder.toString(); 370 } 371 372 /** 373 * Returns a comparator that compares two {@code double} arrays <a 374 * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it 375 * compares, using {@link #compare(double, double)}), the first pair of values that follow any 376 * common prefix, or when one array is a prefix of the other, treats the shorter array as the 377 * lesser. For example, {@code [] < [1.0] < [1.0, 2.0] < [2.0]}. 378 * 379 * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays 380 * support only identity equality), but it is consistent with {@link Arrays#equals(double[], 381 * double[])}. 382 * 383 * @since 2.0 384 */ 385 public static Comparator<double[]> lexicographicalComparator() { 386 return LexicographicalComparator.INSTANCE; 387 } 388 389 private enum LexicographicalComparator implements Comparator<double[]> { 390 INSTANCE; 391 392 @Override 393 public int compare(double[] left, double[] right) { 394 int minLength = Math.min(left.length, right.length); 395 for (int i = 0; i < minLength; i++) { 396 int result = Double.compare(left[i], right[i]); 397 if (result != 0) { 398 return result; 399 } 400 } 401 return left.length - right.length; 402 } 403 404 @Override 405 public String toString() { 406 return "Doubles.lexicographicalComparator()"; 407 } 408 } 409 410 /** 411 * Sorts the elements of {@code array} in descending order. 412 * 413 * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats 414 * all NaN values as equal and 0.0 as greater than -0.0. 415 * 416 * @since 23.1 417 */ 418 public static void sortDescending(double[] array) { 419 checkNotNull(array); 420 sortDescending(array, 0, array.length); 421 } 422 423 /** 424 * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex} 425 * exclusive in descending order. 426 * 427 * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats 428 * all NaN values as equal and 0.0 as greater than -0.0. 429 * 430 * @since 23.1 431 */ 432 public static void sortDescending(double[] array, int fromIndex, int toIndex) { 433 checkNotNull(array); 434 checkPositionIndexes(fromIndex, toIndex, array.length); 435 Arrays.sort(array, fromIndex, toIndex); 436 reverse(array, fromIndex, toIndex); 437 } 438 439 /** 440 * Reverses the elements of {@code array}. This is equivalent to {@code 441 * Collections.reverse(Doubles.asList(array))}, but is likely to be more efficient. 442 * 443 * @since 23.1 444 */ 445 public static void reverse(double[] array) { 446 checkNotNull(array); 447 reverse(array, 0, array.length); 448 } 449 450 /** 451 * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex} 452 * exclusive. This is equivalent to {@code 453 * Collections.reverse(Doubles.asList(array).subList(fromIndex, toIndex))}, but is likely to be 454 * more efficient. 455 * 456 * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or 457 * {@code toIndex > fromIndex} 458 * @since 23.1 459 */ 460 public static void reverse(double[] array, int fromIndex, int toIndex) { 461 checkNotNull(array); 462 checkPositionIndexes(fromIndex, toIndex, array.length); 463 for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) { 464 double tmp = array[i]; 465 array[i] = array[j]; 466 array[j] = tmp; 467 } 468 } 469 470 /** 471 * Performs a right rotation of {@code array} of "distance" places, so that the first element is 472 * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance 473 * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Bytes.asList(array), 474 * distance)}, but is considerably faster and avoids allocation and garbage collection. 475 * 476 * <p>The provided "distance" may be negative, which will rotate left. 477 * 478 * @since 32.0.0 479 */ 480 public static void rotate(double[] array, int distance) { 481 rotate(array, distance, 0, array.length); 482 } 483 484 /** 485 * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code 486 * toIndex} exclusive. This is equivalent to {@code 487 * Collections.rotate(Bytes.asList(array).subList(fromIndex, toIndex), distance)}, but is 488 * considerably faster and avoids allocations and garbage collection. 489 * 490 * <p>The provided "distance" may be negative, which will rotate left. 491 * 492 * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or 493 * {@code toIndex > fromIndex} 494 * @since 32.0.0 495 */ 496 public static void rotate(double[] array, int distance, int fromIndex, int toIndex) { 497 // See Ints.rotate for more details about possible algorithms here. 498 checkNotNull(array); 499 checkPositionIndexes(fromIndex, toIndex, array.length); 500 if (array.length <= 1) { 501 return; 502 } 503 504 int length = toIndex - fromIndex; 505 // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many 506 // places left to rotate. 507 int m = -distance % length; 508 m = (m < 0) ? m + length : m; 509 // The current index of what will become the first element of the rotated section. 510 int newFirstIndex = m + fromIndex; 511 if (newFirstIndex == fromIndex) { 512 return; 513 } 514 515 reverse(array, fromIndex, newFirstIndex); 516 reverse(array, newFirstIndex, toIndex); 517 reverse(array, fromIndex, toIndex); 518 } 519 520 /** 521 * Returns an array containing each value of {@code collection}, converted to a {@code double} 522 * value in the manner of {@link Number#doubleValue}. 523 * 524 * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}. 525 * Calling this method is as thread-safe as calling that method. 526 * 527 * @param collection a collection of {@code Number} instances 528 * @return an array containing the same values as {@code collection}, in the same order, converted 529 * to primitives 530 * @throws NullPointerException if {@code collection} or any of its elements is null 531 * @since 1.0 (parameter was {@code Collection<Double>} before 12.0) 532 */ 533 public static double[] toArray(Collection<? extends Number> collection) { 534 if (collection instanceof DoubleArrayAsList) { 535 return ((DoubleArrayAsList) collection).toDoubleArray(); 536 } 537 538 Object[] boxedArray = collection.toArray(); 539 int len = boxedArray.length; 540 double[] array = new double[len]; 541 for (int i = 0; i < len; i++) { 542 // checkNotNull for GWT (do not optimize) 543 array[i] = ((Number) checkNotNull(boxedArray[i])).doubleValue(); 544 } 545 return array; 546 } 547 548 /** 549 * Returns a fixed-size list backed by the specified array, similar to {@link 550 * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to 551 * set a value to {@code null} will result in a {@link NullPointerException}. 552 * 553 * <p>The returned list maintains the values, but not the identities, of {@code Double} objects 554 * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for 555 * the returned list is unspecified. 556 * 557 * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN} 558 * is used as a parameter to any of its methods. 559 * 560 * <p>The returned list is serializable. 561 * 562 * <p><b>Note:</b> when possible, you should represent your data as an {@link 563 * ImmutableDoubleArray} instead, which has an {@link ImmutableDoubleArray#asList asList} view. 564 * 565 * @param backingArray the array to back the list 566 * @return a list view of the array 567 */ 568 public static List<Double> asList(double... backingArray) { 569 if (backingArray.length == 0) { 570 return Collections.emptyList(); 571 } 572 return new DoubleArrayAsList(backingArray); 573 } 574 575 @GwtCompatible 576 private static class DoubleArrayAsList extends AbstractList<Double> 577 implements RandomAccess, Serializable { 578 final double[] array; 579 final int start; 580 final int end; 581 582 DoubleArrayAsList(double[] array) { 583 this(array, 0, array.length); 584 } 585 586 DoubleArrayAsList(double[] array, int start, int end) { 587 this.array = array; 588 this.start = start; 589 this.end = end; 590 } 591 592 @Override 593 public int size() { 594 return end - start; 595 } 596 597 @Override 598 public boolean isEmpty() { 599 return false; 600 } 601 602 @Override 603 public Double get(int index) { 604 checkElementIndex(index, size()); 605 return array[start + index]; 606 } 607 608 @Override 609 public Spliterator.OfDouble spliterator() { 610 return Spliterators.spliterator(array, start, end, 0); 611 } 612 613 @Override 614 public boolean contains(@CheckForNull Object target) { 615 // Overridden to prevent a ton of boxing 616 return (target instanceof Double) 617 && Doubles.indexOf(array, (Double) target, start, end) != -1; 618 } 619 620 @Override 621 public int indexOf(@CheckForNull Object target) { 622 // Overridden to prevent a ton of boxing 623 if (target instanceof Double) { 624 int i = Doubles.indexOf(array, (Double) target, start, end); 625 if (i >= 0) { 626 return i - start; 627 } 628 } 629 return -1; 630 } 631 632 @Override 633 public int lastIndexOf(@CheckForNull Object target) { 634 // Overridden to prevent a ton of boxing 635 if (target instanceof Double) { 636 int i = Doubles.lastIndexOf(array, (Double) target, start, end); 637 if (i >= 0) { 638 return i - start; 639 } 640 } 641 return -1; 642 } 643 644 @Override 645 public Double set(int index, Double element) { 646 checkElementIndex(index, size()); 647 double oldValue = array[start + index]; 648 // checkNotNull for GWT (do not optimize) 649 array[start + index] = checkNotNull(element); 650 return oldValue; 651 } 652 653 @Override 654 public List<Double> subList(int fromIndex, int toIndex) { 655 int size = size(); 656 checkPositionIndexes(fromIndex, toIndex, size); 657 if (fromIndex == toIndex) { 658 return Collections.emptyList(); 659 } 660 return new DoubleArrayAsList(array, start + fromIndex, start + toIndex); 661 } 662 663 @Override 664 public boolean equals(@CheckForNull Object object) { 665 if (object == this) { 666 return true; 667 } 668 if (object instanceof DoubleArrayAsList) { 669 DoubleArrayAsList that = (DoubleArrayAsList) object; 670 int size = size(); 671 if (that.size() != size) { 672 return false; 673 } 674 for (int i = 0; i < size; i++) { 675 if (array[start + i] != that.array[that.start + i]) { 676 return false; 677 } 678 } 679 return true; 680 } 681 return super.equals(object); 682 } 683 684 @Override 685 public int hashCode() { 686 int result = 1; 687 for (int i = start; i < end; i++) { 688 result = 31 * result + Doubles.hashCode(array[i]); 689 } 690 return result; 691 } 692 693 @Override 694 public String toString() { 695 StringBuilder builder = new StringBuilder(size() * 12); 696 builder.append('[').append(array[start]); 697 for (int i = start + 1; i < end; i++) { 698 builder.append(", ").append(array[i]); 699 } 700 return builder.append(']').toString(); 701 } 702 703 double[] toDoubleArray() { 704 return Arrays.copyOfRange(array, start, end); 705 } 706 707 private static final long serialVersionUID = 0; 708 } 709 710 /** 711 * This is adapted from the regex suggested by {@link Double#valueOf(String)} for prevalidating 712 * inputs. All valid inputs must pass this regex, but it's semantically fine if not all inputs 713 * that pass this regex are valid -- only a performance hit is incurred, not a semantics bug. 714 */ 715 @J2ktIncompatible @GwtIncompatible // regular expressions 716 static final 717 java.util.regex.Pattern 718 FLOATING_POINT_PATTERN = fpPattern(); 719 720 @GwtIncompatible // regular expressions 721 private static 722 java.util.regex.Pattern 723 fpPattern() { 724 /* 725 * We use # instead of * for possessive quantifiers. This lets us strip them out when building 726 * the regex for RE2 (which doesn't support them) but leave them in when building it for 727 * java.util.regex (where we want them in order to avoid catastrophic backtracking). 728 */ 729 String decimal = "(?:\\d+#(?:\\.\\d*#)?|\\.\\d+#)"; 730 String completeDec = decimal + "(?:[eE][+-]?\\d+#)?[fFdD]?"; 731 String hex = "(?:[0-9a-fA-F]+#(?:\\.[0-9a-fA-F]*#)?|\\.[0-9a-fA-F]+#)"; 732 String completeHex = "0[xX]" + hex + "[pP][+-]?\\d+#[fFdD]?"; 733 String fpPattern = "[+-]?(?:NaN|Infinity|" + completeDec + "|" + completeHex + ")"; 734 fpPattern = 735 fpPattern.replace( 736 "#", 737 "+" 738 ); 739 return 740 java.util.regex.Pattern 741 .compile(fpPattern); 742 } 743 744 /** 745 * Parses the specified string as a double-precision floating point value. The ASCII character 746 * {@code '-'} (<code>'\u002D'</code>) is recognized as the minus sign. 747 * 748 * <p>Unlike {@link Double#parseDouble(String)}, this method returns {@code null} instead of 749 * throwing an exception if parsing fails. Valid inputs are exactly those accepted by {@link 750 * Double#valueOf(String)}, except that leading and trailing whitespace is not permitted. 751 * 752 * <p>This implementation is likely to be faster than {@code Double.parseDouble} if many failures 753 * are expected. 754 * 755 * @param string the string representation of a {@code double} value 756 * @return the floating point value represented by {@code string}, or {@code null} if {@code 757 * string} has a length of zero or cannot be parsed as a {@code double} value 758 * @throws NullPointerException if {@code string} is {@code null} 759 * @since 14.0 760 */ 761 @J2ktIncompatible 762 @GwtIncompatible // regular expressions 763 @CheckForNull 764 public static Double tryParse(String string) { 765 if (FLOATING_POINT_PATTERN.matcher(string).matches()) { 766 // TODO(lowasser): could be potentially optimized, but only with 767 // extensive testing 768 try { 769 return Double.parseDouble(string); 770 } catch (NumberFormatException e) { 771 // Double.parseDouble has changed specs several times, so fall through 772 // gracefully 773 } 774 } 775 return null; 776 } 777}