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