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.Beta; 026import com.google.common.annotations.GwtCompatible; 027import com.google.common.annotations.GwtIncompatible; 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 @Beta 259 public static double constrainToRange(double value, double min, double max) { 260 // avoid auto-boxing by not using Preconditions.checkArgument(); see Guava issue 3984 261 // Reject NaN by testing for the good case (min <= max) instead of the bad (min > max). 262 if (min <= max) { 263 return Math.min(Math.max(value, min), max); 264 } 265 throw new IllegalArgumentException( 266 lenientFormat("min (%s) must be less than or equal to max (%s)", min, max)); 267 } 268 269 /** 270 * Returns the values from each provided array combined into a single array. For example, {@code 271 * concat(new double[] {a, b}, new double[] {}, new double[] {c}} returns the array {@code {a, b, 272 * c}}. 273 * 274 * @param arrays zero or more {@code double} arrays 275 * @return a single array containing all the values from the source arrays, in order 276 */ 277 public static double[] concat(double[]... arrays) { 278 int length = 0; 279 for (double[] array : arrays) { 280 length += array.length; 281 } 282 double[] result = new double[length]; 283 int pos = 0; 284 for (double[] array : arrays) { 285 System.arraycopy(array, 0, result, pos, array.length); 286 pos += array.length; 287 } 288 return result; 289 } 290 291 private static final class DoubleConverter extends Converter<String, Double> 292 implements Serializable { 293 static final DoubleConverter INSTANCE = new DoubleConverter(); 294 295 @Override 296 protected Double doForward(String value) { 297 return Double.valueOf(value); 298 } 299 300 @Override 301 protected String doBackward(Double value) { 302 return value.toString(); 303 } 304 305 @Override 306 public String toString() { 307 return "Doubles.stringConverter()"; 308 } 309 310 private Object readResolve() { 311 return INSTANCE; 312 } 313 314 private static final long serialVersionUID = 1; 315 } 316 317 /** 318 * Returns a serializable converter object that converts between strings and doubles using {@link 319 * Double#valueOf} and {@link Double#toString()}. 320 * 321 * @since 16.0 322 */ 323 @Beta 324 public static Converter<String, Double> stringConverter() { 325 return DoubleConverter.INSTANCE; 326 } 327 328 /** 329 * Returns an array containing the same values as {@code array}, but guaranteed to be of a 330 * specified minimum length. If {@code array} already has a length of at least {@code minLength}, 331 * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is 332 * returned, containing the values of {@code array}, and zeroes in the remaining places. 333 * 334 * @param array the source array 335 * @param minLength the minimum length the returned array must guarantee 336 * @param padding an extra amount to "grow" the array by if growth is necessary 337 * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative 338 * @return an array containing the values of {@code array}, with guaranteed minimum length {@code 339 * minLength} 340 */ 341 public static double[] ensureCapacity(double[] array, int minLength, int padding) { 342 checkArgument(minLength >= 0, "Invalid minLength: %s", minLength); 343 checkArgument(padding >= 0, "Invalid padding: %s", padding); 344 return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array; 345 } 346 347 /** 348 * Returns a string containing the supplied {@code double} values, converted to strings as 349 * specified by {@link Double#toString(double)}, and separated by {@code separator}. For example, 350 * {@code join("-", 1.0, 2.0, 3.0)} returns the string {@code "1.0-2.0-3.0"}. 351 * 352 * <p>Note that {@link Double#toString(double)} formats {@code double} differently in GWT 353 * sometimes. In the previous example, it returns the string {@code "1-2-3"}. 354 * 355 * @param separator the text that should appear between consecutive values in the resulting string 356 * (but not at the start or end) 357 * @param array an array of {@code double} values, possibly empty 358 */ 359 public static String join(String separator, double... array) { 360 checkNotNull(separator); 361 if (array.length == 0) { 362 return ""; 363 } 364 365 // For pre-sizing a builder, just get the right order of magnitude 366 StringBuilder builder = new StringBuilder(array.length * 12); 367 builder.append(array[0]); 368 for (int i = 1; i < array.length; i++) { 369 builder.append(separator).append(array[i]); 370 } 371 return builder.toString(); 372 } 373 374 /** 375 * Returns a comparator that compares two {@code double} arrays <a 376 * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it 377 * compares, using {@link #compare(double, double)}), the first pair of values that follow any 378 * common prefix, or when one array is a prefix of the other, treats the shorter array as the 379 * lesser. For example, {@code [] < [1.0] < [1.0, 2.0] < [2.0]}. 380 * 381 * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays 382 * support only identity equality), but it is consistent with {@link Arrays#equals(double[], 383 * double[])}. 384 * 385 * @since 2.0 386 */ 387 public static Comparator<double[]> lexicographicalComparator() { 388 return LexicographicalComparator.INSTANCE; 389 } 390 391 private enum LexicographicalComparator implements Comparator<double[]> { 392 INSTANCE; 393 394 @Override 395 public int compare(double[] left, double[] right) { 396 int minLength = Math.min(left.length, right.length); 397 for (int i = 0; i < minLength; i++) { 398 int result = Double.compare(left[i], right[i]); 399 if (result != 0) { 400 return result; 401 } 402 } 403 return left.length - right.length; 404 } 405 406 @Override 407 public String toString() { 408 return "Doubles.lexicographicalComparator()"; 409 } 410 } 411 412 /** 413 * Sorts the elements of {@code array} in descending order. 414 * 415 * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats 416 * all NaN values as equal and 0.0 as greater than -0.0. 417 * 418 * @since 23.1 419 */ 420 public static void sortDescending(double[] array) { 421 checkNotNull(array); 422 sortDescending(array, 0, array.length); 423 } 424 425 /** 426 * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex} 427 * exclusive in descending order. 428 * 429 * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats 430 * all NaN values as equal and 0.0 as greater than -0.0. 431 * 432 * @since 23.1 433 */ 434 public static void sortDescending(double[] array, int fromIndex, int toIndex) { 435 checkNotNull(array); 436 checkPositionIndexes(fromIndex, toIndex, array.length); 437 Arrays.sort(array, fromIndex, toIndex); 438 reverse(array, fromIndex, toIndex); 439 } 440 441 /** 442 * Reverses the elements of {@code array}. This is equivalent to {@code 443 * Collections.reverse(Doubles.asList(array))}, but is likely to be more efficient. 444 * 445 * @since 23.1 446 */ 447 public static void reverse(double[] array) { 448 checkNotNull(array); 449 reverse(array, 0, array.length); 450 } 451 452 /** 453 * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex} 454 * exclusive. This is equivalent to {@code 455 * Collections.reverse(Doubles.asList(array).subList(fromIndex, toIndex))}, but is likely to be 456 * more efficient. 457 * 458 * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or 459 * {@code toIndex > fromIndex} 460 * @since 23.1 461 */ 462 public static void reverse(double[] array, int fromIndex, int toIndex) { 463 checkNotNull(array); 464 checkPositionIndexes(fromIndex, toIndex, array.length); 465 for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) { 466 double tmp = array[i]; 467 array[i] = array[j]; 468 array[j] = tmp; 469 } 470 } 471 472 /** 473 * Performs a right rotation of {@code array} of "distance" places, so that the first element is 474 * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance 475 * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Bytes.asList(array), 476 * distance)}, but is considerably faster and avoids allocation and garbage collection. 477 * 478 * <p>The provided "distance" may be negative, which will rotate left. 479 * 480 * @since NEXT 481 */ 482 public static void rotate(double[] array, int distance) { 483 rotate(array, distance, 0, array.length); 484 } 485 486 /** 487 * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code 488 * toIndex} exclusive. This is equivalent to {@code 489 * Collections.rotate(Bytes.asList(array).subList(fromIndex, toIndex), distance)}, but is 490 * considerably faster and avoids allocations and garbage collection. 491 * 492 * <p>The provided "distance" may be negative, which will rotate left. 493 * 494 * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or 495 * {@code toIndex > fromIndex} 496 * @since NEXT 497 */ 498 public static void rotate(double[] array, int distance, int fromIndex, int toIndex) { 499 // See Ints.rotate for more details about possible algorithms here. 500 checkNotNull(array); 501 checkPositionIndexes(fromIndex, toIndex, array.length); 502 if (array.length <= 1) { 503 return; 504 } 505 506 int length = toIndex - fromIndex; 507 // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many 508 // places left to rotate. 509 int m = -distance % length; 510 m = (m < 0) ? m + length : m; 511 // The current index of what will become the first element of the rotated section. 512 int newFirstIndex = m + fromIndex; 513 if (newFirstIndex == fromIndex) { 514 return; 515 } 516 517 reverse(array, fromIndex, newFirstIndex); 518 reverse(array, newFirstIndex, toIndex); 519 reverse(array, fromIndex, toIndex); 520 } 521 522 /** 523 * Returns an array containing each value of {@code collection}, converted to a {@code double} 524 * value in the manner of {@link Number#doubleValue}. 525 * 526 * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}. 527 * Calling this method is as thread-safe as calling that method. 528 * 529 * @param collection a collection of {@code Number} instances 530 * @return an array containing the same values as {@code collection}, in the same order, converted 531 * to primitives 532 * @throws NullPointerException if {@code collection} or any of its elements is null 533 * @since 1.0 (parameter was {@code Collection<Double>} before 12.0) 534 */ 535 public static double[] toArray(Collection<? extends Number> collection) { 536 if (collection instanceof DoubleArrayAsList) { 537 return ((DoubleArrayAsList) collection).toDoubleArray(); 538 } 539 540 Object[] boxedArray = collection.toArray(); 541 int len = boxedArray.length; 542 double[] array = new double[len]; 543 for (int i = 0; i < len; i++) { 544 // checkNotNull for GWT (do not optimize) 545 array[i] = ((Number) checkNotNull(boxedArray[i])).doubleValue(); 546 } 547 return array; 548 } 549 550 /** 551 * Returns a fixed-size list backed by the specified array, similar to {@link 552 * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to 553 * set a value to {@code null} will result in a {@link NullPointerException}. 554 * 555 * <p>The returned list maintains the values, but not the identities, of {@code Double} objects 556 * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for 557 * the returned list is unspecified. 558 * 559 * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN} 560 * is used as a parameter to any of its methods. 561 * 562 * <p>The returned list is serializable. 563 * 564 * <p><b>Note:</b> when possible, you should represent your data as an {@link 565 * ImmutableDoubleArray} instead, which has an {@link ImmutableDoubleArray#asList asList} view. 566 * 567 * @param backingArray the array to back the list 568 * @return a list view of the array 569 */ 570 public static List<Double> asList(double... backingArray) { 571 if (backingArray.length == 0) { 572 return Collections.emptyList(); 573 } 574 return new DoubleArrayAsList(backingArray); 575 } 576 577 @GwtCompatible 578 private static class DoubleArrayAsList extends AbstractList<Double> 579 implements RandomAccess, Serializable { 580 final double[] array; 581 final int start; 582 final int end; 583 584 DoubleArrayAsList(double[] array) { 585 this(array, 0, array.length); 586 } 587 588 DoubleArrayAsList(double[] array, int start, int end) { 589 this.array = array; 590 this.start = start; 591 this.end = end; 592 } 593 594 @Override 595 public int size() { 596 return end - start; 597 } 598 599 @Override 600 public boolean isEmpty() { 601 return false; 602 } 603 604 @Override 605 public Double get(int index) { 606 checkElementIndex(index, size()); 607 return array[start + index]; 608 } 609 610 @Override 611 public Spliterator.OfDouble spliterator() { 612 return Spliterators.spliterator(array, start, end, 0); 613 } 614 615 @Override 616 public boolean contains(@CheckForNull Object target) { 617 // Overridden to prevent a ton of boxing 618 return (target instanceof Double) 619 && Doubles.indexOf(array, (Double) target, start, end) != -1; 620 } 621 622 @Override 623 public int indexOf(@CheckForNull Object target) { 624 // Overridden to prevent a ton of boxing 625 if (target instanceof Double) { 626 int i = Doubles.indexOf(array, (Double) target, start, end); 627 if (i >= 0) { 628 return i - start; 629 } 630 } 631 return -1; 632 } 633 634 @Override 635 public int lastIndexOf(@CheckForNull Object target) { 636 // Overridden to prevent a ton of boxing 637 if (target instanceof Double) { 638 int i = Doubles.lastIndexOf(array, (Double) target, start, end); 639 if (i >= 0) { 640 return i - start; 641 } 642 } 643 return -1; 644 } 645 646 @Override 647 public Double set(int index, Double element) { 648 checkElementIndex(index, size()); 649 double oldValue = array[start + index]; 650 // checkNotNull for GWT (do not optimize) 651 array[start + index] = checkNotNull(element); 652 return oldValue; 653 } 654 655 @Override 656 public List<Double> subList(int fromIndex, int toIndex) { 657 int size = size(); 658 checkPositionIndexes(fromIndex, toIndex, size); 659 if (fromIndex == toIndex) { 660 return Collections.emptyList(); 661 } 662 return new DoubleArrayAsList(array, start + fromIndex, start + toIndex); 663 } 664 665 @Override 666 public boolean equals(@CheckForNull Object object) { 667 if (object == this) { 668 return true; 669 } 670 if (object instanceof DoubleArrayAsList) { 671 DoubleArrayAsList that = (DoubleArrayAsList) object; 672 int size = size(); 673 if (that.size() != size) { 674 return false; 675 } 676 for (int i = 0; i < size; i++) { 677 if (array[start + i] != that.array[that.start + i]) { 678 return false; 679 } 680 } 681 return true; 682 } 683 return super.equals(object); 684 } 685 686 @Override 687 public int hashCode() { 688 int result = 1; 689 for (int i = start; i < end; i++) { 690 result = 31 * result + Doubles.hashCode(array[i]); 691 } 692 return result; 693 } 694 695 @Override 696 public String toString() { 697 StringBuilder builder = new StringBuilder(size() * 12); 698 builder.append('[').append(array[start]); 699 for (int i = start + 1; i < end; i++) { 700 builder.append(", ").append(array[i]); 701 } 702 return builder.append(']').toString(); 703 } 704 705 double[] toDoubleArray() { 706 return Arrays.copyOfRange(array, start, end); 707 } 708 709 private static final long serialVersionUID = 0; 710 } 711 712 /** 713 * This is adapted from the regex suggested by {@link Double#valueOf(String)} for prevalidating 714 * inputs. All valid inputs must pass this regex, but it's semantically fine if not all inputs 715 * that pass this regex are valid -- only a performance hit is incurred, not a semantics bug. 716 */ 717 @GwtIncompatible // regular expressions 718 static final 719 java.util.regex.Pattern 720 FLOATING_POINT_PATTERN = fpPattern(); 721 722 @GwtIncompatible // regular expressions 723 private static 724 java.util.regex.Pattern 725 fpPattern() { 726 /* 727 * We use # instead of * for possessive quantifiers. This lets us strip them out when building 728 * the regex for RE2 (which doesn't support them) but leave them in when building it for 729 * java.util.regex (where we want them in order to avoid catastrophic backtracking). 730 */ 731 String decimal = "(?:\\d+#(?:\\.\\d*#)?|\\.\\d+#)"; 732 String completeDec = decimal + "(?:[eE][+-]?\\d+#)?[fFdD]?"; 733 String hex = "(?:[0-9a-fA-F]+#(?:\\.[0-9a-fA-F]*#)?|\\.[0-9a-fA-F]+#)"; 734 String completeHex = "0[xX]" + hex + "[pP][+-]?\\d+#[fFdD]?"; 735 String fpPattern = "[+-]?(?:NaN|Infinity|" + completeDec + "|" + completeHex + ")"; 736 fpPattern = 737 fpPattern.replace( 738 "#", 739 "+" 740 ); 741 return 742 java.util.regex.Pattern 743 .compile(fpPattern); 744 } 745 746 /** 747 * Parses the specified string as a double-precision floating point value. The ASCII character 748 * {@code '-'} (<code>'\u002D'</code>) is recognized as the minus sign. 749 * 750 * <p>Unlike {@link Double#parseDouble(String)}, this method returns {@code null} instead of 751 * throwing an exception if parsing fails. Valid inputs are exactly those accepted by {@link 752 * Double#valueOf(String)}, except that leading and trailing whitespace is not permitted. 753 * 754 * <p>This implementation is likely to be faster than {@code Double.parseDouble} if many failures 755 * are expected. 756 * 757 * @param string the string representation of a {@code double} value 758 * @return the floating point value represented by {@code string}, or {@code null} if {@code 759 * string} has a length of zero or cannot be parsed as a {@code double} value 760 * @throws NullPointerException if {@code string} is {@code null} 761 * @since 14.0 762 */ 763 @Beta 764 @GwtIncompatible // regular expressions 765 @CheckForNull 766 public static Double tryParse(String string) { 767 if (FLOATING_POINT_PATTERN.matcher(string).matches()) { 768 // TODO(lowasser): could be potentially optimized, but only with 769 // extensive testing 770 try { 771 return Double.parseDouble(string); 772 } catch (NumberFormatException e) { 773 // Double.parseDouble has changed specs several times, so fall through 774 // gracefully 775 } 776 } 777 return null; 778 } 779}