001 /*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.primitives;
018
019 import static com.google.common.base.Preconditions.checkArgument;
020 import static com.google.common.base.Preconditions.checkElementIndex;
021 import static com.google.common.base.Preconditions.checkNotNull;
022 import static com.google.common.base.Preconditions.checkPositionIndexes;
023 import static java.lang.Double.NEGATIVE_INFINITY;
024 import static java.lang.Double.POSITIVE_INFINITY;
025
026 import com.google.common.annotations.GwtCompatible;
027
028 import java.io.Serializable;
029 import java.util.AbstractList;
030 import java.util.Arrays;
031 import java.util.Collection;
032 import java.util.Collections;
033 import java.util.Comparator;
034 import java.util.List;
035 import java.util.RandomAccess;
036
037 /**
038 * Static utility methods pertaining to {@code double} primitives, that are not
039 * already found in either {@link Double} or {@link Arrays}.
040 *
041 * @author Kevin Bourrillion
042 * @since 1.0
043 */
044 @GwtCompatible
045 public final class Doubles {
046 private Doubles() {}
047
048 /**
049 * The number of bytes required to represent a primitive {@code double}
050 * value.
051 *
052 * @since 10.0
053 */
054 public static final int BYTES = Double.SIZE / Byte.SIZE;
055
056 /**
057 * Returns a hash code for {@code value}; equal to the result of invoking
058 * {@code ((Double) value).hashCode()}.
059 *
060 * @param value a primitive {@code double} value
061 * @return a hash code for the value
062 */
063 public static int hashCode(double value) {
064 return ((Double) value).hashCode();
065 // TODO(kevinb): do it this way when we can (GWT problem):
066 // long bits = Double.doubleToLongBits(value);
067 // return (int)(bits ^ (bits >>> 32));
068 }
069
070 /**
071 * Compares the two specified {@code double} values. The sign of the value
072 * returned is the same as that of <code>((Double) a).{@linkplain
073 * Double#compareTo compareTo}(b)</code>. As with that method, {@code NaN} is
074 * treated as greater than all other values, and {@code 0.0 > -0.0}.
075 *
076 * @param a the first {@code double} to compare
077 * @param b the second {@code double} to compare
078 * @return a negative value if {@code a} is less than {@code b}; a positive
079 * value if {@code a} is greater than {@code b}; or zero if they are equal
080 */
081 public static int compare(double a, double b) {
082 return Double.compare(a, b);
083 }
084
085 /**
086 * Returns {@code true} if {@code value} represents a real number. This is
087 * equivalent to, but not necessarily implemented as,
088 * {@code !(Double.isInfinite(value) || Double.isNaN(value))}.
089 *
090 * @since 10.0
091 */
092 public static boolean isFinite(double value) {
093 return NEGATIVE_INFINITY < value & value < POSITIVE_INFINITY;
094 }
095
096 /**
097 * Returns {@code true} if {@code target} is present as an element anywhere in
098 * {@code array}. Note that this always returns {@code false} when {@code
099 * target} is {@code NaN}.
100 *
101 * @param array an array of {@code double} values, possibly empty
102 * @param target a primitive {@code double} value
103 * @return {@code true} if {@code array[i] == target} for some value of {@code
104 * i}
105 */
106 public static boolean contains(double[] array, double target) {
107 for (double value : array) {
108 if (value == target) {
109 return true;
110 }
111 }
112 return false;
113 }
114
115 /**
116 * Returns the index of the first appearance of the value {@code target} in
117 * {@code array}. Note that this always returns {@code -1} when {@code target}
118 * is {@code NaN}.
119 *
120 * @param array an array of {@code double} values, possibly empty
121 * @param target a primitive {@code double} value
122 * @return the least index {@code i} for which {@code array[i] == target}, or
123 * {@code -1} if no such index exists.
124 */
125 public static int indexOf(double[] array, double target) {
126 return indexOf(array, target, 0, array.length);
127 }
128
129 // TODO(kevinb): consider making this public
130 private static int indexOf(
131 double[] array, double target, int start, int end) {
132 for (int i = start; i < end; i++) {
133 if (array[i] == target) {
134 return i;
135 }
136 }
137 return -1;
138 }
139
140 /**
141 * Returns the start position of the first occurrence of the specified {@code
142 * target} within {@code array}, or {@code -1} if there is no such occurrence.
143 *
144 * <p>More formally, returns the lowest index {@code i} such that {@code
145 * java.util.Arrays.copyOfRange(array, i, i + target.length)} contains exactly
146 * the same elements as {@code target}.
147 *
148 * <p>Note that this always returns {@code -1} when {@code target} contains
149 * {@code NaN}.
150 *
151 * @param array the array to search for the sequence {@code target}
152 * @param target the array to search for as a sub-sequence of {@code array}
153 */
154 public static int indexOf(double[] array, double[] target) {
155 checkNotNull(array, "array");
156 checkNotNull(target, "target");
157 if (target.length == 0) {
158 return 0;
159 }
160
161 outer:
162 for (int i = 0; i < array.length - target.length + 1; i++) {
163 for (int j = 0; j < target.length; j++) {
164 if (array[i + j] != target[j]) {
165 continue outer;
166 }
167 }
168 return i;
169 }
170 return -1;
171 }
172
173 /**
174 * Returns the index of the last appearance of the value {@code target} in
175 * {@code array}. Note that this always returns {@code -1} when {@code target}
176 * is {@code NaN}.
177 *
178 * @param array an array of {@code double} values, possibly empty
179 * @param target a primitive {@code double} value
180 * @return the greatest index {@code i} for which {@code array[i] == target},
181 * or {@code -1} if no such index exists.
182 */
183 public static int lastIndexOf(double[] array, double target) {
184 return lastIndexOf(array, target, 0, array.length);
185 }
186
187 // TODO(kevinb): consider making this public
188 private static int lastIndexOf(
189 double[] array, double target, int start, int end) {
190 for (int i = end - 1; i >= start; i--) {
191 if (array[i] == target) {
192 return i;
193 }
194 }
195 return -1;
196 }
197
198 /**
199 * Returns the least value present in {@code array}, using the same rules of
200 * comparison as {@link Math#min(double, double)}.
201 *
202 * @param array a <i>nonempty</i> array of {@code double} values
203 * @return the value present in {@code array} that is less than or equal to
204 * every other value in the array
205 * @throws IllegalArgumentException if {@code array} is empty
206 */
207 public static double min(double... array) {
208 checkArgument(array.length > 0);
209 double min = array[0];
210 for (int i = 1; i < array.length; i++) {
211 min = Math.min(min, array[i]);
212 }
213 return min;
214 }
215
216 /**
217 * Returns the greatest value present in {@code array}, using the same rules
218 * of comparison as {@link Math#max(double, double)}.
219 *
220 * @param array a <i>nonempty</i> array of {@code double} values
221 * @return the value present in {@code array} that is greater than or equal to
222 * every other value in the array
223 * @throws IllegalArgumentException if {@code array} is empty
224 */
225 public static double max(double... array) {
226 checkArgument(array.length > 0);
227 double max = array[0];
228 for (int i = 1; i < array.length; i++) {
229 max = Math.max(max, array[i]);
230 }
231 return max;
232 }
233
234 /**
235 * Returns the values from each provided array combined into a single array.
236 * For example, {@code concat(new double[] {a, b}, new double[] {}, new
237 * double[] {c}} returns the array {@code {a, b, c}}.
238 *
239 * @param arrays zero or more {@code double} arrays
240 * @return a single array containing all the values from the source arrays, in
241 * order
242 */
243 public static double[] concat(double[]... arrays) {
244 int length = 0;
245 for (double[] array : arrays) {
246 length += array.length;
247 }
248 double[] result = new double[length];
249 int pos = 0;
250 for (double[] array : arrays) {
251 System.arraycopy(array, 0, result, pos, array.length);
252 pos += array.length;
253 }
254 return result;
255 }
256
257 /**
258 * Returns an array containing the same values as {@code array}, but
259 * guaranteed to be of a specified minimum length. If {@code array} already
260 * has a length of at least {@code minLength}, it is returned directly.
261 * Otherwise, a new array of size {@code minLength + padding} is returned,
262 * containing the values of {@code array}, and zeroes in the remaining places.
263 *
264 * @param array the source array
265 * @param minLength the minimum length the returned array must guarantee
266 * @param padding an extra amount to "grow" the array by if growth is
267 * necessary
268 * @throws IllegalArgumentException if {@code minLength} or {@code padding} is
269 * negative
270 * @return an array containing the values of {@code array}, with guaranteed
271 * minimum length {@code minLength}
272 */
273 public static double[] ensureCapacity(
274 double[] array, int minLength, int padding) {
275 checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
276 checkArgument(padding >= 0, "Invalid padding: %s", padding);
277 return (array.length < minLength)
278 ? copyOf(array, minLength + padding)
279 : array;
280 }
281
282 // Arrays.copyOf() requires Java 6
283 private static double[] copyOf(double[] original, int length) {
284 double[] copy = new double[length];
285 System.arraycopy(original, 0, copy, 0, Math.min(original.length, length));
286 return copy;
287 }
288
289 /**
290 * Returns a string containing the supplied {@code double} values, converted
291 * to strings as specified by {@link Double#toString(double)}, and separated
292 * by {@code separator}. For example, {@code join("-", 1.0, 2.0, 3.0)} returns
293 * the string {@code "1.0-2.0-3.0"}.
294 *
295 * <p>Note that {@link Double#toString(double)} formats {@code double}
296 * differently in GWT sometimes. In the previous example, it returns the string
297 * {@code "1-2-3"}.
298 *
299 * @param separator the text that should appear between consecutive values in
300 * the resulting string (but not at the start or end)
301 * @param array an array of {@code double} values, possibly empty
302 */
303 public static String join(String separator, double... array) {
304 checkNotNull(separator);
305 if (array.length == 0) {
306 return "";
307 }
308
309 // For pre-sizing a builder, just get the right order of magnitude
310 StringBuilder builder = new StringBuilder(array.length * 12);
311 builder.append(array[0]);
312 for (int i = 1; i < array.length; i++) {
313 builder.append(separator).append(array[i]);
314 }
315 return builder.toString();
316 }
317
318 /**
319 * Returns a comparator that compares two {@code double} arrays
320 * lexicographically. That is, it compares, using {@link
321 * #compare(double, double)}), the first pair of values that follow any
322 * common prefix, or when one array is a prefix of the other, treats the
323 * shorter array as the lesser. For example,
324 * {@code [] < [1.0] < [1.0, 2.0] < [2.0]}.
325 *
326 * <p>The returned comparator is inconsistent with {@link
327 * Object#equals(Object)} (since arrays support only identity equality), but
328 * it is consistent with {@link Arrays#equals(double[], double[])}.
329 *
330 * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
331 * Lexicographical order article at Wikipedia</a>
332 * @since 2.0
333 */
334 public static Comparator<double[]> lexicographicalComparator() {
335 return LexicographicalComparator.INSTANCE;
336 }
337
338 private enum LexicographicalComparator implements Comparator<double[]> {
339 INSTANCE;
340
341 @Override
342 public int compare(double[] left, double[] right) {
343 int minLength = Math.min(left.length, right.length);
344 for (int i = 0; i < minLength; i++) {
345 int result = Doubles.compare(left[i], right[i]);
346 if (result != 0) {
347 return result;
348 }
349 }
350 return left.length - right.length;
351 }
352 }
353
354 /**
355 * Copies a collection of {@code Double} instances into a new array of
356 * primitive {@code double} values.
357 *
358 * <p>Elements are copied from the argument collection as if by {@code
359 * collection.toArray()}. Calling this method is as thread-safe as calling
360 * that method.
361 *
362 * @param collection a collection of {@code Double} objects
363 * @return an array containing the same values as {@code collection}, in the
364 * same order, converted to primitives
365 * @throws NullPointerException if {@code collection} or any of its elements
366 * is null
367 */
368 public static double[] toArray(Collection<Double> collection) {
369 if (collection instanceof DoubleArrayAsList) {
370 return ((DoubleArrayAsList) collection).toDoubleArray();
371 }
372
373 Object[] boxedArray = collection.toArray();
374 int len = boxedArray.length;
375 double[] array = new double[len];
376 for (int i = 0; i < len; i++) {
377 // checkNotNull for GWT (do not optimize)
378 array[i] = (Double) checkNotNull(boxedArray[i]);
379 }
380 return array;
381 }
382
383 /**
384 * Returns a fixed-size list backed by the specified array, similar to {@link
385 * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)},
386 * but any attempt to set a value to {@code null} will result in a {@link
387 * NullPointerException}.
388 *
389 * <p>The returned list maintains the values, but not the identities, of
390 * {@code Double} objects written to or read from it. For example, whether
391 * {@code list.get(0) == list.get(0)} is true for the returned list is
392 * unspecified.
393 *
394 * <p>The returned list may have unexpected behavior if it contains {@code
395 * NaN}, or if {@code NaN} is used as a parameter to any of its methods.
396 *
397 * @param backingArray the array to back the list
398 * @return a list view of the array
399 */
400 public static List<Double> asList(double... backingArray) {
401 if (backingArray.length == 0) {
402 return Collections.emptyList();
403 }
404 return new DoubleArrayAsList(backingArray);
405 }
406
407 @GwtCompatible
408 private static class DoubleArrayAsList extends AbstractList<Double>
409 implements RandomAccess, Serializable {
410 final double[] array;
411 final int start;
412 final int end;
413
414 DoubleArrayAsList(double[] array) {
415 this(array, 0, array.length);
416 }
417
418 DoubleArrayAsList(double[] array, int start, int end) {
419 this.array = array;
420 this.start = start;
421 this.end = end;
422 }
423
424 @Override public int size() {
425 return end - start;
426 }
427
428 @Override public boolean isEmpty() {
429 return false;
430 }
431
432 @Override public Double get(int index) {
433 checkElementIndex(index, size());
434 return array[start + index];
435 }
436
437 @Override public boolean contains(Object target) {
438 // Overridden to prevent a ton of boxing
439 return (target instanceof Double)
440 && Doubles.indexOf(array, (Double) target, start, end) != -1;
441 }
442
443 @Override public int indexOf(Object target) {
444 // Overridden to prevent a ton of boxing
445 if (target instanceof Double) {
446 int i = Doubles.indexOf(array, (Double) target, start, end);
447 if (i >= 0) {
448 return i - start;
449 }
450 }
451 return -1;
452 }
453
454 @Override public int lastIndexOf(Object target) {
455 // Overridden to prevent a ton of boxing
456 if (target instanceof Double) {
457 int i = Doubles.lastIndexOf(array, (Double) target, start, end);
458 if (i >= 0) {
459 return i - start;
460 }
461 }
462 return -1;
463 }
464
465 @Override public Double set(int index, Double element) {
466 checkElementIndex(index, size());
467 double oldValue = array[start + index];
468 array[start + index] = checkNotNull(element); // checkNotNull for GWT (do not optimize)
469 return oldValue;
470 }
471
472 @Override public List<Double> subList(int fromIndex, int toIndex) {
473 int size = size();
474 checkPositionIndexes(fromIndex, toIndex, size);
475 if (fromIndex == toIndex) {
476 return Collections.emptyList();
477 }
478 return new DoubleArrayAsList(array, start + fromIndex, start + toIndex);
479 }
480
481 @Override public boolean equals(Object object) {
482 if (object == this) {
483 return true;
484 }
485 if (object instanceof DoubleArrayAsList) {
486 DoubleArrayAsList that = (DoubleArrayAsList) object;
487 int size = size();
488 if (that.size() != size) {
489 return false;
490 }
491 for (int i = 0; i < size; i++) {
492 if (array[start + i] != that.array[that.start + i]) {
493 return false;
494 }
495 }
496 return true;
497 }
498 return super.equals(object);
499 }
500
501 @Override public int hashCode() {
502 int result = 1;
503 for (int i = start; i < end; i++) {
504 result = 31 * result + Doubles.hashCode(array[i]);
505 }
506 return result;
507 }
508
509 @Override public String toString() {
510 StringBuilder builder = new StringBuilder(size() * 12);
511 builder.append('[').append(array[start]);
512 for (int i = start + 1; i < end; i++) {
513 builder.append(", ").append(array[i]);
514 }
515 return builder.append(']').toString();
516 }
517
518 double[] toDoubleArray() {
519 // Arrays.copyOfRange() requires Java 6
520 int size = size();
521 double[] result = new double[size];
522 System.arraycopy(array, start, result, 0, size);
523 return result;
524 }
525
526 private static final long serialVersionUID = 0;
527 }
528 }