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16 package org.apache.commons.math.util;
17
18 import java.io.Serializable;
19
20 /***
21 * <p>
22 * A variable length {@link DoubleArray} implementation that automatically
23 * handles expanding and contracting its internal storage array as elements
24 * are added and removed.
25 * </p>
26 * <p>
27 * The internal storage array starts with capacity determined by the
28 * <code>initialCapacity</code> property, which can be set by the constructor.
29 * The default initial capacity is 16. Adding elements using
30 * {@link #addElement(double)} appends elements to the end of the array. When
31 * there are no open entries at the end of the internal storage array, the
32 * array is expanded. The size of the expanded array depends on the
33 * <code>expansionMode</code> and <code>expansionFactor</code> properties.
34 * The <code>expansionMode</code> determines whether the size of the array is
35 * multiplied by the <code>expansionFactor</code> (MULTIPLICATIVE_MODE) or if
36 * the expansion is additive (ADDITIVE_MODE -- <code>expansionFactor</code>
37 * storage locations added). The default <code>expansionMode</code> is
38 * MULTIPLICATIVE_MODE and the default <code>expansionFactor</code>
39 * is 2.0.
40 * </p>
41 * <p>
42 * The {@link #addElementRolling(double)} method adds a new element to the end
43 * of the internal storage array and adjusts the "usable window" of the
44 * internal array forward by one position (effectively making what was the
45 * second element the first, and so on). Repeated activations of this method
46 * (or activation of {@link #discardFrontElements(int)}) will effectively orphan
47 * the storage locations at the beginning of the internal storage array. To
48 * reclaim this storage, each time one of these methods is activated, the size
49 * of the internal storage array is compared to the number of addressable
50 * elements (the <code>numElements</code> property) and if the difference
51 * is too large, the internal array is contracted to size
52 * <code>numElements + 1.</code> The determination of when the internal
53 * storage array is "too large" depends on the <code>expansionMode</code> and
54 * <code>contractionFactor</code> properties. If the <code>expansionMode</code>
55 * is <code>MULTIPLICATIVE_MODE</code>, contraction is triggered when the
56 * ratio between storage array length and <code>numElements</code> exceeds
57 * <code>contractionFactor.</code> If the <code>expansionMode</code>
58 * is <code>ADDITIVE_MODE,</code> the number of excess storage locations
59 * is compared to <code>contractionFactor.</code>
60 * </p>
61 * <p>
62 * To avoid cycles of expansions and contractions, the
63 * <code>expansionFactor</code> must not exceed the
64 * <code>contractionFactor.</code> Constructors and mutators for both of these
65 * properties enforce this requirement, throwing IllegalArgumentException if it
66 * is violated.
67 * </p>
68 * <p>
69 * @version $Revision: 1.2 $ $Date: 2004/06/23 16:26:16 $
70 */
71 public class ResizableDoubleArray implements DoubleArray, Serializable {
72
73 /*** Serializable version identifier */
74 static final long serialVersionUID = -3485529955529426875L;
75
76 /*** additive expansion mode */
77 public static final int ADDITIVE_MODE = 1;
78
79 /*** multiplicative expansion mode */
80 public static final int MULTIPLICATIVE_MODE = 0;
81
82 /***
83 * The contraction criteria determines when the internal array will be
84 * contracted to fit the number of elements contained in the element
85 * array + 1.
86 */
87 protected float contractionCriteria = 2.5f;
88
89 /***
90 * The expansion factor of the array. When the array needs to be expanded,
91 * the new array size will be
92 * <code>internalArray.length * expansionFactor</code>
93 * if <code>expansionMode</code> is set to MULTIPLICATIVE_MODE, or
94 * <code>internalArray.length + expansionFactor</code> if
95 * <code>expansionMode</code> is set to ADDITIVE_MODE.
96 */
97 protected float expansionFactor = 2.0f;
98
99 /***
100 * Determines whether array expansion by <code>expansionFactor</code>
101 * is additive or multiplicative.
102 */
103 protected int expansionMode = MULTIPLICATIVE_MODE;
104
105 /***
106 * The initial capacity of the array. Initial capacity is not exposed as a
107 * property as it is only meaningful when passed to a constructor.
108 */
109 protected int initialCapacity = 16;
110
111 /***
112 * The internal storage array.
113 */
114 protected double[] internalArray;
115
116 /***
117 * The number of addressable elements in the array. Note that this
118 * has nothing to do with the length of the internal storage array.
119 */
120 protected int numElements = 0;
121
122 /***
123 * The position of the first addressable element in the internal storage
124 * array. The addressable elements in the array are <code>
125 * internalArray[startIndex],...,internalArray[startIndex + numElements -1]
126 * </code>
127 */
128 protected int startIndex = 0;
129
130 /***
131 * Create a ResizableArray with default properties.
132 * <ul>
133 * <li><code>initialCapacity = 16</code></li>
134 * <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
135 * <li><code>expansionFactor = 2.5</code></li>
136 * <li><code>contractionFactor = 2.0</code></li>
137 * </ul>
138 */
139 public ResizableDoubleArray() {
140 internalArray = new double[initialCapacity];
141 }
142
143 /***
144 * Create a ResizableArray with the specified initial capacity. Other
145 * properties take default values:
146 * <ul>
147 * <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
148 * <li><code>expansionFactor = 2.5</code></li>
149 * <li><code>contractionFactor = 2.0</code></li>
150 * </ul>
151 * @param initialCapacity The initial size of the internal storage array
152 * @throws IllegalArgumentException if initialCapacity is not > 0
153 */
154 public ResizableDoubleArray(int initialCapacity) {
155 setInitialCapacity(initialCapacity);
156 internalArray = new double[this.initialCapacity];
157 }
158
159 /***
160 * <p>
161 * Create a ResizableArray with the specified initial capacity
162 * and expansion factor. The remaining properties take default
163 * values:
164 * <ul>
165 * <li><code>expansionMode = MULTIPLICATIVE_MODE</code></li>
166 * <li><code>contractionFactor = 0.5 + expansionFactor</code></li>
167 * </ul></p>
168 * <p>
169 * Throws IllegalArgumentException if the following conditions are
170 * not met:
171 * <ul>
172 * <li><code>initialCapacity > 0</code></li>
173 * <li><code>expansionFactor > 1</code></li>
174 * </ul></p>
175 *
176 * @param initialCapacity The initial size of the internal storage array
177 * @param expansionFactor the array will be expanded based on this
178 * parameter
179 * @throws IllegalArgumentException if parameters are not valid
180 */
181 public ResizableDoubleArray(int initialCapacity, float expansionFactor) {
182 this.expansionFactor = expansionFactor;
183 setInitialCapacity(initialCapacity);
184 internalArray = new double[initialCapacity];
185 setContractionCriteria(expansionFactor +0.5f);
186 }
187
188 /***
189 * <p>
190 * Create a ResizableArray with the specified initialCapacity,
191 * expansionFactor, and contractionCriteria. The <code>expansionMode</code>
192 * will default to <code>MULTIPLICATIVE_MODE.</code></p>
193 * <p>
194 * Throws IllegalArgumentException if the following conditions are
195 * not met:
196 * <ul>
197 * <li><code>initialCapacity > 0</code></li>
198 * <li><code>expansionFactor > 1</code></li>
199 * <li><code>contractionFactor >= expansionFactor</code></li>
200 * </ul></p>
201 * @param initialCapacity The initial size of the internal storage array
202 * @param expansionFactor the array will be expanded based on this
203 * parameter
204 * @param contractionCriteria The contraction Criteria.
205 * @throws IllegalArgumentException if parameters are not valid
206 */
207 public ResizableDoubleArray(int initialCapacity, float expansionFactor,
208 float contractionCriteria) {
209 this.expansionFactor = expansionFactor;
210 setContractionCriteria(contractionCriteria);
211 setInitialCapacity(initialCapacity);
212 internalArray = new double[initialCapacity];
213 }
214
215 /***
216 * <p>
217 * Create a ResizableArray with the specified properties.</p>
218 * <p>
219 * Throws IllegalArgumentException if the following conditions are
220 * not met:
221 * <ul>
222 * <li><code>initialCapacity > 0</code></li>
223 * <li><code>expansionFactor > 1</code></li>
224 * <li><code>contractionFactor >= expansionFactor</code></li>
225 * <li><code>expansionMode in {MULTIPLICATIVE_MODE, ADDITIVE_MODE}</code>
226 * </li>
227 * </ul></p>
228 *
229 * @param initialCapacity the initial size of the internal storage array
230 * @param expansionFactor the array will be expanded based on this
231 * parameter
232 * @param contractionCriteria the contraction Criteria
233 * @param expansionMode the expansion mode
234 * @throws IllegalArgumentException if parameters are not valid
235 */
236 public ResizableDoubleArray(int initialCapacity, float expansionFactor,
237 float contractionCriteria, int expansionMode) {
238 this.expansionFactor = expansionFactor;
239 setContractionCriteria(contractionCriteria);
240 setInitialCapacity(initialCapacity);
241 setExpansionMode(expansionMode);
242 internalArray = new double[initialCapacity];
243 }
244
245 /***
246 * Adds an element to the end of this expandable array.
247 *
248 * @param value to be added to end of array
249 */
250 public synchronized void addElement(double value) {
251 numElements++;
252 if ((startIndex + numElements) > internalArray.length) {
253 expand();
254 }
255 internalArray[startIndex + (numElements - 1)] = value;
256 if (shouldContract()) {
257 contract();
258 }
259 }
260
261 /***
262 * <p>
263 * Adds an element to the end of the array and removes the first
264 * element in the array. Returns the discarded first element.
265 * The effect is similar to a push operation in a FIFO queue.
266 * </p>
267 * <p>
268 * Example: If the array contains the elements 1, 2, 3, 4 (in that order)
269 * and addElementRolling(5) is invoked, the result is an array containing
270 * the entries 2, 3, 4, 5 and the value returned is 1.
271 * </p>
272 *
273 * @param value the value to be added to the array
274 * @return the value which has been discarded or "pushed" out of the array
275 * by this rolling insert
276 */
277 public synchronized double addElementRolling(double value) {
278 double discarded = internalArray[startIndex];
279
280 if ((startIndex + (numElements + 1)) > internalArray.length) {
281 expand();
282 }
283
284 startIndex += 1;
285
286
287 internalArray[startIndex + (numElements - 1)] = value;
288
289
290 if (shouldContract()) {
291 contract();
292 }
293 return discarded;
294 }
295
296 /***
297 * Checks the expansion factor and the contraction criteria and throws an
298 * IllegalArgumentException if the contractionCriteria is less than the
299 * expansionCriteria
300 *
301 * @param expansionFactor factor to be checked
302 * @param contractionCritera critera to be checked
303 * @throws IllegalArgumentException if the contractionCriteria is less than
304 * the expansionCriteria.
305 */
306 protected void checkContractExpand(
307 float contractionCritera,
308 float expansionFactor) {
309
310 if (contractionCritera < expansionFactor) {
311 String msg =
312 "Contraction criteria can never be smaller than " +
313 "the expansion factor. This would lead to a never " +
314 "ending loop of expansion and contraction as a newly " +
315 "expanded internal storage array would immediately " +
316 "satisfy the criteria for contraction";
317 throw new IllegalArgumentException(msg);
318 }
319
320 if (contractionCriteria <= 1.0) {
321 String msg =
322 "The contraction criteria must be a number larger " +
323 "than one. If the contractionCriteria is less than or " +
324 "equal to one an endless loop of contraction and " +
325 "expansion would ensue as an internalArray.length " +
326 "== numElements would satisfy the contraction criteria";
327 throw new IllegalArgumentException(msg);
328 }
329
330 if (expansionFactor <= 1.0) {
331 String msg =
332 "The expansion factor must be a number greater than 1.0";
333 throw new IllegalArgumentException(msg);
334 }
335 }
336
337 /***
338 * Clear the array, reset the size to the initialCapacity and the number
339 * of elements to zero.
340 */
341 public synchronized void clear() {
342 numElements = 0;
343 internalArray = new double[initialCapacity];
344 }
345
346 /***
347 * Contracts the storage array to the (size of the element set) + 1 - to
348 * avoid a zero length array. This function also resets the startIndex to
349 * zero.
350 */
351 public synchronized void contract() {
352 double[] tempArray = new double[numElements + 1];
353
354
355 System.arraycopy(internalArray, startIndex, tempArray, 0, numElements);
356 internalArray = tempArray;
357
358
359 startIndex = 0;
360 }
361
362 /***
363 * Discards the <code>i<code> initial elements of the array. For example,
364 * if the array contains the elements 1,2,3,4, invoking
365 * <code>discardFrontElements(2)</code> will cause the first two elements
366 * to be discarded, leaving 3,4 in the array. Throws illegalArgumentException
367 * if i exceeds numElements.
368 *
369 * @param i the number of elements to discard from the front of the array
370 * @throws IllegalArgumentException if i is greater than numElements.
371 */
372 public synchronized void discardFrontElements(int i) {
373 if (i > numElements) {
374 String msg = "Cannot discard more elements than are" +
375 "contained in this array.";
376 throw new IllegalArgumentException(msg);
377 } else if (i < 0) {
378 String msg = "Cannot discard a negative number of elements.";
379 throw new IllegalArgumentException(msg);
380 } else {
381
382 numElements -= i;
383 startIndex += i;
384 }
385 if (shouldContract()) {
386 contract();
387 }
388 }
389
390 /***
391 * Expands the internal storage array using the expansion factor.
392 * <p>
393 * if <code>expansionMode</code> is set to MULTIPLICATIVE_MODE,
394 * the new array size will be <code>internalArray.length * expansionFactor.</code>
395 * If <code>expansionMode</code> is set to ADDITIVE_MODE, the length
396 * after expansion will be <code>internalArray.length + expansionFactor</code>
397 */
398 protected synchronized void expand() {
399
400
401
402
403
404
405 int newSize = 0;
406 if (expansionMode == MULTIPLICATIVE_MODE) {
407 newSize = (int) Math.ceil(internalArray.length * expansionFactor);
408 } else {
409 newSize = internalArray.length + Math.round(expansionFactor);
410 }
411 double[] tempArray = new double[newSize];
412
413
414 System.arraycopy(internalArray, 0, tempArray, 0, internalArray.length);
415 internalArray = tempArray;
416 }
417
418 /***
419 * Expands the internal storage array to the specified size.
420 *
421 * @param size Size of the new internal storage array
422 */
423 private synchronized void expandTo(int size) {
424 double[] tempArray = new double[size];
425
426 System.arraycopy(internalArray, 0, tempArray, 0, internalArray.length);
427 internalArray = tempArray;
428 }
429
430 /***
431 * The contraction criteria defines when the internal array will contract
432 * to store only the number of elements in the element array.
433 * If the <code>expansionMode</code> is <code>MULTIPLICATIVE_MODE</code>,
434 * contraction is triggered when the ratio between storage array length
435 * and <code>numElements</code> exceeds <code>contractionFactor</code>.
436 * If the <code>expansionMode</code> is <code>ADDITIVE_MODE</code>, the
437 * number of excess storage locations is compared to
438 * <code>contractionFactor.</code>
439 *
440 * @return the contraction criteria used to reclaim memory.
441 */
442 public float getContractionCriteria() {
443 return contractionCriteria;
444 }
445
446 /***
447 * Returns the element at the specified index
448 *
449 * @param index index to fetch a value from
450 * @return value stored at the specified index
451 * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
452 * zero or is greater than <code>getNumElements() - 1</code>.
453 */
454 public double getElement(int index) {
455 double value = Double.NaN;
456 if (index >= numElements) {
457 String msg =
458 "The index specified: " + index +
459 " is larger than the current number of elements";
460 throw new ArrayIndexOutOfBoundsException(msg);
461 } else if (index >= 0) {
462 value = internalArray[startIndex + index];
463 } else {
464 String msg =
465 "Elements cannot be retrieved from a negative array index";
466 throw new ArrayIndexOutOfBoundsException(msg);
467 }
468 return value;
469 }
470
471 /***
472 * Returns a double array containing the elements of this
473 * <code>ResizableArray</code>. This method returns a copy, not a
474 * reference to the underlying array, so that changes made to the returned
475 * array have no effect on this <code>ResizableArray.</code>
476 * @return the double array.
477 */
478 public double[] getElements() {
479 double[] elementArray = new double[numElements];
480 System.arraycopy( internalArray, startIndex, elementArray, 0,
481 numElements);
482 return elementArray;
483 }
484
485 /***
486 * The expansion factor controls the size of a new aray when an array
487 * needs to be expanded. The <code>expansionMode</code>
488 * determines whether the size of the array is multiplied by the
489 * <code>expansionFactor</code> (MULTIPLICATIVE_MODE) or if
490 * the expansion is additive (ADDITIVE_MODE -- <code>expansionFactor</code>
491 * storage locations added). The default <code>expansionMode</code> is
492 * MULTIPLICATIVE_MODE and the default <code>expansionFactor</code>
493 * is 2.0.
494 *
495 * @return the expansion factor of this expandable double array
496 */
497 public float getExpansionFactor() {
498 return expansionFactor;
499 }
500
501 /***
502 * The <code>expansionMode</code> determines whether the internal storage
503 * array grows additively (ADDITIVE_MODE) or multiplicatively
504 * (MULTIPLICATIVE_MODE) when it is expanded.
505 *
506 * @return Returns the expansionMode.
507 */
508 public int getExpansionMode() {
509 return expansionMode;
510 }
511
512 /***
513 * Notice the package scope on this method. This method is simply here
514 * for the JUnit test, it allows us check if the expansion is working
515 * properly after a number of expansions. This is not meant to be a part
516 * of the public interface of this class.
517 *
518 * @return the length of the internal storage array.
519 */
520 int getInternalLength() {
521 return (internalArray.length);
522 }
523
524 /***
525 * Returns the number of elements currently in the array. Please note
526 * that this is different from the length of the internal storage array.
527 *
528 * @return number of elements
529 */
530 public int getNumElements() {
531 return (numElements);
532 }
533
534 /***
535 * Returns the internal storage array. Note that this method returns
536 * a reference to the internal storage array, not a copy, and to correctly
537 * address elements of the array, the <code>startIndex</code> is
538 * required (available via the {@link #start} method). This method should
539 * only be used in cases where copying the internal array is not practical.
540 * The {@link #getElements} method should be used in all other cases.
541 *
542 *
543 * @return the internal storage array used by this object
544 */
545 public double[] getValues() {
546 return (internalArray);
547 }
548
549 /***
550 * Sets the contraction criteria for this ExpandContractDoubleArray.
551 *
552 * @param contractionCriteria contraction criteria
553 */
554 public void setContractionCriteria(float contractionCriteria) {
555 checkContractExpand(contractionCriteria, getExpansionFactor());
556 this.contractionCriteria = contractionCriteria;
557 }
558
559
560 /***
561 * Sets the element at the specified index. If the specified index is greater than
562 * <code>getNumElements() - 1</code>, the <code>numElements</code> property
563 * is increased to <code>index +1</code> and additional storage is allocated
564 * (if necessary) for the new element and all (uninitialized) elements
565 * between the new element and the previous end of the array).
566 *
567 * @param index index to store a value in
568 * @param value value to store at the specified index
569 * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
570 * zero.
571 */
572 public synchronized void setElement(int index, double value) {
573 if (index < 0) {
574 String msg = "Cannot set an element at a negative index";
575 throw new ArrayIndexOutOfBoundsException(msg);
576 }
577 if (index + 1 > numElements) {
578 numElements = index + 1;
579 }
580 if ((startIndex + index) >= internalArray.length) {
581 expandTo(startIndex + (index + 1));
582 }
583 internalArray[startIndex + index] = value;
584 }
585
586 /***
587 * Sets the expansionFactor. Throws IllegalArgumentException if the
588 * the following conditions are not met:
589 * <ul>
590 * <li><code>expansionFactor > 1</code></li>
591 * <li><code>contractionFactor >= expansionFactor</code></li>
592 * </ul>
593 * @param expansionFactor the new expansion factor value.
594 * @throws IllegalArgumentException if expansionFactor is <= 1 or greater
595 * than contractionFactor
596 */
597 public void setExpansionFactor(float expansionFactor) {
598 checkContractExpand(getContractionCriteria(), expansionFactor);
599
600 this.expansionFactor = expansionFactor;
601 }
602
603 /***
604 * Sets the <code>expansionMode</code>. The specified value must be one of
605 * ADDITIVE_MODE, MULTIPLICATIVE_MODE.
606 *
607 * @param expansionMode The expansionMode to set.
608 * @throws IllegalArgumentException if the specified mode value is not valid
609 */
610 public void setExpansionMode(int expansionMode) {
611 if (expansionMode != MULTIPLICATIVE_MODE &&
612 expansionMode != ADDITIVE_MODE) {
613 throw new IllegalArgumentException("Illegal expansionMode setting.");
614 }
615 this.expansionMode = expansionMode;
616 }
617
618 /***
619 * Sets the initial capacity. Should only be invoked by constructors.
620 *
621 * @param initialCapacity of the array
622 * @throws IllegalArgumentException if <code>initialCapacity</code> is not
623 * positive.
624 */
625 protected void setInitialCapacity(int initialCapacity) {
626 if (initialCapacity > 0) {
627 this.initialCapacity = initialCapacity;
628 } else {
629 String msg =
630 "The initial capacity supplied: " + initialCapacity +
631 "must be a positive integer";
632 throw new IllegalArgumentException(msg);
633 }
634 }
635
636 /***
637 * This function allows you to control the number of elements contained
638 * in this array, and can be used to "throw out" the last n values in an
639 * array. This function will also expand the internal array as needed.
640 *
641 * @param i a new number of elements
642 * @throws IllegalArgumentException if <code>i</code> is negative.
643 */
644 public synchronized void setNumElements(int i) {
645
646
647 if (i < 0) {
648 String msg =
649 "Number of elements must be zero or a positive " + "integer";
650 throw new IllegalArgumentException(msg);
651 }
652
653
654
655 if ((startIndex + i) > internalArray.length) {
656 expandTo(startIndex + i);
657 }
658
659
660 numElements = i;
661 }
662
663 /***
664 * Returns true if the internal storage array has too many unused
665 * storage positions.
666 *
667 * @return true if array satisfies the contraction criteria
668 */
669 private synchronized boolean shouldContract() {
670 if (expansionMode == MULTIPLICATIVE_MODE) {
671 return (internalArray.length / numElements) > contractionCriteria;
672 } else {
673 return (internalArray.length - numElements) > contractionCriteria;
674 }
675 }
676
677 /***
678 * Returns the starting index of the internal array. The starting index is
679 * the position of the first addressable element in the internal storage
680 * array. The addressable elements in the array are <code>
681 * internalArray[startIndex],...,internalArray[startIndex + numElements -1]
682 * </code>
683 *
684 * @return starting index
685 */
686 public int start() {
687 return startIndex;
688 }
689
690 }