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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: 348519 $ $Date: 2005-11-23 12:12:18 -0700 (Wed, 23 Nov 2005) $
70 */
71 public class ResizableDoubleArray implements DoubleArray, Serializable {
72
73 /** Serializable version identifier */
74 private 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 synchronized double getElement(int index) {
455 if (index >= numElements) {
456 String msg =
457 "The index specified: " + index +
458 " is larger than the current number of elements";
459 throw new ArrayIndexOutOfBoundsException(msg);
460 } else if (index >= 0) {
461 return internalArray[startIndex + index];
462 } else {
463 String msg =
464 "Elements cannot be retrieved from a negative array index";
465 throw new ArrayIndexOutOfBoundsException(msg);
466 }
467 }
468
469 /**
470 * Returns a double array containing the elements of this
471 * <code>ResizableArray</code>. This method returns a copy, not a
472 * reference to the underlying array, so that changes made to the returned
473 * array have no effect on this <code>ResizableArray.</code>
474 * @return the double array.
475 */
476 public synchronized double[] getElements() {
477 double[] elementArray = new double[numElements];
478 System.arraycopy( internalArray, startIndex, elementArray, 0,
479 numElements);
480 return elementArray;
481 }
482
483 /**
484 * The expansion factor controls the size of a new aray when an array
485 * needs to be expanded. The <code>expansionMode</code>
486 * determines whether the size of the array is multiplied by the
487 * <code>expansionFactor</code> (MULTIPLICATIVE_MODE) or if
488 * the expansion is additive (ADDITIVE_MODE -- <code>expansionFactor</code>
489 * storage locations added). The default <code>expansionMode</code> is
490 * MULTIPLICATIVE_MODE and the default <code>expansionFactor</code>
491 * is 2.0.
492 *
493 * @return the expansion factor of this expandable double array
494 */
495 public float getExpansionFactor() {
496 return expansionFactor;
497 }
498
499 /**
500 * The <code>expansionMode</code> determines whether the internal storage
501 * array grows additively (ADDITIVE_MODE) or multiplicatively
502 * (MULTIPLICATIVE_MODE) when it is expanded.
503 *
504 * @return Returns the expansionMode.
505 */
506 public int getExpansionMode() {
507 return expansionMode;
508 }
509
510 /**
511 * Notice the package scope on this method. This method is simply here
512 * for the JUnit test, it allows us check if the expansion is working
513 * properly after a number of expansions. This is not meant to be a part
514 * of the public interface of this class.
515 *
516 * @return the length of the internal storage array.
517 */
518 synchronized int getInternalLength() {
519 return (internalArray.length);
520 }
521
522 /**
523 * Returns the number of elements currently in the array. Please note
524 * that this is different from the length of the internal storage array.
525 *
526 * @return number of elements
527 */
528 public synchronized int getNumElements() {
529 return (numElements);
530 }
531
532 /**
533 * Returns the internal storage array. Note that this method returns
534 * a reference to the internal storage array, not a copy, and to correctly
535 * address elements of the array, the <code>startIndex</code> is
536 * required (available via the {@link #start} method). This method should
537 * only be used in cases where copying the internal array is not practical.
538 * The {@link #getElements} method should be used in all other cases.
539 *
540 *
541 * @return the internal storage array used by this object
542 */
543 public synchronized double[] getValues() {
544 return (internalArray);
545 }
546
547 /**
548 * Sets the contraction criteria for this ExpandContractDoubleArray.
549 *
550 * @param contractionCriteria contraction criteria
551 */
552 public void setContractionCriteria(float contractionCriteria) {
553 checkContractExpand(contractionCriteria, getExpansionFactor());
554 this.contractionCriteria = contractionCriteria;
555 }
556
557
558 /**
559 * Sets the element at the specified index. If the specified index is greater than
560 * <code>getNumElements() - 1</code>, the <code>numElements</code> property
561 * is increased to <code>index +1</code> and additional storage is allocated
562 * (if necessary) for the new element and all (uninitialized) elements
563 * between the new element and the previous end of the array).
564 *
565 * @param index index to store a value in
566 * @param value value to store at the specified index
567 * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
568 * zero.
569 */
570 public synchronized void setElement(int index, double value) {
571 if (index < 0) {
572 String msg = "Cannot set an element at a negative index";
573 throw new ArrayIndexOutOfBoundsException(msg);
574 }
575 if (index + 1 > numElements) {
576 numElements = index + 1;
577 }
578 if ((startIndex + index) >= internalArray.length) {
579 expandTo(startIndex + (index + 1));
580 }
581 internalArray[startIndex + index] = value;
582 }
583
584 /**
585 * Sets the expansionFactor. Throws IllegalArgumentException if the
586 * the following conditions are not met:
587 * <ul>
588 * <li><code>expansionFactor > 1</code></li>
589 * <li><code>contractionFactor >= expansionFactor</code></li>
590 * </ul>
591 * @param expansionFactor the new expansion factor value.
592 * @throws IllegalArgumentException if expansionFactor is <= 1 or greater
593 * than contractionFactor
594 */
595 public void setExpansionFactor(float expansionFactor) {
596 checkContractExpand(getContractionCriteria(), expansionFactor);
597
598 this.expansionFactor = expansionFactor;
599 }
600
601 /**
602 * Sets the <code>expansionMode</code>. The specified value must be one of
603 * ADDITIVE_MODE, MULTIPLICATIVE_MODE.
604 *
605 * @param expansionMode The expansionMode to set.
606 * @throws IllegalArgumentException if the specified mode value is not valid
607 */
608 public void setExpansionMode(int expansionMode) {
609 if (expansionMode != MULTIPLICATIVE_MODE &&
610 expansionMode != ADDITIVE_MODE) {
611 throw new IllegalArgumentException("Illegal expansionMode setting.");
612 }
613 this.expansionMode = expansionMode;
614 }
615
616 /**
617 * Sets the initial capacity. Should only be invoked by constructors.
618 *
619 * @param initialCapacity of the array
620 * @throws IllegalArgumentException if <code>initialCapacity</code> is not
621 * positive.
622 */
623 protected void setInitialCapacity(int initialCapacity) {
624 if (initialCapacity > 0) {
625 this.initialCapacity = initialCapacity;
626 } else {
627 String msg =
628 "The initial capacity supplied: " + initialCapacity +
629 "must be a positive integer";
630 throw new IllegalArgumentException(msg);
631 }
632 }
633
634 /**
635 * This function allows you to control the number of elements contained
636 * in this array, and can be used to "throw out" the last n values in an
637 * array. This function will also expand the internal array as needed.
638 *
639 * @param i a new number of elements
640 * @throws IllegalArgumentException if <code>i</code> is negative.
641 */
642 public synchronized void setNumElements(int i) {
643
644
645 if (i < 0) {
646 String msg =
647 "Number of elements must be zero or a positive " + "integer";
648 throw new IllegalArgumentException(msg);
649 }
650
651
652
653 if ((startIndex + i) > internalArray.length) {
654 expandTo(startIndex + i);
655 }
656
657
658 numElements = i;
659 }
660
661 /**
662 * Returns true if the internal storage array has too many unused
663 * storage positions.
664 *
665 * @return true if array satisfies the contraction criteria
666 */
667 private synchronized boolean shouldContract() {
668 if (expansionMode == MULTIPLICATIVE_MODE) {
669 return (internalArray.length / numElements) > contractionCriteria;
670 } else {
671 return (internalArray.length - numElements) > contractionCriteria;
672 }
673 }
674
675 /**
676 * Returns the starting index of the internal array. The starting index is
677 * the position of the first addressable element in the internal storage
678 * array. The addressable elements in the array are <code>
679 * internalArray[startIndex],...,internalArray[startIndex + numElements -1]
680 * </code>
681 *
682 * @return starting index
683 */
684 public synchronized int start() {
685 return startIndex;
686 }
687
688 }