1 /*
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.nio;
27
28 import java.util.Spliterator;
29 import jdk.internal.HotSpotIntrinsicCandidate;
30
31 /**
32 * A container for data of a specific primitive type.
33 *
34 * <p> A buffer is a linear, finite sequence of elements of a specific
35 * primitive type. Aside from its content, the essential properties of a
36 * buffer are its capacity, limit, and position: </p>
37 *
38 * <blockquote>
39 *
40 * <p> A buffer's <i>capacity</i> is the number of elements it contains. The
41 * capacity of a buffer is never negative and never changes. </p>
42 *
43 * <p> A buffer's <i>limit</i> is the index of the first element that should
44 * not be read or written. A buffer's limit is never negative and is never
45 * greater than its capacity. </p>
46 *
47 * <p> A buffer's <i>position</i> is the index of the next element to be
48 * read or written. A buffer's position is never negative and is never
49 * greater than its limit. </p>
50 *
51 * </blockquote>
52 *
53 * <p> There is one subclass of this class for each non-boolean primitive type.
54 *
55 *
56 * <h2> Transferring data </h2>
57 *
58 * <p> Each subclass of this class defines two categories of <i>get</i> and
59 * <i>put</i> operations: </p>
60 *
61 * <blockquote>
62 *
63 * <p> <i>Relative</i> operations read or write one or more elements starting
64 * at the current position and then increment the position by the number of
65 * elements transferred. If the requested transfer exceeds the limit then a
66 * relative <i>get</i> operation throws a {@link BufferUnderflowException}
67 * and a relative <i>put</i> operation throws a {@link
68 * BufferOverflowException}; in either case, no data is transferred. </p>
69 *
70 * <p> <i>Absolute</i> operations take an explicit element index and do not
71 * affect the position. Absolute <i>get</i> and <i>put</i> operations throw
72 * an {@link IndexOutOfBoundsException} if the index argument exceeds the
73 * limit. </p>
74 *
75 * </blockquote>
76 *
77 * <p> Data may also, of course, be transferred in to or out of a buffer by the
78 * I/O operations of an appropriate channel, which are always relative to the
79 * current position.
80 *
81 *
82 * <h2> Marking and resetting </h2>
83 *
84 * <p> A buffer's <i>mark</i> is the index to which its position will be reset
85 * when the {@link #reset reset} method is invoked. The mark is not always
86 * defined, but when it is defined it is never negative and is never greater
87 * than the position. If the mark is defined then it is discarded when the
88 * position or the limit is adjusted to a value smaller than the mark. If the
89 * mark is not defined then invoking the {@link #reset reset} method causes an
90 * {@link InvalidMarkException} to be thrown.
91 *
92 *
93 * <h2> Invariants </h2>
94 *
95 * <p> The following invariant holds for the mark, position, limit, and
96 * capacity values:
97 *
98 * <blockquote>
99 * <tt>0</tt> <tt><=</tt>
100 * <i>mark</i> <tt><=</tt>
101 * <i>position</i> <tt><=</tt>
102 * <i>limit</i> <tt><=</tt>
103 * <i>capacity</i>
104 * </blockquote>
105 *
106 * <p> A newly-created buffer always has a position of zero and a mark that is
107 * undefined. The initial limit may be zero, or it may be some other value
108 * that depends upon the type of the buffer and the manner in which it is
109 * constructed. Each element of a newly-allocated buffer is initialized
110 * to zero.
111 *
112 *
113 * <h2> Clearing, flipping, and rewinding </h2>
114 *
115 * <p> In addition to methods for accessing the position, limit, and capacity
116 * values and for marking and resetting, this class also defines the following
117 * operations upon buffers:
118 *
119 * <ul>
120 *
121 * <li><p> {@link #clear} makes a buffer ready for a new sequence of
122 * channel-read or relative <i>put</i> operations: It sets the limit to the
123 * capacity and the position to zero. </p></li>
124 *
125 * <li><p> {@link #flip} makes a buffer ready for a new sequence of
126 * channel-write or relative <i>get</i> operations: It sets the limit to the
127 * current position and then sets the position to zero. </p></li>
128 *
129 * <li><p> {@link #rewind} makes a buffer ready for re-reading the data that
130 * it already contains: It leaves the limit unchanged and sets the position
131 * to zero. </p></li>
132 *
133 * </ul>
134 *
135 *
136 * <h2> Read-only buffers </h2>
137 *
138 * <p> Every buffer is readable, but not every buffer is writable. The
139 * mutation methods of each buffer class are specified as <i>optional
140 * operations</i> that will throw a {@link ReadOnlyBufferException} when
141 * invoked upon a read-only buffer. A read-only buffer does not allow its
142 * content to be changed, but its mark, position, and limit values are mutable.
143 * Whether or not a buffer is read-only may be determined by invoking its
144 * {@link #isReadOnly isReadOnly} method.
145 *
146 *
147 * <h2> Thread safety </h2>
148 *
149 * <p> Buffers are not safe for use by multiple concurrent threads. If a
150 * buffer is to be used by more than one thread then access to the buffer
151 * should be controlled by appropriate synchronization.
152 *
153 *
154 * <h2> Invocation chaining </h2>
155 *
156 * <p> Methods in this class that do not otherwise have a value to return are
157 * specified to return the buffer upon which they are invoked. This allows
158 * method invocations to be chained; for example, the sequence of statements
159 *
160 * <blockquote><pre>
161 * b.flip();
162 * b.position(23);
163 * b.limit(42);</pre></blockquote>
164 *
165 * can be replaced by the single, more compact statement
166 *
167 * <blockquote><pre>
168 * b.flip().position(23).limit(42);</pre></blockquote>
169 *
170 *
171 * @author Mark Reinhold
172 * @author JSR-51 Expert Group
173 * @since 1.4
174 */
175
176 public abstract class Buffer {
177
178 /**
179 * The characteristics of Spliterators that traverse and split elements
180 * maintained in Buffers.
181 */
182 static final int SPLITERATOR_CHARACTERISTICS =
183 Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.ORDERED;
184
185 // Invariants: mark <= position <= limit <= capacity
186 private int mark = -1;
187 private int position = 0;
188 private int limit;
189 private int capacity;
190
191 // Used only by direct buffers
192 // NOTE: hoisted here for speed in JNI GetDirectBufferAddress
193 long address;
194
195 // Creates a new buffer with the given mark, position, limit, and capacity,
196 // after checking invariants.
197 //
198 Buffer(int mark, int pos, int lim, int cap) { // package-private
199 if (cap < 0)
200 throw new IllegalArgumentException("Negative capacity: " + cap);
201 this.capacity = cap;
202 limit(lim);
203 position(pos);
204 if (mark >= 0) {
205 if (mark > pos)
206 throw new IllegalArgumentException("mark > position: ("
207 + mark + " > " + pos + ")");
208 this.mark = mark;
209 }
210 }
211
212 /**
213 * Returns this buffer's capacity.
214 *
215 * @return The capacity of this buffer
216 */
217 public final int capacity() {
218 return capacity;
219 }
220
221 /**
222 * Returns this buffer's position.
223 *
224 * @return The position of this buffer
225 */
226 public final int position() {
227 return position;
228 }
229
230 /**
231 * Sets this buffer's position. If the mark is defined and larger than the
232 * new position then it is discarded.
233 *
234 * @param newPosition
235 * The new position value; must be non-negative
236 * and no larger than the current limit
237 *
238 * @return This buffer
239 *
240 * @throws IllegalArgumentException
241 * If the preconditions on <tt>newPosition</tt> do not hold
242 */
243 public Buffer position(int newPosition) {
244 if ((newPosition > limit) || (newPosition < 0))
245 throw new IllegalArgumentException();
246 position = newPosition;
247 if (mark > position) mark = -1;
248 return this;
249 }
250
251 /**
252 * Returns this buffer's limit.
253 *
254 * @return The limit of this buffer
255 */
256 public final int limit() {
257 return limit;
258 }
259
260 /**
261 * Sets this buffer's limit. If the position is larger than the new limit
262 * then it is set to the new limit. If the mark is defined and larger than
263 * the new limit then it is discarded.
264 *
265 * @param newLimit
266 * The new limit value; must be non-negative
267 * and no larger than this buffer's capacity
268 *
269 * @return This buffer
270 *
271 * @throws IllegalArgumentException
272 * If the preconditions on <tt>newLimit</tt> do not hold
273 */
274 public Buffer limit(int newLimit) {
275 if ((newLimit > capacity) || (newLimit < 0))
276 throw new IllegalArgumentException();
277 limit = newLimit;
278 if (position > limit) position = limit;
279 if (mark > limit) mark = -1;
280 return this;
281 }
282
283 /**
284 * Sets this buffer's mark at its position.
285 *
286 * @return This buffer
287 */
288 public Buffer mark() {
289 mark = position;
290 return this;
291 }
292
293 /**
294 * Resets this buffer's position to the previously-marked position.
295 *
296 * <p> Invoking this method neither changes nor discards the mark's
297 * value. </p>
298 *
299 * @return This buffer
300 *
301 * @throws InvalidMarkException
302 * If the mark has not been set
303 */
304 public Buffer reset() {
305 int m = mark;
306 if (m < 0)
307 throw new InvalidMarkException();
308 position = m;
309 return this;
310 }
311
312 /**
313 * Clears this buffer. The position is set to zero, the limit is set to
314 * the capacity, and the mark is discarded.
315 *
316 * <p> Invoke this method before using a sequence of channel-read or
317 * <i>put</i> operations to fill this buffer. For example:
318 *
319 * <blockquote><pre>
320 * buf.clear(); // Prepare buffer for reading
321 * in.read(buf); // Read data</pre></blockquote>
322 *
323 * <p> This method does not actually erase the data in the buffer, but it
324 * is named as if it did because it will most often be used in situations
325 * in which that might as well be the case. </p>
326 *
327 * @return This buffer
328 */
329 public Buffer clear() {
330 position = 0;
331 limit = capacity;
332 mark = -1;
333 return this;
334 }
335
336 /**
337 * Flips this buffer. The limit is set to the current position and then
338 * the position is set to zero. If the mark is defined then it is
339 * discarded.
340 *
341 * <p> After a sequence of channel-read or <i>put</i> operations, invoke
342 * this method to prepare for a sequence of channel-write or relative
343 * <i>get</i> operations. For example:
344 *
345 * <blockquote><pre>
346 * buf.put(magic); // Prepend header
347 * in.read(buf); // Read data into rest of buffer
348 * buf.flip(); // Flip buffer
349 * out.write(buf); // Write header + data to channel</pre></blockquote>
350 *
351 * <p> This method is often used in conjunction with the {@link
352 * java.nio.ByteBuffer#compact compact} method when transferring data from
353 * one place to another. </p>
354 *
355 * @return This buffer
356 */
357 public Buffer flip() {
358 limit = position;
359 position = 0;
360 mark = -1;
361 return this;
362 }
363
364 /**
365 * Rewinds this buffer. The position is set to zero and the mark is
366 * discarded.
367 *
368 * <p> Invoke this method before a sequence of channel-write or <i>get</i>
369 * operations, assuming that the limit has already been set
370 * appropriately. For example:
371 *
372 * <blockquote><pre>
373 * out.write(buf); // Write remaining data
374 * buf.rewind(); // Rewind buffer
375 * buf.get(array); // Copy data into array</pre></blockquote>
376 *
377 * @return This buffer
378 */
379 public Buffer rewind() {
380 position = 0;
381 mark = -1;
382 return this;
383 }
384
385 /**
386 * Returns the number of elements between the current position and the
387 * limit.
388 *
389 * @return The number of elements remaining in this buffer
390 */
391 public final int remaining() {
392 return limit - position;
393 }
394
395 /**
396 * Tells whether there are any elements between the current position and
397 * the limit.
398 *
399 * @return <tt>true</tt> if, and only if, there is at least one element
400 * remaining in this buffer
401 */
402 public final boolean hasRemaining() {
403 return position < limit;
404 }
405
406 /**
407 * Tells whether or not this buffer is read-only.
408 *
409 * @return <tt>true</tt> if, and only if, this buffer is read-only
410 */
411 public abstract boolean isReadOnly();
412
413 /**
414 * Tells whether or not this buffer is backed by an accessible
415 * array.
416 *
417 * <p> If this method returns <tt>true</tt> then the {@link #array() array}
418 * and {@link #arrayOffset() arrayOffset} methods may safely be invoked.
419 * </p>
420 *
421 * @return <tt>true</tt> if, and only if, this buffer
422 * is backed by an array and is not read-only
423 *
424 * @since 1.6
425 */
426 public abstract boolean hasArray();
427
428 /**
429 * Returns the array that backs this
430 * buffer <i>(optional operation)</i>.
431 *
432 * <p> This method is intended to allow array-backed buffers to be
433 * passed to native code more efficiently. Concrete subclasses
434 * provide more strongly-typed return values for this method.
435 *
436 * <p> Modifications to this buffer's content will cause the returned
437 * array's content to be modified, and vice versa.
438 *
439 * <p> Invoke the {@link #hasArray hasArray} method before invoking this
440 * method in order to ensure that this buffer has an accessible backing
441 * array. </p>
442 *
443 * @return The array that backs this buffer
444 *
445 * @throws ReadOnlyBufferException
446 * If this buffer is backed by an array but is read-only
447 *
448 * @throws UnsupportedOperationException
449 * If this buffer is not backed by an accessible array
450 *
451 * @since 1.6
452 */
453 public abstract Object array();
454
455 /**
456 * Returns the offset within this buffer's backing array of the first
457 * element of the buffer <i>(optional operation)</i>.
458 *
459 * <p> If this buffer is backed by an array then buffer position <i>p</i>
460 * corresponds to array index <i>p</i> + <tt>arrayOffset()</tt>.
461 *
462 * <p> Invoke the {@link #hasArray hasArray} method before invoking this
463 * method in order to ensure that this buffer has an accessible backing
464 * array. </p>
465 *
466 * @return The offset within this buffer's array
467 * of the first element of the buffer
468 *
469 * @throws ReadOnlyBufferException
470 * If this buffer is backed by an array but is read-only
471 *
472 * @throws UnsupportedOperationException
473 * If this buffer is not backed by an accessible array
474 *
475 * @since 1.6
476 */
477 public abstract int arrayOffset();
478
479 /**
480 * Tells whether or not this buffer is
481 * <a href="ByteBuffer.html#direct"><i>direct</i></a>.
482 *
483 * @return <tt>true</tt> if, and only if, this buffer is direct
484 *
485 * @since 1.6
486 */
487 public abstract boolean isDirect();
488
489
490 // -- Package-private methods for bounds checking, etc. --
491
492 /**
493 * Checks the current position against the limit, throwing a {@link
494 * BufferUnderflowException} if it is not smaller than the limit, and then
495 * increments the position.
496 *
497 * @return The current position value, before it is incremented
498 */
499 final int nextGetIndex() { // package-private
500 if (position >= limit)
501 throw new BufferUnderflowException();
502 return position++;
503 }
504
505 final int nextGetIndex(int nb) { // package-private
506 if (limit - position < nb)
507 throw new BufferUnderflowException();
508 int p = position;
509 position += nb;
510 return p;
511 }
512
513 /**
514 * Checks the current position against the limit, throwing a {@link
515 * BufferOverflowException} if it is not smaller than the limit, and then
516 * increments the position.
517 *
518 * @return The current position value, before it is incremented
519 */
520 final int nextPutIndex() { // package-private
521 if (position >= limit)
522 throw new BufferOverflowException();
523 return position++;
524 }
525
526 final int nextPutIndex(int nb) { // package-private
527 if (limit - position < nb)
528 throw new BufferOverflowException();
529 int p = position;
530 position += nb;
531 return p;
532 }
533
534 /**
535 * Checks the given index against the limit, throwing an {@link
536 * IndexOutOfBoundsException} if it is not smaller than the limit
537 * or is smaller than zero.
538 */
539 @HotSpotIntrinsicCandidate
540 final int checkIndex(int i) { // package-private
541 if ((i < 0) || (i >= limit))
542 throw new IndexOutOfBoundsException();
543 return i;
544 }
545
546 final int checkIndex(int i, int nb) { // package-private
547 if ((i < 0) || (nb > limit - i))
548 throw new IndexOutOfBoundsException();
549 return i;
550 }
551
552 final int markValue() { // package-private
553 return mark;
554 }
555
556 final void truncate() { // package-private
557 mark = -1;
558 position = 0;
559 limit = 0;
560 capacity = 0;
561 }
562
563 final void discardMark() { // package-private
564 mark = -1;
565 }
566
567 static void checkBounds(int off, int len, int size) { // package-private
568 if ((off | len | (off + len) | (size - (off + len))) < 0)
569 throw new IndexOutOfBoundsException();
570 }
571
572 }