1 /*
2 * Copyright (c) 1994, 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
18 * 2 along with this work; if not, write to the Free Software Foundation,
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
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27
28 import java.util.Arrays;
29
30 /**
31 * A thread-safe, mutable sequence of characters.
32 * A string buffer is like a {@link String}, but can be modified. At any
33 * point in time it contains some particular sequence of characters, but
34 * the length and content of the sequence can be changed through certain
35 * method calls.
36 * <p>
37 * String buffers are safe for use by multiple threads. The methods
38 * are synchronized where necessary so that all the operations on any
39 * particular instance behave as if they occur in some serial order
40 * that is consistent with the order of the method calls made by each of
41 * the individual threads involved.
42 * <p>
43 * The principal operations on a {@code StringBuffer} are the
44 * {@code append} and {@code insert} methods, which are
45 * overloaded so as to accept data of any type. Each effectively
46 * converts a given datum to a string and then appends or inserts the
47 * characters of that string to the string buffer. The
48 * {@code append} method always adds these characters at the end
49 * of the buffer; the {@code insert} method adds the characters at
50 * a specified point.
51 * <p>
52 * For example, if {@code z} refers to a string buffer object
53 * whose current contents are {@code "start"}, then
54 * the method call {@code z.append("le")} would cause the string
55 * buffer to contain {@code "startle"}, whereas
56 * {@code z.insert(4, "le")} would alter the string buffer to
57 * contain {@code "starlet"}.
58 * <p>
59 * In general, if sb refers to an instance of a {@code StringBuffer},
60 * then {@code sb.append(x)} has the same effect as
61 * {@code sb.insert(sb.length(), x)}.
62 * <p>
63 * Whenever an operation occurs involving a source sequence (such as
64 * appending or inserting from a source sequence), this class synchronizes
65 * only on the string buffer performing the operation, not on the source.
66 * Note that while {@code StringBuffer} is designed to be safe to use
67 * concurrently from multiple threads, if the constructor or the
68 * {@code append} or {@code insert} operation is passed a source sequence
69 * that is shared across threads, the calling code must ensure
70 * that the operation has a consistent and unchanging view of the source
71 * sequence for the duration of the operation.
72 * This could be satisfied by the caller holding a lock during the
73 * operation's call, by using an immutable source sequence, or by not
74 * sharing the source sequence across threads.
75 * <p>
76 * Every string buffer has a capacity. As long as the length of the
77 * character sequence contained in the string buffer does not exceed
78 * the capacity, it is not necessary to allocate a new internal
79 * buffer array. If the internal buffer overflows, it is
80 * automatically made larger.
81 * <p>
82 * Unless otherwise noted, passing a {@code null} argument to a constructor
83 * or method in this class will cause a {@link NullPointerException} to be
84 * thrown.
85 * <p>
86 * As of release JDK 5, this class has been supplemented with an equivalent
87 * class designed for use by a single thread, {@link StringBuilder}. The
88 * {@code StringBuilder} class should generally be used in preference to
89 * this one, as it supports all of the same operations but it is faster, as
90 * it performs no synchronization.
91 *
92 * @author Arthur van Hoff
93 * @see java.lang.StringBuilder
94 * @see java.lang.String
95 * @since 1.0
96 */
97 public final class StringBuffer
98 extends AbstractStringBuilder
99 implements java.io.Serializable, CharSequence
100 {
101
102 /**
103 * A cache of the last value returned by toString. Cleared
104 * whenever the StringBuffer is modified.
105 */
106 private transient char[] toStringCache;
107
108 /** use serialVersionUID from JDK 1.0.2 for interoperability */
109 static final long serialVersionUID = 3388685877147921107L;
110
111 /**
112 * Constructs a string buffer with no characters in it and an
113 * initial capacity of 16 characters.
114 */
115 public StringBuffer() {
116 super(16);
117 }
118
119 /**
120 * Constructs a string buffer with no characters in it and
121 * the specified initial capacity.
122 *
123 * @param capacity the initial capacity.
124 * @exception NegativeArraySizeException if the {@code capacity}
125 * argument is less than {@code 0}.
126 */
127 public StringBuffer(int capacity) {
128 super(capacity);
129 }
130
131 /**
132 * Constructs a string buffer initialized to the contents of the
133 * specified string. The initial capacity of the string buffer is
134 * {@code 16} plus the length of the string argument.
135 *
136 * @param str the initial contents of the buffer.
137 */
138 public StringBuffer(String str) {
139 super(str.length() + 16);
140 append(str);
141 }
142
143 /**
144 * Constructs a string buffer that contains the same characters
145 * as the specified {@code CharSequence}. The initial capacity of
146 * the string buffer is {@code 16} plus the length of the
147 * {@code CharSequence} argument.
148 * <p>
149 * If the length of the specified {@code CharSequence} is
150 * less than or equal to zero, then an empty buffer of capacity
151 * {@code 16} is returned.
152 *
153 * @param seq the sequence to copy.
154 * @since 1.5
155 */
156 public StringBuffer(CharSequence seq) {
157 this(seq.length() + 16);
158 append(seq);
159 }
160
161 @Override
162 public synchronized int length() {
163 return count;
164 }
165
166 @Override
167 public synchronized int capacity() {
168 return value.length;
169 }
170
171
172 @Override
173 public synchronized void ensureCapacity(int minimumCapacity) {
174 if (minimumCapacity > value.length) {
175 expandCapacity(minimumCapacity);
176 }
177 }
178
179 /**
180 * @since 1.5
181 */
182 @Override
183 public synchronized void trimToSize() {
184 super.trimToSize();
185 }
186
187 /**
188 * @throws IndexOutOfBoundsException {@inheritDoc}
189 * @see #length()
190 */
191 @Override
192 public synchronized void setLength(int newLength) {
193 toStringCache = null;
194 super.setLength(newLength);
195 }
196
197 /**
198 * @throws IndexOutOfBoundsException {@inheritDoc}
199 * @see #length()
200 */
201 @Override
202 public synchronized char charAt(int index) {
203 if ((index < 0) || (index >= count))
204 throw new StringIndexOutOfBoundsException(index);
205 return value[index];
206 }
207
208 /**
209 * @throws IndexOutOfBoundsException {@inheritDoc}
210 * @since 1.5
211 */
212 @Override
213 public synchronized int codePointAt(int index) {
214 return super.codePointAt(index);
215 }
216
217 /**
218 * @throws IndexOutOfBoundsException {@inheritDoc}
219 * @since 1.5
220 */
221 @Override
222 public synchronized int codePointBefore(int index) {
223 return super.codePointBefore(index);
224 }
225
226 /**
227 * @throws IndexOutOfBoundsException {@inheritDoc}
228 * @since 1.5
229 */
230 @Override
231 public synchronized int codePointCount(int beginIndex, int endIndex) {
232 return super.codePointCount(beginIndex, endIndex);
233 }
234
235 /**
236 * @throws IndexOutOfBoundsException {@inheritDoc}
237 * @since 1.5
238 */
239 @Override
240 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
241 return super.offsetByCodePoints(index, codePointOffset);
242 }
243
244 /**
245 * @throws IndexOutOfBoundsException {@inheritDoc}
246 */
247 @Override
248 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
249 int dstBegin)
250 {
251 super.getChars(srcBegin, srcEnd, dst, dstBegin);
252 }
253
254 /**
255 * @throws IndexOutOfBoundsException {@inheritDoc}
256 * @see #length()
257 */
258 @Override
259 public synchronized void setCharAt(int index, char ch) {
260 if ((index < 0) || (index >= count))
261 throw new StringIndexOutOfBoundsException(index);
262 toStringCache = null;
263 value[index] = ch;
264 }
265
266 @Override
267 public synchronized StringBuffer append(Object obj) {
268 toStringCache = null;
269 super.append(String.valueOf(obj));
270 return this;
271 }
272
273 @Override
274 public synchronized StringBuffer append(String str) {
275 toStringCache = null;
276 super.append(str);
277 return this;
278 }
279
280 /**
281 * Appends the specified {@code StringBuffer} to this sequence.
282 * <p>
283 * The characters of the {@code StringBuffer} argument are appended,
284 * in order, to the contents of this {@code StringBuffer}, increasing the
285 * length of this {@code StringBuffer} by the length of the argument.
286 * If {@code sb} is {@code null}, then the four characters
287 * {@code "null"} are appended to this {@code StringBuffer}.
288 * <p>
289 * Let <i>n</i> be the length of the old character sequence, the one
290 * contained in the {@code StringBuffer} just prior to execution of the
291 * {@code append} method. Then the character at index <i>k</i> in
292 * the new character sequence is equal to the character at index <i>k</i>
293 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
294 * otherwise, it is equal to the character at index <i>k-n</i> in the
295 * argument {@code sb}.
296 * <p>
297 * This method synchronizes on {@code this}, the destination
298 * object, but does not synchronize on the source ({@code sb}).
299 *
300 * @param sb the {@code StringBuffer} to append.
301 * @return a reference to this object.
302 * @since 1.4
303 */
304 public synchronized StringBuffer append(StringBuffer sb) {
305 toStringCache = null;
306 super.append(sb);
307 return this;
308 }
309
310 /**
311 * @since 1.8
312 */
313 @Override
314 synchronized StringBuffer append(AbstractStringBuilder asb) {
315 toStringCache = null;
316 super.append(asb);
317 return this;
318 }
319
320 /**
321 * Appends the specified {@code CharSequence} to this
322 * sequence.
323 * <p>
324 * The characters of the {@code CharSequence} argument are appended,
325 * in order, increasing the length of this sequence by the length of the
326 * argument.
327 *
328 * <p>The result of this method is exactly the same as if it were an
329 * invocation of this.append(s, 0, s.length());
330 *
331 * <p>This method synchronizes on {@code this}, the destination
332 * object, but does not synchronize on the source ({@code s}).
333 *
334 * <p>If {@code s} is {@code null}, then the four characters
335 * {@code "null"} are appended.
336 *
337 * @param s the {@code CharSequence} to append.
338 * @return a reference to this object.
339 * @since 1.5
340 */
341 @Override
342 public synchronized StringBuffer append(CharSequence s) {
343 toStringCache = null;
344 super.append(s);
345 return this;
346 }
347
348 /**
349 * @throws IndexOutOfBoundsException {@inheritDoc}
350 * @since 1.5
351 */
352 @Override
353 public synchronized StringBuffer append(CharSequence s, int start, int end)
354 {
355 toStringCache = null;
356 super.append(s, start, end);
357 return this;
358 }
359
360 @Override
361 public synchronized StringBuffer append(char[] str) {
362 toStringCache = null;
363 super.append(str);
364 return this;
365 }
366
367 /**
368 * @throws IndexOutOfBoundsException {@inheritDoc}
369 */
370 @Override
371 public synchronized StringBuffer append(char[] str, int offset, int len) {
372 toStringCache = null;
373 super.append(str, offset, len);
374 return this;
375 }
376
377 @Override
378 public synchronized StringBuffer append(boolean b) {
379 toStringCache = null;
380 super.append(b);
381 return this;
382 }
383
384 @Override
385 public synchronized StringBuffer append(char c) {
386 toStringCache = null;
387 super.append(c);
388 return this;
389 }
390
391 @Override
392 public synchronized StringBuffer append(int i) {
393 toStringCache = null;
394 super.append(i);
395 return this;
396 }
397
398 /**
399 * @since 1.5
400 */
401 @Override
402 public synchronized StringBuffer appendCodePoint(int codePoint) {
403 toStringCache = null;
404 super.appendCodePoint(codePoint);
405 return this;
406 }
407
408 @Override
409 public synchronized StringBuffer append(long lng) {
410 toStringCache = null;
411 super.append(lng);
412 return this;
413 }
414
415 @Override
416 public synchronized StringBuffer append(float f) {
417 toStringCache = null;
418 super.append(f);
419 return this;
420 }
421
422 @Override
423 public synchronized StringBuffer append(double d) {
424 toStringCache = null;
425 super.append(d);
426 return this;
427 }
428
429 /**
430 * @throws StringIndexOutOfBoundsException {@inheritDoc}
431 * @since 1.2
432 */
433 @Override
434 public synchronized StringBuffer delete(int start, int end) {
435 toStringCache = null;
436 super.delete(start, end);
437 return this;
438 }
439
440 /**
441 * @throws StringIndexOutOfBoundsException {@inheritDoc}
442 * @since 1.2
443 */
444 @Override
445 public synchronized StringBuffer deleteCharAt(int index) {
446 toStringCache = null;
447 super.deleteCharAt(index);
448 return this;
449 }
450
451 /**
452 * @throws StringIndexOutOfBoundsException {@inheritDoc}
453 * @since 1.2
454 */
455 @Override
456 public synchronized StringBuffer replace(int start, int end, String str) {
457 toStringCache = null;
458 super.replace(start, end, str);
459 return this;
460 }
461
462 /**
463 * @throws StringIndexOutOfBoundsException {@inheritDoc}
464 * @since 1.2
465 */
466 @Override
467 public synchronized String substring(int start) {
468 return substring(start, count);
469 }
470
471 /**
472 * @throws IndexOutOfBoundsException {@inheritDoc}
473 * @since 1.4
474 */
475 @Override
476 public synchronized CharSequence subSequence(int start, int end) {
477 return super.substring(start, end);
478 }
479
480 /**
481 * @throws StringIndexOutOfBoundsException {@inheritDoc}
482 * @since 1.2
483 */
484 @Override
485 public synchronized String substring(int start, int end) {
486 return super.substring(start, end);
487 }
488
489 /**
490 * @throws StringIndexOutOfBoundsException {@inheritDoc}
491 * @since 1.2
492 */
493 @Override
494 public synchronized StringBuffer insert(int index, char[] str, int offset,
495 int len)
496 {
497 toStringCache = null;
498 super.insert(index, str, offset, len);
499 return this;
500 }
501
502 /**
503 * @throws StringIndexOutOfBoundsException {@inheritDoc}
504 */
505 @Override
506 public synchronized StringBuffer insert(int offset, Object obj) {
507 toStringCache = null;
508 super.insert(offset, String.valueOf(obj));
509 return this;
510 }
511
512 /**
513 * @throws StringIndexOutOfBoundsException {@inheritDoc}
514 */
515 @Override
516 public synchronized StringBuffer insert(int offset, String str) {
517 toStringCache = null;
518 super.insert(offset, str);
519 return this;
520 }
521
522 /**
523 * @throws StringIndexOutOfBoundsException {@inheritDoc}
524 */
525 @Override
526 public synchronized StringBuffer insert(int offset, char[] str) {
527 toStringCache = null;
528 super.insert(offset, str);
529 return this;
530 }
531
532 /**
533 * @throws IndexOutOfBoundsException {@inheritDoc}
534 * @since 1.5
535 */
536 @Override
537 public StringBuffer insert(int dstOffset, CharSequence s) {
538 // Note, synchronization achieved via invocations of other StringBuffer methods
539 // after narrowing of s to specific type
540 // Ditto for toStringCache clearing
541 super.insert(dstOffset, s);
542 return this;
543 }
544
545 /**
546 * @throws IndexOutOfBoundsException {@inheritDoc}
547 * @since 1.5
548 */
549 @Override
550 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
551 int start, int end)
552 {
553 toStringCache = null;
554 super.insert(dstOffset, s, start, end);
555 return this;
556 }
557
558 /**
559 * @throws StringIndexOutOfBoundsException {@inheritDoc}
560 */
561 @Override
562 public StringBuffer insert(int offset, boolean b) {
563 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
564 // after conversion of b to String by super class method
565 // Ditto for toStringCache clearing
566 super.insert(offset, b);
567 return this;
568 }
569
570 /**
571 * @throws IndexOutOfBoundsException {@inheritDoc}
572 */
573 @Override
574 public synchronized StringBuffer insert(int offset, char c) {
575 toStringCache = null;
576 super.insert(offset, c);
577 return this;
578 }
579
580 /**
581 * @throws StringIndexOutOfBoundsException {@inheritDoc}
582 */
583 @Override
584 public StringBuffer insert(int offset, int i) {
585 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
586 // after conversion of i to String by super class method
587 // Ditto for toStringCache clearing
588 super.insert(offset, i);
589 return this;
590 }
591
592 /**
593 * @throws StringIndexOutOfBoundsException {@inheritDoc}
594 */
595 @Override
596 public StringBuffer insert(int offset, long l) {
597 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
598 // after conversion of l to String by super class method
599 // Ditto for toStringCache clearing
600 super.insert(offset, l);
601 return this;
602 }
603
604 /**
605 * @throws StringIndexOutOfBoundsException {@inheritDoc}
606 */
607 @Override
608 public StringBuffer insert(int offset, float f) {
609 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
610 // after conversion of f to String by super class method
611 // Ditto for toStringCache clearing
612 super.insert(offset, f);
613 return this;
614 }
615
616 /**
617 * @throws StringIndexOutOfBoundsException {@inheritDoc}
618 */
619 @Override
620 public StringBuffer insert(int offset, double d) {
621 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
622 // after conversion of d to String by super class method
623 // Ditto for toStringCache clearing
624 super.insert(offset, d);
625 return this;
626 }
627
628 /**
629 * @since 1.4
630 */
631 @Override
632 public int indexOf(String str) {
633 // Note, synchronization achieved via invocations of other StringBuffer methods
634 return super.indexOf(str);
635 }
636
637 /**
638 * @since 1.4
639 */
640 @Override
641 public synchronized int indexOf(String str, int fromIndex) {
642 return super.indexOf(str, fromIndex);
643 }
644
645 /**
646 * @since 1.4
647 */
648 @Override
649 public int lastIndexOf(String str) {
650 // Note, synchronization achieved via invocations of other StringBuffer methods
651 return lastIndexOf(str, count);
652 }
653
654 /**
655 * @since 1.4
656 */
657 @Override
658 public synchronized int lastIndexOf(String str, int fromIndex) {
659 return super.lastIndexOf(str, fromIndex);
660 }
661
662 /**
663 * @since 1.0.2
664 */
665 @Override
666 public synchronized StringBuffer reverse() {
667 toStringCache = null;
668 super.reverse();
669 return this;
670 }
671
672 @Override
673 public synchronized String toString() {
674 if (toStringCache == null) {
675 toStringCache = Arrays.copyOfRange(value, 0, count);
676 }
677 return new String(toStringCache, true);
678 }
679
680 /**
681 * Serializable fields for StringBuffer.
682 *
683 * @serialField value char[]
684 * The backing character array of this StringBuffer.
685 * @serialField count int
686 * The number of characters in this StringBuffer.
687 * @serialField shared boolean
688 * A flag indicating whether the backing array is shared.
689 * The value is ignored upon deserialization.
690 */
691 private static final java.io.ObjectStreamField[] serialPersistentFields =
692 {
693 new java.io.ObjectStreamField("value", char[].class),
694 new java.io.ObjectStreamField("count", Integer.TYPE),
695 new java.io.ObjectStreamField("shared", Boolean.TYPE),
696 };
697
698 /**
699 * readObject is called to restore the state of the StringBuffer from
700 * a stream.
701 */
702 private synchronized void writeObject(java.io.ObjectOutputStream s)
703 throws java.io.IOException {
704 java.io.ObjectOutputStream.PutField fields = s.putFields();
705 fields.put("value", value);
706 fields.put("count", count);
707 fields.put("shared", false);
708 s.writeFields();
709 }
710
711 /**
712 * readObject is called to restore the state of the StringBuffer from
713 * a stream.
714 */
715 private void readObject(java.io.ObjectInputStream s)
716 throws java.io.IOException, ClassNotFoundException {
717 java.io.ObjectInputStream.GetField fields = s.readFields();
718 value = (char[])fields.get("value", null);
719 count = fields.get("count", 0);
720 }
721 }