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
29 /**
30 * A thread-safe, mutable sequence of characters.
31 * A string buffer is like a {@link String}, but can be modified. At any
32 * point in time it contains some particular sequence of characters, but
33 * the length and content of the sequence can be changed through certain
34 * method calls.
35 * <p>
36 * String buffers are safe for use by multiple threads. The methods
37 * are synchronized where necessary so that all the operations on any
38 * particular instance behave as if they occur in some serial order
39 * that is consistent with the order of the method calls made by each of
40 * the individual threads involved.
41 * <p>
42 * The principal operations on a {@code StringBuffer} are the
43 * {@code append} and {@code insert} methods, which are
44 * overloaded so as to accept data of any type. Each effectively
45 * converts a given datum to a string and then appends or inserts the
46 * characters of that string to the string buffer. The
47 * {@code append} method always adds these characters at the end
48 * of the buffer; the {@code insert} method adds the characters at
49 * a specified point.
50 * <p>
51 * For example, if {@code z} refers to a string buffer object
52 * whose current contents are {@code "start"}, then
53 * the method call {@code z.append("le")} would cause the string
54 * buffer to contain {@code "startle"}, whereas
55 * {@code z.insert(4, "le")} would alter the string buffer to
56 * contain {@code "starlet"}.
57 * <p>
58 * In general, if sb refers to an instance of a {@code StringBuffer},
59 * then {@code sb.append(x)} has the same effect as
60 * {@code sb.insert(sb.length(), x)}.
61 * <p>
62 * Whenever an operation occurs involving a source sequence (such as
63 * appending or inserting from a source sequence), this class synchronizes
64 * only on the string buffer performing the operation, not on the source.
65 * Note that while {@code StringBuffer} is designed to be safe to use
66 * concurrently from multiple threads, if the constructor or the
67 * {@code append} or {@code insert} operation is passed a source sequence
68 * that is shared across threads, the calling code must ensure
69 * that the operation has a consistent and unchanging view of the source
70 * sequence for the duration of the operation.
71 * This could be satisfied by the caller holding a lock during the
72 * operation's call, by using an immutable source sequence, or by not
73 * sharing the source sequence across threads.
74 * <p>
75 * Every string buffer has a capacity. As long as the length of the
76 * character sequence contained in the string buffer does not exceed
77 * the capacity, it is not necessary to allocate a new internal
78 * buffer array. If the internal buffer overflows, it is
79 * automatically made larger.
80 * <p>
81 * Unless otherwise noted, passing a {@code null} argument to a constructor
82 * or method in this class will cause a {@link NullPointerException} to be
83 * thrown.
84 * <p>
85 * As of release JDK 5, this class has been supplemented with an equivalent
86 * class designed for use by a single thread, {@link StringBuilder}. The
87 * {@code StringBuilder} class should generally be used in preference to
88 * this one, as it supports all of the same operations but it is faster, as
89 * it performs no synchronization.
90 *
91 * @author Arthur van Hoff
92 * @see java.lang.StringBuilder
93 * @see java.lang.String
94 * @since JDK1.0
95 */
96 public final class StringBuffer
97 extends AbstractStringBuilder
98 implements java.io.Serializable, CharSequence
99 {
100
101 /**
102 * A cache of the last value returned by toString. Cleared
103 * whenever the StringBuffer is modified.
104 */
105 private transient String toStringCache;
106
107 /** use serialVersionUID from JDK 1.0.2 for interoperability */
108 static final long serialVersionUID = 3388685877147921107L;
109
110 /**
111 * Constructs a string buffer with no characters in it and an
112 * initial capacity of 16 characters.
113 */
114 public StringBuffer() {
115 super(16);
116 }
117
118 /**
119 * Constructs a string buffer with no characters in it and
120 * the specified initial capacity.
121 *
122 * @param capacity the initial capacity.
123 * @exception NegativeArraySizeException if the {@code capacity}
124 * argument is less than {@code 0}.
125 */
126 public StringBuffer(int capacity) {
127 super(capacity);
128 }
129
130 /**
131 * Constructs a string buffer initialized to the contents of the
132 * specified string. The initial capacity of the string buffer is
133 * {@code 16} plus the length of the string argument.
134 *
135 * @param str the initial contents of the buffer.
136 */
137 public StringBuffer(String str) {
138 super(str.length() + 16);
139 append(str);
140 }
141
142 /**
143 * Constructs a string buffer that contains the same characters
144 * as the specified {@code CharSequence}. The initial capacity of
145 * the string buffer is {@code 16} plus the length of the
146 * {@code CharSequence} argument.
147 * <p>
148 * If the length of the specified {@code CharSequence} is
149 * less than or equal to zero, then an empty buffer of capacity
150 * {@code 16} is returned.
151 *
152 * @param seq the sequence to copy.
153 * @since 1.5
154 */
155 public StringBuffer(CharSequence seq) {
156 this(seq.length() + 16);
157 append(seq);
158 }
159
160 @Override
161 public synchronized int length() {
162 return count;
163 }
164
165 @Override
166 public synchronized int capacity() {
167 return value.length;
168 }
169
170
171 @Override
172 public synchronized void ensureCapacity(int minimumCapacity) {
173 if (minimumCapacity > value.length) {
174 expandCapacity(minimumCapacity);
175 }
176 }
177
178 /**
179 * @since 1.5
180 */
181 @Override
182 public synchronized void trimToSize() {
183 super.trimToSize();
184 }
185
186 /**
187 * @throws IndexOutOfBoundsException {@inheritDoc}
188 * @see #length()
189 */
190 @Override
191 public synchronized void setLength(int newLength) {
192 super.setLength(newLength);
193 toStringCache = null;
194 }
195
196 /**
197 * @throws IndexOutOfBoundsException {@inheritDoc}
198 * @see #length()
199 */
200 @Override
201 public synchronized char charAt(int index) {
202 if ((index < 0) || (index >= count))
203 throw new StringIndexOutOfBoundsException(index);
204 return value[index];
205 }
206
207 /**
208 * @since 1.5
209 */
210 @Override
211 public synchronized int codePointAt(int index) {
212 return super.codePointAt(index);
213 }
214
215 /**
216 * @since 1.5
217 */
218 @Override
219 public synchronized int codePointBefore(int index) {
220 return super.codePointBefore(index);
221 }
222
223 /**
224 * @since 1.5
225 */
226 @Override
227 public synchronized int codePointCount(int beginIndex, int endIndex) {
228 return super.codePointCount(beginIndex, endIndex);
229 }
230
231 /**
232 * @since 1.5
233 */
234 @Override
235 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
236 return super.offsetByCodePoints(index, codePointOffset);
237 }
238
239 /**
240 * @throws IndexOutOfBoundsException {@inheritDoc}
241 */
242 @Override
243 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
244 int dstBegin)
245 {
246 super.getChars(srcBegin, srcEnd, dst, dstBegin);
247 }
248
249 /**
250 * @throws IndexOutOfBoundsException {@inheritDoc}
251 * @see #length()
252 */
253 @Override
254 public synchronized void setCharAt(int index, char ch) {
255 if ((index < 0) || (index >= count))
256 throw new StringIndexOutOfBoundsException(index);
257 value[index] = ch;
258 toStringCache = null;
259 }
260
261 @Override
262 public synchronized StringBuffer append(Object obj) {
263 super.append(String.valueOf(obj));
264 toStringCache = null;
265 return this;
266 }
267
268 @Override
269 public synchronized StringBuffer append(String str) {
270 super.append(str);
271 toStringCache = null;
272 return this;
273 }
274
275 /**
276 * Appends the specified {@code StringBuffer} to this sequence.
277 * <p>
278 * The characters of the {@code StringBuffer} argument are appended,
279 * in order, to the contents of this {@code StringBuffer}, increasing the
280 * length of this {@code StringBuffer} by the length of the argument.
281 * If {@code sb} is {@code null}, then the four characters
282 * {@code "null"} are appended to this {@code StringBuffer}.
283 * <p>
284 * Let <i>n</i> be the length of the old character sequence, the one
285 * contained in the {@code StringBuffer} just prior to execution of the
286 * {@code append} method. Then the character at index <i>k</i> in
287 * the new character sequence is equal to the character at index <i>k</i>
288 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
289 * otherwise, it is equal to the character at index <i>k-n</i> in the
290 * argument {@code sb}.
291 * <p>
292 * This method synchronizes on {@code this}, the destination
293 * object, but does not synchronize on the source ({@code sb}).
294 *
295 * @param sb the {@code StringBuffer} to append.
296 * @return a reference to this object.
297 * @since 1.4
298 */
299 public synchronized StringBuffer append(StringBuffer sb) {
300 super.append(sb);
301 toStringCache = null;
302 return this;
303 }
304
305 /**
306 * @since 1.8
307 */
308 @Override
309 synchronized StringBuffer append(AbstractStringBuilder asb) {
310 super.append(asb);
311 toStringCache = null;
312 return this;
313 }
314
315 /**
316 * Appends the specified {@code CharSequence} to this
317 * sequence.
318 * <p>
319 * The characters of the {@code CharSequence} argument are appended,
320 * in order, increasing the length of this sequence by the length of the
321 * argument.
322 *
323 * <p>The result of this method is exactly the same as if it were an
324 * invocation of this.append(s, 0, s.length());
325 *
326 * <p>This method synchronizes on {@code this}, the destination
327 * object, but does not synchronize on the source ({@code s}).
328 *
329 * <p>If {@code s} is {@code null}, then the four characters
330 * {@code "null"} are appended.
331 *
332 * @param s the {@code CharSequence} to append.
333 * @return a reference to this object.
334 * @since 1.5
335 */
336 @Override
337 public StringBuffer append(CharSequence s) {
338 // Note, synchronization achieved via invocations of other StringBuffer methods after
339 // narrowing of s to specific type
340 // Ditto for toStringCache clearing
341 super.append(s);
342 return this;
343 }
344
345 /**
346 * @throws IndexOutOfBoundsException {@inheritDoc}
347 * @since 1.5
348 */
349 @Override
350 public synchronized StringBuffer append(CharSequence s, int start, int end)
351 {
352 super.append(s, start, end);
353 toStringCache = null;
354 return this;
355 }
356
357 @Override
358 public synchronized StringBuffer append(char[] str) {
359 super.append(str);
360 toStringCache = null;
361 return this;
362 }
363
364 /**
365 * @throws IndexOutOfBoundsException {@inheritDoc}
366 */
367 @Override
368 public synchronized StringBuffer append(char[] str, int offset, int len) {
369 super.append(str, offset, len);
370 toStringCache = null;
371 return this;
372 }
373
374 @Override
375 public synchronized StringBuffer append(boolean b) {
376 super.append(b);
377 toStringCache = null;
378 return this;
379 }
380
381 @Override
382 public synchronized StringBuffer append(char c) {
383 super.append(c);
384 toStringCache = null;
385 return this;
386 }
387
388 @Override
389 public synchronized StringBuffer append(int i) {
390 super.append(i);
391 toStringCache = null;
392 return this;
393 }
394
395 /**
396 * @since 1.5
397 */
398 @Override
399 public synchronized StringBuffer appendCodePoint(int codePoint) {
400 super.appendCodePoint(codePoint);
401 toStringCache = null;
402 return this;
403 }
404
405 @Override
406 public synchronized StringBuffer append(long lng) {
407 super.append(lng);
408 toStringCache = null;
409 return this;
410 }
411
412 @Override
413 public synchronized StringBuffer append(float f) {
414 super.append(f);
415 toStringCache = null;
416 return this;
417 }
418
419 @Override
420 public synchronized StringBuffer append(double d) {
421 super.append(d);
422 toStringCache = null;
423 return this;
424 }
425
426 /**
427 * @throws StringIndexOutOfBoundsException {@inheritDoc}
428 * @since 1.2
429 */
430 @Override
431 public synchronized StringBuffer delete(int start, int end) {
432 super.delete(start, end);
433 toStringCache = null;
434 return this;
435 }
436
437 /**
438 * @throws StringIndexOutOfBoundsException {@inheritDoc}
439 * @since 1.2
440 */
441 @Override
442 public synchronized StringBuffer deleteCharAt(int index) {
443 super.deleteCharAt(index);
444 toStringCache = null;
445 return this;
446 }
447
448 /**
449 * @throws StringIndexOutOfBoundsException {@inheritDoc}
450 * @since 1.2
451 */
452 @Override
453 public synchronized StringBuffer replace(int start, int end, String str) {
454 super.replace(start, end, str);
455 toStringCache = null;
456 return this;
457 }
458
459 /**
460 * @throws StringIndexOutOfBoundsException {@inheritDoc}
461 * @since 1.2
462 */
463 @Override
464 public synchronized String substring(int start) {
465 return substring(start, count);
466 }
467
468 /**
469 * @throws IndexOutOfBoundsException {@inheritDoc}
470 * @since 1.4
471 */
472 @Override
473 public synchronized CharSequence subSequence(int start, int end) {
474 return super.substring(start, end);
475 }
476
477 /**
478 * @throws StringIndexOutOfBoundsException {@inheritDoc}
479 * @since 1.2
480 */
481 @Override
482 public synchronized String substring(int start, int end) {
483 return super.substring(start, end);
484 }
485
486 /**
487 * @throws StringIndexOutOfBoundsException {@inheritDoc}
488 * @since 1.2
489 */
490 @Override
491 public synchronized StringBuffer insert(int index, char[] str, int offset,
492 int len)
493 {
494 super.insert(index, str, offset, len);
495 toStringCache = null;
496 return this;
497 }
498
499 /**
500 * @throws StringIndexOutOfBoundsException {@inheritDoc}
501 */
502 @Override
503 public synchronized StringBuffer insert(int offset, Object obj) {
504 super.insert(offset, String.valueOf(obj));
505 toStringCache = null;
506 return this;
507 }
508
509 /**
510 * @throws StringIndexOutOfBoundsException {@inheritDoc}
511 */
512 @Override
513 public synchronized StringBuffer insert(int offset, String str) {
514 super.insert(offset, str);
515 toStringCache = null;
516 return this;
517 }
518
519 /**
520 * @throws StringIndexOutOfBoundsException {@inheritDoc}
521 */
522 @Override
523 public synchronized StringBuffer insert(int offset, char[] str) {
524 super.insert(offset, str);
525 toStringCache = null;
526 return this;
527 }
528
529 /**
530 * @throws IndexOutOfBoundsException {@inheritDoc}
531 * @since 1.5
532 */
533 @Override
534 public StringBuffer insert(int dstOffset, CharSequence s) {
535 // Note, synchronization achieved via invocations of other StringBuffer methods
536 // after narrowing of s to specific type
537 // Ditto for toStringCache clearing
538 super.insert(dstOffset, s);
539 return this;
540 }
541
542 /**
543 * @throws IndexOutOfBoundsException {@inheritDoc}
544 * @since 1.5
545 */
546 @Override
547 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
548 int start, int end)
549 {
550 super.insert(dstOffset, s, start, end);
551 toStringCache = null;
552 return this;
553 }
554
555 /**
556 * @throws StringIndexOutOfBoundsException {@inheritDoc}
557 */
558 @Override
559 public StringBuffer insert(int offset, boolean b) {
560 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
561 // after conversion of b to String by super class method
562 // Ditto for toStringCache clearing
563 super.insert(offset, b);
564 return this;
565 }
566
567 /**
568 * @throws IndexOutOfBoundsException {@inheritDoc}
569 */
570 @Override
571 public synchronized StringBuffer insert(int offset, char c) {
572 super.insert(offset, c);
573 toStringCache = null;
574 return this;
575 }
576
577 /**
578 * @throws StringIndexOutOfBoundsException {@inheritDoc}
579 */
580 @Override
581 public StringBuffer insert(int offset, int i) {
582 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
583 // after conversion of i to String by super class method
584 // Ditto for toStringCache clearing
585 super.insert(offset, i);
586 return this;
587 }
588
589 /**
590 * @throws StringIndexOutOfBoundsException {@inheritDoc}
591 */
592 @Override
593 public StringBuffer insert(int offset, long l) {
594 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
595 // after conversion of l to String by super class method
596 // Ditto for toStringCache clearing
597 super.insert(offset, l);
598 return this;
599 }
600
601 /**
602 * @throws StringIndexOutOfBoundsException {@inheritDoc}
603 */
604 @Override
605 public StringBuffer insert(int offset, float f) {
606 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
607 // after conversion of f to String by super class method
608 // Ditto for toStringCache clearing
609 super.insert(offset, f);
610 return this;
611 }
612
613 /**
614 * @throws StringIndexOutOfBoundsException {@inheritDoc}
615 */
616 @Override
617 public StringBuffer insert(int offset, double d) {
618 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
619 // after conversion of d to String by super class method
620 // Ditto for toStringCache clearing
621 super.insert(offset, d);
622 return this;
623 }
624
625 /**
626 * @since 1.4
627 */
628 @Override
629 public int indexOf(String str) {
630 // Note, synchronization achieved via invocations of other StringBuffer methods
631 return super.indexOf(str);
632 }
633
634 /**
635 * @since 1.4
636 */
637 @Override
638 public synchronized int indexOf(String str, int fromIndex) {
639 return super.indexOf(str, fromIndex);
640 }
641
642 /**
643 * @since 1.4
644 */
645 @Override
646 public int lastIndexOf(String str) {
647 // Note, synchronization achieved via invocations of other StringBuffer methods
648 return lastIndexOf(str, count);
649 }
650
651 /**
652 * @since 1.4
653 */
654 @Override
655 public synchronized int lastIndexOf(String str, int fromIndex) {
656 return super.lastIndexOf(str, fromIndex);
657 }
658
659 /**
660 * @since JDK1.0.2
661 */
662 @Override
663 public synchronized StringBuffer reverse() {
664 super.reverse();
665 toStringCache = null;
666 return this;
667 }
668
669 @Override
670 public synchronized String toString() {
671 if (toStringCache == null) {
672 toStringCache = new String(value, 0, count);
673 return toStringCache;
674 } else {
675 return new String(toStringCache);
676 }
677 }
678
679 /**
680 * Serializable fields for StringBuffer.
681 *
682 * @serialField value char[]
683 * The backing character array of this StringBuffer.
684 * @serialField count int
685 * The number of characters in this StringBuffer.
686 * @serialField shared boolean
687 * A flag indicating whether the backing array is shared.
688 * The value is ignored upon deserialization.
689 */
690 private static final java.io.ObjectStreamField[] serialPersistentFields =
691 {
692 new java.io.ObjectStreamField("value", char[].class),
693 new java.io.ObjectStreamField("count", Integer.TYPE),
694 new java.io.ObjectStreamField("shared", Boolean.TYPE),
695 };
696
697 /**
698 * readObject is called to restore the state of the StringBuffer from
699 * a stream.
700 */
701 private synchronized void writeObject(java.io.ObjectOutputStream s)
702 throws java.io.IOException {
703 java.io.ObjectOutputStream.PutField fields = s.putFields();
704 fields.put("value", value);
705 fields.put("count", count);
706 fields.put("shared", false);
707 s.writeFields();
708 }
709
710 /**
711 * readObject is called to restore the state of the StringBuffer from
712 * a stream.
713 */
714 private void readObject(java.io.ObjectInputStream s)
715 throws java.io.IOException, ClassNotFoundException {
716 java.io.ObjectInputStream.GetField fields = s.readFields();
717 value = (char[])fields.get("value", null);
718 count = fields.get("count", 0);
719 }
720 }