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 JDK1.0
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 * @since 1.5
210 */
211 @Override
212 public synchronized int codePointAt(int index) {
213 return super.codePointAt(index);
214 }
215
216 /**
217 * @since 1.5
218 */
219 @Override
220 public synchronized int codePointBefore(int index) {
221 return super.codePointBefore(index);
222 }
223
224 /**
225 * @since 1.5
226 */
227 @Override
228 public synchronized int codePointCount(int beginIndex, int endIndex) {
229 return super.codePointCount(beginIndex, endIndex);
230 }
231
232 /**
233 * @since 1.5
234 */
235 @Override
236 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
237 return super.offsetByCodePoints(index, codePointOffset);
238 }
239
240 /**
241 * @throws IndexOutOfBoundsException {@inheritDoc}
242 */
243 @Override
244 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
245 int dstBegin)
246 {
247 super.getChars(srcBegin, srcEnd, dst, dstBegin);
248 }
249
250 /**
251 * @throws IndexOutOfBoundsException {@inheritDoc}
252 * @see #length()
253 */
254 @Override
255 public synchronized void setCharAt(int index, char ch) {
256 if ((index < 0) || (index >= count))
257 throw new StringIndexOutOfBoundsException(index);
258 toStringCache = null;
259 value[index] = ch;
260 }
261
262 @Override
263 public synchronized StringBuffer append(Object obj) {
264 toStringCache = null;
265 super.append(String.valueOf(obj));
266 return this;
267 }
268
269 @Override
270 public synchronized StringBuffer append(String str) {
271 toStringCache = null;
272 super.append(str);
273 return this;
274 }
275
276 /**
277 * Appends the specified {@code StringBuffer} to this sequence.
278 * <p>
279 * The characters of the {@code StringBuffer} argument are appended,
280 * in order, to the contents of this {@code StringBuffer}, increasing the
281 * length of this {@code StringBuffer} by the length of the argument.
282 * If {@code sb} is {@code null}, then the four characters
283 * {@code "null"} are appended to this {@code StringBuffer}.
284 * <p>
285 * Let <i>n</i> be the length of the old character sequence, the one
286 * contained in the {@code StringBuffer} just prior to execution of the
287 * {@code append} method. Then the character at index <i>k</i> in
288 * the new character sequence is equal to the character at index <i>k</i>
289 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
290 * otherwise, it is equal to the character at index <i>k-n</i> in the
291 * argument {@code sb}.
292 * <p>
293 * This method synchronizes on {@code this}, the destination
294 * object, but does not synchronize on the source ({@code sb}).
295 *
296 * @param sb the {@code StringBuffer} to append.
297 * @return a reference to this object.
298 * @since 1.4
299 */
300 public synchronized StringBuffer append(StringBuffer sb) {
301 toStringCache = null;
302 super.append(sb);
303 return this;
304 }
305
306 /**
307 * @since 1.8
308 */
309 @Override
310 synchronized StringBuffer append(AbstractStringBuilder asb) {
311 toStringCache = null;
312 super.append(asb);
313 return this;
314 }
315
316 /**
317 * Appends the specified {@code CharSequence} to this
318 * sequence.
319 * <p>
320 * The characters of the {@code CharSequence} argument are appended,
321 * in order, increasing the length of this sequence by the length of the
322 * argument.
323 *
324 * <p>The result of this method is exactly the same as if it were an
325 * invocation of this.append(s, 0, s.length());
326 *
327 * <p>This method synchronizes on {@code this}, the destination
328 * object, but does not synchronize on the source ({@code s}).
329 *
330 * <p>If {@code s} is {@code null}, then the four characters
331 * {@code "null"} are appended.
332 *
333 * @param s the {@code CharSequence} to append.
334 * @return a reference to this object.
335 * @since 1.5
336 */
337 @Override
338 public StringBuffer append(CharSequence s) {
339 // Note, synchronization achieved via invocations of other StringBuffer methods after
340 // narrowing of s to specific type
341 // Ditto for toStringCache clearing
342 super.append(s);
343 return this;
344 }
345
346 /**
347 * @throws IndexOutOfBoundsException {@inheritDoc}
348 * @since 1.5
349 */
350 @Override
351 public synchronized StringBuffer append(CharSequence s, int start, int end)
352 {
353 toStringCache = null;
354 super.append(s, start, end);
355 return this;
356 }
357
358 @Override
359 public synchronized StringBuffer append(char[] str) {
360 toStringCache = null;
361 super.append(str);
362 return this;
363 }
364
365 /**
366 * @throws IndexOutOfBoundsException {@inheritDoc}
367 */
368 @Override
369 public synchronized StringBuffer append(char[] str, int offset, int len) {
370 toStringCache = null;
371 super.append(str, offset, len);
372 return this;
373 }
374
375 @Override
376 public synchronized StringBuffer append(boolean b) {
377 toStringCache = null;
378 super.append(b);
379 return this;
380 }
381
382 @Override
383 public synchronized StringBuffer append(char c) {
384 toStringCache = null;
385 super.append(c);
386 return this;
387 }
388
389 @Override
390 public synchronized StringBuffer append(int i) {
391 toStringCache = null;
392 super.append(i);
393 return this;
394 }
395
396 /**
397 * @since 1.5
398 */
399 @Override
400 public synchronized StringBuffer appendCodePoint(int codePoint) {
401 toStringCache = null;
402 super.appendCodePoint(codePoint);
403 return this;
404 }
405
406 @Override
407 public synchronized StringBuffer append(long lng) {
408 toStringCache = null;
409 super.append(lng);
410 return this;
411 }
412
413 @Override
414 public synchronized StringBuffer append(float f) {
415 toStringCache = null;
416 super.append(f);
417 return this;
418 }
419
420 @Override
421 public synchronized StringBuffer append(double d) {
422 toStringCache = null;
423 super.append(d);
424 return this;
425 }
426
427 /**
428 * @throws StringIndexOutOfBoundsException {@inheritDoc}
429 * @since 1.2
430 */
431 @Override
432 public synchronized StringBuffer delete(int start, int end) {
433 toStringCache = null;
434 super.delete(start, end);
435 return this;
436 }
437
438 /**
439 * @throws StringIndexOutOfBoundsException {@inheritDoc}
440 * @since 1.2
441 */
442 @Override
443 public synchronized StringBuffer deleteCharAt(int index) {
444 toStringCache = null;
445 super.deleteCharAt(index);
446 return this;
447 }
448
449 /**
450 * @throws StringIndexOutOfBoundsException {@inheritDoc}
451 * @since 1.2
452 */
453 @Override
454 public synchronized StringBuffer replace(int start, int end, String str) {
455 toStringCache = null;
456 super.replace(start, end, str);
457 return this;
458 }
459
460 /**
461 * @throws StringIndexOutOfBoundsException {@inheritDoc}
462 * @since 1.2
463 */
464 @Override
465 public synchronized String substring(int start) {
466 return substring(start, count);
467 }
468
469 /**
470 * @throws IndexOutOfBoundsException {@inheritDoc}
471 * @since 1.4
472 */
473 @Override
474 public synchronized CharSequence subSequence(int start, int end) {
475 return super.substring(start, end);
476 }
477
478 /**
479 * @throws StringIndexOutOfBoundsException {@inheritDoc}
480 * @since 1.2
481 */
482 @Override
483 public synchronized String substring(int start, int end) {
484 return super.substring(start, end);
485 }
486
487 /**
488 * @throws StringIndexOutOfBoundsException {@inheritDoc}
489 * @since 1.2
490 */
491 @Override
492 public synchronized StringBuffer insert(int index, char[] str, int offset,
493 int len)
494 {
495 toStringCache = null;
496 super.insert(index, str, offset, len);
497 return this;
498 }
499
500 /**
501 * @throws StringIndexOutOfBoundsException {@inheritDoc}
502 */
503 @Override
504 public synchronized StringBuffer insert(int offset, Object obj) {
505 toStringCache = null;
506 super.insert(offset, String.valueOf(obj));
507 return this;
508 }
509
510 /**
511 * @throws StringIndexOutOfBoundsException {@inheritDoc}
512 */
513 @Override
514 public synchronized StringBuffer insert(int offset, String str) {
515 toStringCache = null;
516 super.insert(offset, str);
517 return this;
518 }
519
520 /**
521 * @throws StringIndexOutOfBoundsException {@inheritDoc}
522 */
523 @Override
524 public synchronized StringBuffer insert(int offset, char[] str) {
525 toStringCache = null;
526 super.insert(offset, str);
527 return this;
528 }
529
530 /**
531 * @throws IndexOutOfBoundsException {@inheritDoc}
532 * @since 1.5
533 */
534 @Override
535 public StringBuffer insert(int dstOffset, CharSequence s) {
536 // Note, synchronization achieved via invocations of other StringBuffer methods
537 // after narrowing of s to specific type
538 // Ditto for toStringCache clearing
539 super.insert(dstOffset, s);
540 return this;
541 }
542
543 /**
544 * @throws IndexOutOfBoundsException {@inheritDoc}
545 * @since 1.5
546 */
547 @Override
548 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
549 int start, int end)
550 {
551 toStringCache = null;
552 super.insert(dstOffset, s, start, end);
553 return this;
554 }
555
556 /**
557 * @throws StringIndexOutOfBoundsException {@inheritDoc}
558 */
559 @Override
560 public StringBuffer insert(int offset, boolean b) {
561 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
562 // after conversion of b to String by super class method
563 // Ditto for toStringCache clearing
564 super.insert(offset, b);
565 return this;
566 }
567
568 /**
569 * @throws IndexOutOfBoundsException {@inheritDoc}
570 */
571 @Override
572 public synchronized StringBuffer insert(int offset, char c) {
573 toStringCache = null;
574 super.insert(offset, c);
575 return this;
576 }
577
578 /**
579 * @throws StringIndexOutOfBoundsException {@inheritDoc}
580 */
581 @Override
582 public StringBuffer insert(int offset, int i) {
583 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
584 // after conversion of i to String by super class method
585 // Ditto for toStringCache clearing
586 super.insert(offset, i);
587 return this;
588 }
589
590 /**
591 * @throws StringIndexOutOfBoundsException {@inheritDoc}
592 */
593 @Override
594 public StringBuffer insert(int offset, long l) {
595 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
596 // after conversion of l to String by super class method
597 // Ditto for toStringCache clearing
598 super.insert(offset, l);
599 return this;
600 }
601
602 /**
603 * @throws StringIndexOutOfBoundsException {@inheritDoc}
604 */
605 @Override
606 public StringBuffer insert(int offset, float f) {
607 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
608 // after conversion of f to String by super class method
609 // Ditto for toStringCache clearing
610 super.insert(offset, f);
611 return this;
612 }
613
614 /**
615 * @throws StringIndexOutOfBoundsException {@inheritDoc}
616 */
617 @Override
618 public StringBuffer insert(int offset, double d) {
619 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
620 // after conversion of d to String by super class method
621 // Ditto for toStringCache clearing
622 super.insert(offset, d);
623 return this;
624 }
625
626 /**
627 * @since 1.4
628 */
629 @Override
630 public int indexOf(String str) {
631 // Note, synchronization achieved via invocations of other StringBuffer methods
632 return super.indexOf(str);
633 }
634
635 /**
636 * @since 1.4
637 */
638 @Override
639 public synchronized int indexOf(String str, int fromIndex) {
640 return super.indexOf(str, fromIndex);
641 }
642
643 /**
644 * @since 1.4
645 */
646 @Override
647 public int lastIndexOf(String str) {
648 // Note, synchronization achieved via invocations of other StringBuffer methods
649 return lastIndexOf(str, count);
650 }
651
652 /**
653 * @since 1.4
654 */
655 @Override
656 public synchronized int lastIndexOf(String str, int fromIndex) {
657 return super.lastIndexOf(str, fromIndex);
658 }
659
660 /**
661 * @since JDK1.0.2
662 */
663 @Override
664 public synchronized StringBuffer reverse() {
665 toStringCache = null;
666 super.reverse();
667 return this;
668 }
669
670 @Override
671 public synchronized String toString() {
672 if (toStringCache == null) {
673 toStringCache = Arrays.copyOfRange(value, 0, count);
674 }
675 return new String(toStringCache, true);
676 }
677
678 /**
679 * Serializable fields for StringBuffer.
680 *
681 * @serialField value char[]
682 * The backing character array of this StringBuffer.
683 * @serialField count int
684 * The number of characters in this StringBuffer.
685 * @serialField shared boolean
686 * A flag indicating whether the backing array is shared.
687 * The value is ignored upon deserialization.
688 */
689 private static final java.io.ObjectStreamField[] serialPersistentFields =
690 {
691 new java.io.ObjectStreamField("value", char[].class),
692 new java.io.ObjectStreamField("count", Integer.TYPE),
693 new java.io.ObjectStreamField("shared", Boolean.TYPE),
694 };
695
696 /**
697 * readObject is called to restore the state of the StringBuffer from
698 * a stream.
699 */
700 private synchronized void writeObject(java.io.ObjectOutputStream s)
701 throws java.io.IOException {
702 java.io.ObjectOutputStream.PutField fields = s.putFields();
703 fields.put("value", value);
704 fields.put("count", count);
705 fields.put("shared", false);
706 s.writeFields();
707 }
708
709 /**
710 * readObject is called to restore the state of the StringBuffer from
711 * a stream.
712 */
713 private void readObject(java.io.ObjectInputStream s)
714 throws java.io.IOException, ClassNotFoundException {
715 java.io.ObjectInputStream.GetField fields = s.readFields();
716 value = (char[])fields.get("value", null);
717 count = fields.get("count", 0);
718 }
719 }