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 synchronized StringBuffer append(CharSequence s) {
339 toStringCache = null;
340 super.append(s);
341 return this;
342 }
343
344 /**
345 * @throws IndexOutOfBoundsException {@inheritDoc}
346 * @since 1.5
347 */
348 @Override
349 public synchronized StringBuffer append(CharSequence s, int start, int end)
350 {
351 toStringCache = null;
352 super.append(s, start, end);
353 return this;
354 }
355
356 @Override
357 public synchronized StringBuffer append(char[] str) {
358 toStringCache = null;
359 super.append(str);
360 return this;
361 }
362
363 /**
364 * @throws IndexOutOfBoundsException {@inheritDoc}
365 */
366 @Override
367 public synchronized StringBuffer append(char[] str, int offset, int len) {
368 toStringCache = null;
369 super.append(str, offset, len);
370 return this;
371 }
372
373 @Override
374 public synchronized StringBuffer append(boolean b) {
375 toStringCache = null;
376 super.append(b);
377 return this;
378 }
379
380 @Override
381 public synchronized StringBuffer append(char c) {
382 toStringCache = null;
383 super.append(c);
384 return this;
385 }
386
387 @Override
388 public synchronized StringBuffer append(int i) {
389 toStringCache = null;
390 super.append(i);
391 return this;
392 }
393
394 /**
395 * @since 1.5
396 */
397 @Override
398 public synchronized StringBuffer appendCodePoint(int codePoint) {
399 toStringCache = null;
400 super.appendCodePoint(codePoint);
401 return this;
402 }
403
404 @Override
405 public synchronized StringBuffer append(long lng) {
406 toStringCache = null;
407 super.append(lng);
408 return this;
409 }
410
411 @Override
412 public synchronized StringBuffer append(float f) {
413 toStringCache = null;
414 super.append(f);
415 return this;
416 }
417
418 @Override
419 public synchronized StringBuffer append(double d) {
420 toStringCache = null;
421 super.append(d);
422 return this;
423 }
424
425 /**
426 * @throws StringIndexOutOfBoundsException {@inheritDoc}
427 * @since 1.2
428 */
429 @Override
430 public synchronized StringBuffer delete(int start, int end) {
431 toStringCache = null;
432 super.delete(start, end);
433 return this;
434 }
435
436 /**
437 * @throws StringIndexOutOfBoundsException {@inheritDoc}
438 * @since 1.2
439 */
440 @Override
441 public synchronized StringBuffer deleteCharAt(int index) {
442 toStringCache = null;
443 super.deleteCharAt(index);
444 return this;
445 }
446
447 /**
448 * @throws StringIndexOutOfBoundsException {@inheritDoc}
449 * @since 1.2
450 */
451 @Override
452 public synchronized StringBuffer replace(int start, int end, String str) {
453 toStringCache = null;
454 super.replace(start, end, str);
455 return this;
456 }
457
458 /**
459 * @throws StringIndexOutOfBoundsException {@inheritDoc}
460 * @since 1.2
461 */
462 @Override
463 public synchronized String substring(int start) {
464 return substring(start, count);
465 }
466
467 /**
468 * @throws IndexOutOfBoundsException {@inheritDoc}
469 * @since 1.4
470 */
471 @Override
472 public synchronized CharSequence subSequence(int start, int end) {
473 return super.substring(start, end);
474 }
475
476 /**
477 * @throws StringIndexOutOfBoundsException {@inheritDoc}
478 * @since 1.2
479 */
480 @Override
481 public synchronized String substring(int start, int end) {
482 return super.substring(start, end);
483 }
484
485 /**
486 * @throws StringIndexOutOfBoundsException {@inheritDoc}
487 * @since 1.2
488 */
489 @Override
490 public synchronized StringBuffer insert(int index, char[] str, int offset,
491 int len)
492 {
493 toStringCache = null;
494 super.insert(index, str, offset, len);
495 return this;
496 }
497
498 /**
499 * @throws StringIndexOutOfBoundsException {@inheritDoc}
500 */
501 @Override
502 public synchronized StringBuffer insert(int offset, Object obj) {
503 toStringCache = null;
504 super.insert(offset, String.valueOf(obj));
505 return this;
506 }
507
508 /**
509 * @throws StringIndexOutOfBoundsException {@inheritDoc}
510 */
511 @Override
512 public synchronized StringBuffer insert(int offset, String str) {
513 toStringCache = null;
514 super.insert(offset, str);
515 return this;
516 }
517
518 /**
519 * @throws StringIndexOutOfBoundsException {@inheritDoc}
520 */
521 @Override
522 public synchronized StringBuffer insert(int offset, char[] str) {
523 toStringCache = null;
524 super.insert(offset, str);
525 return this;
526 }
527
528 /**
529 * @throws IndexOutOfBoundsException {@inheritDoc}
530 * @since 1.5
531 */
532 @Override
533 public StringBuffer insert(int dstOffset, CharSequence s) {
534 // Note, synchronization achieved via invocations of other StringBuffer methods
535 // after narrowing of s to specific type
536 // Ditto for toStringCache clearing
537 super.insert(dstOffset, s);
538 return this;
539 }
540
541 /**
542 * @throws IndexOutOfBoundsException {@inheritDoc}
543 * @since 1.5
544 */
545 @Override
546 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
547 int start, int end)
548 {
549 toStringCache = null;
550 super.insert(dstOffset, s, start, end);
551 return this;
552 }
553
554 /**
555 * @throws StringIndexOutOfBoundsException {@inheritDoc}
556 */
557 @Override
558 public StringBuffer insert(int offset, boolean b) {
559 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
560 // after conversion of b to String by super class method
561 // Ditto for toStringCache clearing
562 super.insert(offset, b);
563 return this;
564 }
565
566 /**
567 * @throws IndexOutOfBoundsException {@inheritDoc}
568 */
569 @Override
570 public synchronized StringBuffer insert(int offset, char c) {
571 toStringCache = null;
572 super.insert(offset, c);
573 return this;
574 }
575
576 /**
577 * @throws StringIndexOutOfBoundsException {@inheritDoc}
578 */
579 @Override
580 public StringBuffer insert(int offset, int i) {
581 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
582 // after conversion of i to String by super class method
583 // Ditto for toStringCache clearing
584 super.insert(offset, i);
585 return this;
586 }
587
588 /**
589 * @throws StringIndexOutOfBoundsException {@inheritDoc}
590 */
591 @Override
592 public StringBuffer insert(int offset, long l) {
593 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
594 // after conversion of l to String by super class method
595 // Ditto for toStringCache clearing
596 super.insert(offset, l);
597 return this;
598 }
599
600 /**
601 * @throws StringIndexOutOfBoundsException {@inheritDoc}
602 */
603 @Override
604 public StringBuffer insert(int offset, float f) {
605 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
606 // after conversion of f to String by super class method
607 // Ditto for toStringCache clearing
608 super.insert(offset, f);
609 return this;
610 }
611
612 /**
613 * @throws StringIndexOutOfBoundsException {@inheritDoc}
614 */
615 @Override
616 public StringBuffer insert(int offset, double d) {
617 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
618 // after conversion of d to String by super class method
619 // Ditto for toStringCache clearing
620 super.insert(offset, d);
621 return this;
622 }
623
624 /**
625 * @since 1.4
626 */
627 @Override
628 public int indexOf(String str) {
629 // Note, synchronization achieved via invocations of other StringBuffer methods
630 return super.indexOf(str);
631 }
632
633 /**
634 * @since 1.4
635 */
636 @Override
637 public synchronized int indexOf(String str, int fromIndex) {
638 return super.indexOf(str, fromIndex);
639 }
640
641 /**
642 * @since 1.4
643 */
644 @Override
645 public int lastIndexOf(String str) {
646 // Note, synchronization achieved via invocations of other StringBuffer methods
647 return lastIndexOf(str, count);
648 }
649
650 /**
651 * @since 1.4
652 */
653 @Override
654 public synchronized int lastIndexOf(String str, int fromIndex) {
655 return super.lastIndexOf(str, fromIndex);
656 }
657
658 /**
659 * @since JDK1.0.2
660 */
661 @Override
662 public synchronized StringBuffer reverse() {
663 toStringCache = null;
664 super.reverse();
665 return this;
666 }
667
668 @Override
669 public synchronized String toString() {
670 if (toStringCache == null) {
671 toStringCache = Arrays.copyOfRange(value, 0, count);
672 }
673 return new String(toStringCache, true);
674 }
675
676 /**
677 * Serializable fields for StringBuffer.
678 *
679 * @serialField value char[]
680 * The backing character array of this StringBuffer.
681 * @serialField count int
682 * The number of characters in this StringBuffer.
683 * @serialField shared boolean
684 * A flag indicating whether the backing array is shared.
685 * The value is ignored upon deserialization.
686 */
687 private static final java.io.ObjectStreamField[] serialPersistentFields =
688 {
689 new java.io.ObjectStreamField("value", char[].class),
690 new java.io.ObjectStreamField("count", Integer.TYPE),
691 new java.io.ObjectStreamField("shared", Boolean.TYPE),
692 };
693
694 /**
695 * readObject is called to restore the state of the StringBuffer from
696 * a stream.
697 */
698 private synchronized void writeObject(java.io.ObjectOutputStream s)
699 throws java.io.IOException {
700 java.io.ObjectOutputStream.PutField fields = s.putFields();
701 fields.put("value", value);
702 fields.put("count", count);
703 fields.put("shared", false);
704 s.writeFields();
705 }
706
707 /**
708 * readObject is called to restore the state of the StringBuffer from
709 * a stream.
710 */
711 private void readObject(java.io.ObjectInputStream s)
712 throws java.io.IOException, ClassNotFoundException {
713 java.io.ObjectInputStream.GetField fields = s.readFields();
714 value = (char[])fields.get("value", null);
715 count = fields.get("count", 0);
716 }
717 }