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 super.ensureCapacity(minimumCapacity);
175 }
176
177 /**
178 * @since 1.5
179 */
180 @Override
181 public synchronized void trimToSize() {
182 super.trimToSize();
183 }
184
185 /**
186 * @throws IndexOutOfBoundsException {@inheritDoc}
187 * @see #length()
188 */
189 @Override
190 public synchronized void setLength(int newLength) {
191 toStringCache = null;
192 super.setLength(newLength);
193 }
194
195 /**
196 * @throws IndexOutOfBoundsException {@inheritDoc}
197 * @see #length()
198 */
199 @Override
200 public synchronized char charAt(int index) {
201 if ((index < 0) || (index >= count))
202 throw new StringIndexOutOfBoundsException(index);
203 return value[index];
204 }
205
206 /**
207 * @since 1.5
208 */
209 @Override
210 public synchronized int codePointAt(int index) {
211 return super.codePointAt(index);
212 }
213
214 /**
215 * @since 1.5
216 */
217 @Override
218 public synchronized int codePointBefore(int index) {
219 return super.codePointBefore(index);
220 }
221
222 /**
223 * @since 1.5
224 */
225 @Override
226 public synchronized int codePointCount(int beginIndex, int endIndex) {
227 return super.codePointCount(beginIndex, endIndex);
228 }
229
230 /**
231 * @since 1.5
232 */
233 @Override
234 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
235 return super.offsetByCodePoints(index, codePointOffset);
236 }
237
238 /**
239 * @throws IndexOutOfBoundsException {@inheritDoc}
240 */
241 @Override
242 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
243 int dstBegin)
244 {
245 super.getChars(srcBegin, srcEnd, dst, dstBegin);
246 }
247
248 /**
249 * @throws IndexOutOfBoundsException {@inheritDoc}
250 * @see #length()
251 */
252 @Override
253 public synchronized void setCharAt(int index, char ch) {
254 if ((index < 0) || (index >= count))
255 throw new StringIndexOutOfBoundsException(index);
256 toStringCache = null;
257 value[index] = ch;
258 }
259
260 @Override
261 public synchronized StringBuffer append(Object obj) {
262 toStringCache = null;
263 super.append(String.valueOf(obj));
264 return this;
265 }
266
267 @Override
268 public synchronized StringBuffer append(String str) {
269 toStringCache = null;
270 super.append(str);
271 return this;
272 }
273
274 /**
275 * Appends the specified {@code StringBuffer} to this sequence.
276 * <p>
277 * The characters of the {@code StringBuffer} argument are appended,
278 * in order, to the contents of this {@code StringBuffer}, increasing the
279 * length of this {@code StringBuffer} by the length of the argument.
280 * If {@code sb} is {@code null}, then the four characters
281 * {@code "null"} are appended to this {@code StringBuffer}.
282 * <p>
283 * Let <i>n</i> be the length of the old character sequence, the one
284 * contained in the {@code StringBuffer} just prior to execution of the
285 * {@code append} method. Then the character at index <i>k</i> in
286 * the new character sequence is equal to the character at index <i>k</i>
287 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
288 * otherwise, it is equal to the character at index <i>k-n</i> in the
289 * argument {@code sb}.
290 * <p>
291 * This method synchronizes on {@code this}, the destination
292 * object, but does not synchronize on the source ({@code sb}).
293 *
294 * @param sb the {@code StringBuffer} to append.
295 * @return a reference to this object.
296 * @since 1.4
297 */
298 public synchronized StringBuffer append(StringBuffer sb) {
299 toStringCache = null;
300 super.append(sb);
301 return this;
302 }
303
304 /**
305 * @since 1.8
306 */
307 @Override
308 synchronized StringBuffer append(AbstractStringBuilder asb) {
309 toStringCache = null;
310 super.append(asb);
311 return this;
312 }
313
314 /**
315 * Appends the specified {@code CharSequence} to this
316 * sequence.
317 * <p>
318 * The characters of the {@code CharSequence} argument are appended,
319 * in order, increasing the length of this sequence by the length of the
320 * argument.
321 *
322 * <p>The result of this method is exactly the same as if it were an
323 * invocation of this.append(s, 0, s.length());
324 *
325 * <p>This method synchronizes on {@code this}, the destination
326 * object, but does not synchronize on the source ({@code s}).
327 *
328 * <p>If {@code s} is {@code null}, then the four characters
329 * {@code "null"} are appended.
330 *
331 * @param s the {@code CharSequence} to append.
332 * @return a reference to this object.
333 * @since 1.5
334 */
335 @Override
336 public synchronized StringBuffer append(CharSequence s) {
337 toStringCache = null;
338 super.append(s);
339 return this;
340 }
341
342 /**
343 * @throws IndexOutOfBoundsException {@inheritDoc}
344 * @since 1.5
345 */
346 @Override
347 public synchronized StringBuffer append(CharSequence s, int start, int end)
348 {
349 toStringCache = null;
350 super.append(s, start, end);
351 return this;
352 }
353
354 @Override
355 public synchronized StringBuffer append(char[] str) {
356 toStringCache = null;
357 super.append(str);
358 return this;
359 }
360
361 /**
362 * @throws IndexOutOfBoundsException {@inheritDoc}
363 */
364 @Override
365 public synchronized StringBuffer append(char[] str, int offset, int len) {
366 toStringCache = null;
367 super.append(str, offset, len);
368 return this;
369 }
370
371 @Override
372 public synchronized StringBuffer append(boolean b) {
373 toStringCache = null;
374 super.append(b);
375 return this;
376 }
377
378 @Override
379 public synchronized StringBuffer append(char c) {
380 toStringCache = null;
381 super.append(c);
382 return this;
383 }
384
385 @Override
386 public synchronized StringBuffer append(int i) {
387 toStringCache = null;
388 super.append(i);
389 return this;
390 }
391
392 /**
393 * @since 1.5
394 */
395 @Override
396 public synchronized StringBuffer appendCodePoint(int codePoint) {
397 toStringCache = null;
398 super.appendCodePoint(codePoint);
399 return this;
400 }
401
402 @Override
403 public synchronized StringBuffer append(long lng) {
404 toStringCache = null;
405 super.append(lng);
406 return this;
407 }
408
409 @Override
410 public synchronized StringBuffer append(float f) {
411 toStringCache = null;
412 super.append(f);
413 return this;
414 }
415
416 @Override
417 public synchronized StringBuffer append(double d) {
418 toStringCache = null;
419 super.append(d);
420 return this;
421 }
422
423 /**
424 * @throws StringIndexOutOfBoundsException {@inheritDoc}
425 * @since 1.2
426 */
427 @Override
428 public synchronized StringBuffer delete(int start, int end) {
429 toStringCache = null;
430 super.delete(start, end);
431 return this;
432 }
433
434 /**
435 * @throws StringIndexOutOfBoundsException {@inheritDoc}
436 * @since 1.2
437 */
438 @Override
439 public synchronized StringBuffer deleteCharAt(int index) {
440 toStringCache = null;
441 super.deleteCharAt(index);
442 return this;
443 }
444
445 /**
446 * @throws StringIndexOutOfBoundsException {@inheritDoc}
447 * @since 1.2
448 */
449 @Override
450 public synchronized StringBuffer replace(int start, int end, String str) {
451 toStringCache = null;
452 super.replace(start, end, str);
453 return this;
454 }
455
456 /**
457 * @throws StringIndexOutOfBoundsException {@inheritDoc}
458 * @since 1.2
459 */
460 @Override
461 public synchronized String substring(int start) {
462 return substring(start, count);
463 }
464
465 /**
466 * @throws IndexOutOfBoundsException {@inheritDoc}
467 * @since 1.4
468 */
469 @Override
470 public synchronized CharSequence subSequence(int start, int end) {
471 return super.substring(start, end);
472 }
473
474 /**
475 * @throws StringIndexOutOfBoundsException {@inheritDoc}
476 * @since 1.2
477 */
478 @Override
479 public synchronized String substring(int start, int end) {
480 return super.substring(start, end);
481 }
482
483 /**
484 * @throws StringIndexOutOfBoundsException {@inheritDoc}
485 * @since 1.2
486 */
487 @Override
488 public synchronized StringBuffer insert(int index, char[] str, int offset,
489 int len)
490 {
491 toStringCache = null;
492 super.insert(index, str, offset, len);
493 return this;
494 }
495
496 /**
497 * @throws StringIndexOutOfBoundsException {@inheritDoc}
498 */
499 @Override
500 public synchronized StringBuffer insert(int offset, Object obj) {
501 toStringCache = null;
502 super.insert(offset, String.valueOf(obj));
503 return this;
504 }
505
506 /**
507 * @throws StringIndexOutOfBoundsException {@inheritDoc}
508 */
509 @Override
510 public synchronized StringBuffer insert(int offset, String str) {
511 toStringCache = null;
512 super.insert(offset, str);
513 return this;
514 }
515
516 /**
517 * @throws StringIndexOutOfBoundsException {@inheritDoc}
518 */
519 @Override
520 public synchronized StringBuffer insert(int offset, char[] str) {
521 toStringCache = null;
522 super.insert(offset, str);
523 return this;
524 }
525
526 /**
527 * @throws IndexOutOfBoundsException {@inheritDoc}
528 * @since 1.5
529 */
530 @Override
531 public StringBuffer insert(int dstOffset, CharSequence s) {
532 // Note, synchronization achieved via invocations of other StringBuffer methods
533 // after narrowing of s to specific type
534 // Ditto for toStringCache clearing
535 super.insert(dstOffset, s);
536 return this;
537 }
538
539 /**
540 * @throws IndexOutOfBoundsException {@inheritDoc}
541 * @since 1.5
542 */
543 @Override
544 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
545 int start, int end)
546 {
547 toStringCache = null;
548 super.insert(dstOffset, s, start, end);
549 return this;
550 }
551
552 /**
553 * @throws StringIndexOutOfBoundsException {@inheritDoc}
554 */
555 @Override
556 public StringBuffer insert(int offset, boolean b) {
557 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
558 // after conversion of b to String by super class method
559 // Ditto for toStringCache clearing
560 super.insert(offset, b);
561 return this;
562 }
563
564 /**
565 * @throws IndexOutOfBoundsException {@inheritDoc}
566 */
567 @Override
568 public synchronized StringBuffer insert(int offset, char c) {
569 toStringCache = null;
570 super.insert(offset, c);
571 return this;
572 }
573
574 /**
575 * @throws StringIndexOutOfBoundsException {@inheritDoc}
576 */
577 @Override
578 public StringBuffer insert(int offset, int i) {
579 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
580 // after conversion of i to String by super class method
581 // Ditto for toStringCache clearing
582 super.insert(offset, i);
583 return this;
584 }
585
586 /**
587 * @throws StringIndexOutOfBoundsException {@inheritDoc}
588 */
589 @Override
590 public StringBuffer insert(int offset, long l) {
591 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
592 // after conversion of l to String by super class method
593 // Ditto for toStringCache clearing
594 super.insert(offset, l);
595 return this;
596 }
597
598 /**
599 * @throws StringIndexOutOfBoundsException {@inheritDoc}
600 */
601 @Override
602 public StringBuffer insert(int offset, float f) {
603 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
604 // after conversion of f to String by super class method
605 // Ditto for toStringCache clearing
606 super.insert(offset, f);
607 return this;
608 }
609
610 /**
611 * @throws StringIndexOutOfBoundsException {@inheritDoc}
612 */
613 @Override
614 public StringBuffer insert(int offset, double d) {
615 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
616 // after conversion of d to String by super class method
617 // Ditto for toStringCache clearing
618 super.insert(offset, d);
619 return this;
620 }
621
622 /**
623 * @since 1.4
624 */
625 @Override
626 public int indexOf(String str) {
627 // Note, synchronization achieved via invocations of other StringBuffer methods
628 return super.indexOf(str);
629 }
630
631 /**
632 * @since 1.4
633 */
634 @Override
635 public synchronized int indexOf(String str, int fromIndex) {
636 return super.indexOf(str, fromIndex);
637 }
638
639 /**
640 * @since 1.4
641 */
642 @Override
643 public int lastIndexOf(String str) {
644 // Note, synchronization achieved via invocations of other StringBuffer methods
645 return lastIndexOf(str, count);
646 }
647
648 /**
649 * @since 1.4
650 */
651 @Override
652 public synchronized int lastIndexOf(String str, int fromIndex) {
653 return super.lastIndexOf(str, fromIndex);
654 }
655
656 /**
657 * @since JDK1.0.2
658 */
659 @Override
660 public synchronized StringBuffer reverse() {
661 toStringCache = null;
662 super.reverse();
663 return this;
664 }
665
666 @Override
667 public synchronized String toString() {
668 if (toStringCache == null) {
669 toStringCache = Arrays.copyOfRange(value, 0, count);
670 }
671 return new String(toStringCache, true);
672 }
673
674 /**
675 * Serializable fields for StringBuffer.
676 *
677 * @serialField value char[]
678 * The backing character array of this StringBuffer.
679 * @serialField count int
680 * The number of characters in this StringBuffer.
681 * @serialField shared boolean
682 * A flag indicating whether the backing array is shared.
683 * The value is ignored upon deserialization.
684 */
685 private static final java.io.ObjectStreamField[] serialPersistentFields =
686 {
687 new java.io.ObjectStreamField("value", char[].class),
688 new java.io.ObjectStreamField("count", Integer.TYPE),
689 new java.io.ObjectStreamField("shared", Boolean.TYPE),
690 };
691
692 /**
693 * readObject is called to restore the state of the StringBuffer from
694 * a stream.
695 */
696 private synchronized void writeObject(java.io.ObjectOutputStream s)
697 throws java.io.IOException {
698 java.io.ObjectOutputStream.PutField fields = s.putFields();
699 fields.put("value", value);
700 fields.put("count", count);
701 fields.put("shared", false);
702 s.writeFields();
703 }
704
705 /**
706 * readObject is called to restore the state of the StringBuffer from
707 * a stream.
708 */
709 private void readObject(java.io.ObjectInputStream s)
710 throws java.io.IOException, ClassNotFoundException {
711 java.io.ObjectInputStream.GetField fields = s.readFields();
712 value = (char[])fields.get("value", null);
713 count = fields.get("count", 0);
714 }
715 }