1 /*
2 * Copyright (c) 1994, 2012, 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 /** use serialVersionUID from JDK 1.0.2 for interoperability */
102 static final long serialVersionUID = 3388685877147921107L;
103
104 /**
105 * Constructs a string buffer with no characters in it and an
106 * initial capacity of 16 characters.
107 */
108 public StringBuffer() {
109 super(16);
110 }
111
112 /**
113 * Constructs a string buffer with no characters in it and
114 * the specified initial capacity.
115 *
116 * @param capacity the initial capacity.
117 * @exception NegativeArraySizeException if the {@code capacity}
118 * argument is less than {@code 0}.
119 */
120 public StringBuffer(int capacity) {
121 super(capacity);
122 }
123
124 /**
125 * Constructs a string buffer initialized to the contents of the
126 * specified string. The initial capacity of the string buffer is
127 * {@code 16} plus the length of the string argument.
128 *
129 * @param str the initial contents of the buffer.
130 */
131 public StringBuffer(String str) {
132 super(str.length() + 16);
133 append(str);
134 }
135
136 /**
137 * Constructs a string buffer that contains the same characters
138 * as the specified {@code CharSequence}. The initial capacity of
139 * the string buffer is {@code 16} plus the length of the
140 * {@code CharSequence} argument.
141 * <p>
142 * If the length of the specified {@code CharSequence} is
143 * less than or equal to zero, then an empty buffer of capacity
144 * {@code 16} is returned.
145 *
146 * @param seq the sequence to copy.
147 * @since 1.5
148 */
149 public StringBuffer(CharSequence seq) {
150 this(seq.length() + 16);
151 append(seq);
152 }
153
154 @Override
155 public synchronized int length() {
156 return count;
157 }
158
159 @Override
160 public synchronized int capacity() {
161 return value.length;
162 }
163
164
165 @Override
166 public synchronized void ensureCapacity(int minimumCapacity) {
167 if (minimumCapacity > value.length) {
168 expandCapacity(minimumCapacity);
169 }
170 }
171
172 /**
173 * @since 1.5
174 */
175 @Override
176 public synchronized void trimToSize() {
177 super.trimToSize();
178 }
179
180 /**
181 * @throws IndexOutOfBoundsException {@inheritDoc}
182 * @see #length()
183 */
184 @Override
185 public synchronized void setLength(int newLength) {
186 super.setLength(newLength);
187 }
188
189 /**
190 * @throws IndexOutOfBoundsException {@inheritDoc}
191 * @see #length()
192 */
193 @Override
194 public synchronized char charAt(int index) {
195 if ((index < 0) || (index >= count))
196 throw new StringIndexOutOfBoundsException(index);
197 return value[index];
198 }
199
200 /**
201 * @since 1.5
202 */
203 @Override
204 public synchronized int codePointAt(int index) {
205 return super.codePointAt(index);
206 }
207
208 /**
209 * @since 1.5
210 */
211 @Override
212 public synchronized int codePointBefore(int index) {
213 return super.codePointBefore(index);
214 }
215
216 /**
217 * @since 1.5
218 */
219 @Override
220 public synchronized int codePointCount(int beginIndex, int endIndex) {
221 return super.codePointCount(beginIndex, endIndex);
222 }
223
224 /**
225 * @since 1.5
226 */
227 @Override
228 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
229 return super.offsetByCodePoints(index, codePointOffset);
230 }
231
232 /**
233 * @throws IndexOutOfBoundsException {@inheritDoc}
234 */
235 @Override
236 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
237 int dstBegin)
238 {
239 super.getChars(srcBegin, srcEnd, dst, dstBegin);
240 }
241
242 /**
243 * @throws IndexOutOfBoundsException {@inheritDoc}
244 * @see #length()
245 */
246 @Override
247 public synchronized void setCharAt(int index, char ch) {
248 if ((index < 0) || (index >= count))
249 throw new StringIndexOutOfBoundsException(index);
250 value[index] = ch;
251 }
252
253 @Override
254 public synchronized StringBuffer append(Object obj) {
255 super.append(String.valueOf(obj));
256 return this;
257 }
258
259 @Override
260 public synchronized StringBuffer append(String str) {
261 super.append(str);
262 return this;
263 }
264
265 /**
266 * Appends the specified {@code StringBuffer} to this sequence.
267 * <p>
268 * The characters of the {@code StringBuffer} argument are appended,
269 * in order, to the contents of this {@code StringBuffer}, increasing the
270 * length of this {@code StringBuffer} by the length of the argument.
271 * If {@code sb} is {@code null}, then the four characters
272 * {@code "null"} are appended to this {@code StringBuffer}.
273 * <p>
274 * Let <i>n</i> be the length of the old character sequence, the one
275 * contained in the {@code StringBuffer} just prior to execution of the
276 * {@code append} method. Then the character at index <i>k</i> in
277 * the new character sequence is equal to the character at index <i>k</i>
278 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
279 * otherwise, it is equal to the character at index <i>k-n</i> in the
280 * argument {@code sb}.
281 * <p>
282 * This method synchronizes on {@code this}, the destination
283 * object, but does not synchronize on the source ({@code sb}).
284 *
285 * @param sb the {@code StringBuffer} to append.
286 * @return a reference to this object.
287 * @since 1.4
288 */
289 public synchronized StringBuffer append(StringBuffer sb) {
290 super.append(sb);
291 return this;
292 }
293
294 /**
295 * @since 1.8
296 */
297 @Override
298 synchronized StringBuffer append(AbstractStringBuilder asb) {
299 super.append(asb);
300 return this;
301 }
302
303 /**
304 * Appends the specified {@code CharSequence} to this
305 * sequence.
306 * <p>
307 * The characters of the {@code CharSequence} argument are appended,
308 * in order, increasing the length of this sequence by the length of the
309 * argument.
310 *
311 * <p>The result of this method is exactly the same as if it were an
312 * invocation of this.append(s, 0, s.length());
313 *
314 * <p>This method synchronizes on {@code this}, the destination
315 * object, but does not synchronize on the source ({@code s}).
316 *
317 * <p>If {@code s} is {@code null}, then the four characters
318 * {@code "null"} are appended.
319 *
320 * @param s the {@code CharSequence} to append.
321 * @return a reference to this object.
322 * @since 1.5
323 */
324 @Override
325 public StringBuffer append(CharSequence s) {
326 // Note, synchronization achieved via invocations of other StringBuffer methods after
327 // narrowing of s to specific type
328 super.append(s);
329 return this;
330 }
331
332 /**
333 * @throws IndexOutOfBoundsException {@inheritDoc}
334 * @since 1.5
335 */
336 @Override
337 public synchronized StringBuffer append(CharSequence s, int start, int end)
338 {
339 super.append(s, start, end);
340 return this;
341 }
342
343 @Override
344 public synchronized StringBuffer append(char[] str) {
345 super.append(str);
346 return this;
347 }
348
349 /**
350 * @throws IndexOutOfBoundsException {@inheritDoc}
351 */
352 @Override
353 public synchronized StringBuffer append(char[] str, int offset, int len) {
354 super.append(str, offset, len);
355 return this;
356 }
357
358 @Override
359 public synchronized StringBuffer append(boolean b) {
360 super.append(b);
361 return this;
362 }
363
364 @Override
365 public synchronized StringBuffer append(char c) {
366 super.append(c);
367 return this;
368 }
369
370 @Override
371 public synchronized StringBuffer append(int i) {
372 super.append(i);
373 return this;
374 }
375
376 /**
377 * @since 1.5
378 */
379 @Override
380 public synchronized StringBuffer appendCodePoint(int codePoint) {
381 super.appendCodePoint(codePoint);
382 return this;
383 }
384
385 @Override
386 public synchronized StringBuffer append(long lng) {
387 super.append(lng);
388 return this;
389 }
390
391 @Override
392 public synchronized StringBuffer append(float f) {
393 super.append(f);
394 return this;
395 }
396
397 @Override
398 public synchronized StringBuffer append(double d) {
399 super.append(d);
400 return this;
401 }
402
403 /**
404 * @throws StringIndexOutOfBoundsException {@inheritDoc}
405 * @since 1.2
406 */
407 @Override
408 public synchronized StringBuffer delete(int start, int end) {
409 super.delete(start, end);
410 return this;
411 }
412
413 /**
414 * @throws StringIndexOutOfBoundsException {@inheritDoc}
415 * @since 1.2
416 */
417 @Override
418 public synchronized StringBuffer deleteCharAt(int index) {
419 super.deleteCharAt(index);
420 return this;
421 }
422
423 /**
424 * @throws StringIndexOutOfBoundsException {@inheritDoc}
425 * @since 1.2
426 */
427 @Override
428 public synchronized StringBuffer replace(int start, int end, String str) {
429 super.replace(start, end, str);
430 return this;
431 }
432
433 /**
434 * @throws StringIndexOutOfBoundsException {@inheritDoc}
435 * @since 1.2
436 */
437 @Override
438 public synchronized String substring(int start) {
439 return substring(start, count);
440 }
441
442 /**
443 * @throws IndexOutOfBoundsException {@inheritDoc}
444 * @since 1.4
445 */
446 @Override
447 public synchronized CharSequence subSequence(int start, int end) {
448 return super.substring(start, end);
449 }
450
451 /**
452 * @throws StringIndexOutOfBoundsException {@inheritDoc}
453 * @since 1.2
454 */
455 @Override
456 public synchronized String substring(int start, int end) {
457 return super.substring(start, end);
458 }
459
460 /**
461 * @throws StringIndexOutOfBoundsException {@inheritDoc}
462 * @since 1.2
463 */
464 @Override
465 public synchronized StringBuffer insert(int index, char[] str, int offset,
466 int len)
467 {
468 super.insert(index, str, offset, len);
469 return this;
470 }
471
472 /**
473 * @throws StringIndexOutOfBoundsException {@inheritDoc}
474 */
475 @Override
476 public synchronized StringBuffer insert(int offset, Object obj) {
477 super.insert(offset, String.valueOf(obj));
478 return this;
479 }
480
481 /**
482 * @throws StringIndexOutOfBoundsException {@inheritDoc}
483 */
484 @Override
485 public synchronized StringBuffer insert(int offset, String str) {
486 super.insert(offset, str);
487 return this;
488 }
489
490 /**
491 * @throws StringIndexOutOfBoundsException {@inheritDoc}
492 */
493 @Override
494 public synchronized StringBuffer insert(int offset, char[] str) {
495 super.insert(offset, str);
496 return this;
497 }
498
499 /**
500 * @throws IndexOutOfBoundsException {@inheritDoc}
501 * @since 1.5
502 */
503 @Override
504 public StringBuffer insert(int dstOffset, CharSequence s) {
505 // Note, synchronization achieved via invocations of other StringBuffer methods
506 // after narrowing of s to specific type
507 super.insert(dstOffset, s);
508 return this;
509 }
510
511 /**
512 * @throws IndexOutOfBoundsException {@inheritDoc}
513 * @since 1.5
514 */
515 @Override
516 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
517 int start, int end)
518 {
519 super.insert(dstOffset, s, start, end);
520 return this;
521 }
522
523 /**
524 * @throws StringIndexOutOfBoundsException {@inheritDoc}
525 */
526 @Override
527 public StringBuffer insert(int offset, boolean b) {
528 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
529 // after conversion of b to String by super class method
530 super.insert(offset, b);
531 return this;
532 }
533
534 /**
535 * @throws IndexOutOfBoundsException {@inheritDoc}
536 */
537 @Override
538 public synchronized StringBuffer insert(int offset, char c) {
539 super.insert(offset, c);
540 return this;
541 }
542
543 /**
544 * @throws StringIndexOutOfBoundsException {@inheritDoc}
545 */
546 @Override
547 public StringBuffer insert(int offset, int i) {
548 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
549 // after conversion of i to String by super class method
550 super.insert(offset, i);
551 return this;
552 }
553
554 /**
555 * @throws StringIndexOutOfBoundsException {@inheritDoc}
556 */
557 @Override
558 public StringBuffer insert(int offset, long l) {
559 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
560 // after conversion of l to String by super class method
561 super.insert(offset, l);
562 return this;
563 }
564
565 /**
566 * @throws StringIndexOutOfBoundsException {@inheritDoc}
567 */
568 @Override
569 public StringBuffer insert(int offset, float f) {
570 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
571 // after conversion of f to String by super class method
572 super.insert(offset, f);
573 return this;
574 }
575
576 /**
577 * @throws StringIndexOutOfBoundsException {@inheritDoc}
578 */
579 @Override
580 public StringBuffer insert(int offset, double d) {
581 // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
582 // after conversion of d to String by super class method
583 super.insert(offset, d);
584 return this;
585 }
586
587 /**
588 * @since 1.4
589 */
590 @Override
591 public int indexOf(String str) {
592 // Note, synchronization achieved via invocations of other StringBuffer methods
593 return super.indexOf(str);
594 }
595
596 /**
597 * @since 1.4
598 */
599 @Override
600 public synchronized int indexOf(String str, int fromIndex) {
601 return super.indexOf(str, fromIndex);
602 }
603
604 /**
605 * @since 1.4
606 */
607 @Override
608 public int lastIndexOf(String str) {
609 // Note, synchronization achieved via invocations of other StringBuffer methods
610 return lastIndexOf(str, count);
611 }
612
613 /**
614 * @since 1.4
615 */
616 @Override
617 public synchronized int lastIndexOf(String str, int fromIndex) {
618 return super.lastIndexOf(str, fromIndex);
619 }
620
621 /**
622 * @since JDK1.0.2
623 */
624 @Override
625 public synchronized StringBuffer reverse() {
626 super.reverse();
627 return this;
628 }
629
630 @Override
631 public synchronized String toString() {
632 return new String(value, 0, count);
633 }
634
635 /**
636 * Serializable fields for StringBuffer.
637 *
638 * @serialField value char[]
639 * The backing character array of this StringBuffer.
640 * @serialField count int
641 * The number of characters in this StringBuffer.
642 * @serialField shared boolean
643 * A flag indicating whether the backing array is shared.
644 * The value is ignored upon deserialization.
645 */
646 private static final java.io.ObjectStreamField[] serialPersistentFields =
647 {
648 new java.io.ObjectStreamField("value", char[].class),
649 new java.io.ObjectStreamField("count", Integer.TYPE),
650 new java.io.ObjectStreamField("shared", Boolean.TYPE),
651 };
652
653 /**
654 * readObject is called to restore the state of the StringBuffer from
655 * a stream.
656 */
657 private synchronized void writeObject(java.io.ObjectOutputStream s)
658 throws java.io.IOException {
659 java.io.ObjectOutputStream.PutField fields = s.putFields();
660 fields.put("value", value);
661 fields.put("count", count);
662 fields.put("shared", false);
663 s.writeFields();
664 }
665
666 /**
667 * readObject is called to restore the state of the StringBuffer from
668 * a stream.
669 */
670 private void readObject(java.io.ObjectInputStream s)
671 throws java.io.IOException, ClassNotFoundException {
672 java.io.ObjectInputStream.GetField fields = s.readFields();
673 value = (char[])fields.get("value", null);
674 count = fields.get("count", 0);
675 }
676 }