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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 }