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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
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.
42 * The principal operations on a <code>StringBuffer</code> are the
43 * <code>append</code> and <code>insert</code> 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</code> method always adds these characters at the end
48 * of the buffer; the <code>insert</code> method adds the characters at
51 * For example, if <code>z</code> refers to a string buffer object
52 * whose current contents are "<code>start</code>", then
53 * the method call <code>z.append("le")</code> would cause the string
54 * buffer to contain "<code>startle</code>", whereas
55 * <code>z.insert(4, "le")</code> would alter the string buffer to
56 * contain "<code>starlet</code>".
58 * In general, if sb refers to an instance of a <code>StringBuffer</code>,
59 * then <code>sb.append(x)</code> has the same effect as
60 * <code>sb.insert(sb.length(), x)</code>.
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.
66 * Every string buffer has a capacity. As long as the length of the
67 * character sequence contained in the string buffer does not exceed
68 * the capacity, it is not necessary to allocate a new internal
69 * buffer array. If the internal buffer overflows, it is
70 * automatically made larger.
72 * As of release JDK 5, this class has been supplemented with an equivalent
73 * class designed for use by a single thread, {@link StringBuilder}. The
74 * <tt>StringBuilder</tt> class should generally be used in preference to
75 * this one, as it supports all of the same operations but it is faster, as
76 * it performs no synchronization.
78 * @author Arthur van Hoff
79 * @see java.lang.StringBuilder
80 * @see java.lang.String
83 public final class StringBuffer
84 extends AbstractStringBuilder
85 implements java.io.Serializable, CharSequence
88 /** use serialVersionUID from JDK 1.0.2 for interoperability */
89 static final long serialVersionUID = 3388685877147921107L;
92 * Constructs a string buffer with no characters in it and an
93 * initial capacity of 16 characters.
95 public StringBuffer() {
100 * Constructs a string buffer with no characters in it and
101 * the specified initial capacity.
103 * @param capacity the initial capacity.
104 * @exception NegativeArraySizeException if the <code>capacity</code>
105 * argument is less than <code>0</code>.
107 public StringBuffer(int capacity) {
112 * Constructs a string buffer initialized to the contents of the
113 * specified string. The initial capacity of the string buffer is
114 * <code>16</code> plus the length of the string argument.
116 * @param str the initial contents of the buffer.
117 * @exception NullPointerException if <code>str</code> is <code>null</code>
119 public StringBuffer(String str) {
120 super(str.length() + 16);
125 * Constructs a string buffer that contains the same characters
126 * as the specified <code>CharSequence</code>. The initial capacity of
127 * the string buffer is <code>16</code> plus the length of the
128 * <code>CharSequence</code> argument.
130 * If the length of the specified <code>CharSequence</code> is
131 * less than or equal to zero, then an empty buffer of capacity
132 * <code>16</code> is returned.
134 * @param seq the sequence to copy.
135 * @exception NullPointerException if <code>seq</code> is <code>null</code>
138 public StringBuffer(CharSequence seq) {
139 this(seq.length() + 16);
143 public synchronized int length() {
147 public synchronized int capacity() {
152 public synchronized void ensureCapacity(int minimumCapacity) {
153 if (minimumCapacity > value.length) {
154 expandCapacity(minimumCapacity);
161 public synchronized void trimToSize() {
166 * @throws IndexOutOfBoundsException {@inheritDoc}
169 public synchronized void setLength(int newLength) {
170 super.setLength(newLength);
174 * @throws IndexOutOfBoundsException {@inheritDoc}
177 public synchronized char charAt(int index) {
178 if ((index < 0) || (index >= count))
179 throw new StringIndexOutOfBoundsException(index);
186 public synchronized int codePointAt(int index) {
187 return super.codePointAt(index);
193 public synchronized int codePointBefore(int index) {
194 return super.codePointBefore(index);
200 public synchronized int codePointCount(int beginIndex, int endIndex) {
201 return super.codePointCount(beginIndex, endIndex);
207 public synchronized int offsetByCodePoints(int index, int codePointOffset) {
208 return super.offsetByCodePoints(index, codePointOffset);
212 * @throws NullPointerException {@inheritDoc}
213 * @throws IndexOutOfBoundsException {@inheritDoc}
215 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
218 super.getChars(srcBegin, srcEnd, dst, dstBegin);
222 * @throws IndexOutOfBoundsException {@inheritDoc}
225 public synchronized void setCharAt(int index, char ch) {
226 if ((index < 0) || (index >= count))
227 throw new StringIndexOutOfBoundsException(index);
231 public synchronized StringBuffer append(Object obj) {
232 super.append(String.valueOf(obj));
236 public synchronized StringBuffer append(String str) {
242 * Appends the specified <tt>StringBuffer</tt> to this sequence.
244 * The characters of the <tt>StringBuffer</tt> argument are appended,
245 * in order, to the contents of this <tt>StringBuffer</tt>, increasing the
246 * length of this <tt>StringBuffer</tt> by the length of the argument.
247 * If <tt>sb</tt> is <tt>null</tt>, then the four characters
248 * <tt>"null"</tt> are appended to this <tt>StringBuffer</tt>.
250 * Let <i>n</i> be the length of the old character sequence, the one
251 * contained in the <tt>StringBuffer</tt> just prior to execution of the
252 * <tt>append</tt> method. Then the character at index <i>k</i> in
253 * the new character sequence is equal to the character at index <i>k</i>
254 * in the old character sequence, if <i>k</i> is less than <i>n</i>;
255 * otherwise, it is equal to the character at index <i>k-n</i> in the
256 * argument <code>sb</code>.
258 * This method synchronizes on <code>this</code> (the destination)
259 * object but does not synchronize on the source (<code>sb</code>).
261 * @param sb the <tt>StringBuffer</tt> to append.
262 * @return a reference to this object.
265 public synchronized StringBuffer append(StringBuffer sb) {
272 * Appends the specified <code>CharSequence</code> to this
275 * The characters of the <code>CharSequence</code> argument are appended,
276 * in order, increasing the length of this sequence by the length of the
279 * <p>The result of this method is exactly the same as if it were an
280 * invocation of this.append(s, 0, s.length());
282 * <p>This method synchronizes on this (the destination)
283 * object but does not synchronize on the source (<code>s</code>).
285 * <p>If <code>s</code> is <code>null</code>, then the four characters
286 * <code>"null"</code> are appended.
288 * @param s the <code>CharSequence</code> to append.
289 * @return a reference to this object.
292 public StringBuffer append(CharSequence s) {
293 // Note, synchronization achieved via other invocations
296 if (s instanceof String)
297 return this.append((String)s);
298 if (s instanceof StringBuffer)
299 return this.append((StringBuffer)s);
300 return this.append(s, 0, s.length());
304 * @throws IndexOutOfBoundsException {@inheritDoc}
307 public synchronized StringBuffer append(CharSequence s, int start, int end)
309 super.append(s, start, end);
313 public synchronized StringBuffer append(char[] str) {
319 * @throws IndexOutOfBoundsException {@inheritDoc}
321 public synchronized StringBuffer append(char[] str, int offset, int len) {
322 super.append(str, offset, len);
326 public synchronized StringBuffer append(boolean b) {
331 public synchronized StringBuffer append(char c) {
336 public synchronized StringBuffer append(int i) {
344 public synchronized StringBuffer appendCodePoint(int codePoint) {
345 super.appendCodePoint(codePoint);
349 public synchronized StringBuffer append(long lng) {
354 public synchronized StringBuffer append(float f) {
359 public synchronized StringBuffer append(double d) {
365 * @throws StringIndexOutOfBoundsException {@inheritDoc}
368 public synchronized StringBuffer delete(int start, int end) {
369 super.delete(start, end);
374 * @throws StringIndexOutOfBoundsException {@inheritDoc}
377 public synchronized StringBuffer deleteCharAt(int index) {
378 super.deleteCharAt(index);
383 * @throws StringIndexOutOfBoundsException {@inheritDoc}
386 public synchronized StringBuffer replace(int start, int end, String str) {
387 super.replace(start, end, str);
392 * @throws StringIndexOutOfBoundsException {@inheritDoc}
395 public synchronized String substring(int start) {
396 return substring(start, count);
400 * @throws IndexOutOfBoundsException {@inheritDoc}
403 public synchronized CharSequence subSequence(int start, int end) {
404 return super.substring(start, end);
408 * @throws StringIndexOutOfBoundsException {@inheritDoc}
411 public synchronized String substring(int start, int end) {
412 return super.substring(start, end);
416 * @throws StringIndexOutOfBoundsException {@inheritDoc}
419 public synchronized StringBuffer insert(int index, char[] str, int offset,
422 super.insert(index, str, offset, len);
427 * @throws StringIndexOutOfBoundsException {@inheritDoc}
429 public synchronized StringBuffer insert(int offset, Object obj) {
430 super.insert(offset, String.valueOf(obj));
435 * @throws StringIndexOutOfBoundsException {@inheritDoc}
437 public synchronized StringBuffer insert(int offset, String str) {
438 super.insert(offset, str);
443 * @throws StringIndexOutOfBoundsException {@inheritDoc}
445 public synchronized StringBuffer insert(int offset, char[] str) {
446 super.insert(offset, str);
451 * @throws IndexOutOfBoundsException {@inheritDoc}
454 public StringBuffer insert(int dstOffset, CharSequence s) {
455 // Note, synchronization achieved via other invocations
458 if (s instanceof String)
459 return this.insert(dstOffset, (String)s);
460 return this.insert(dstOffset, s, 0, s.length());
464 * @throws IndexOutOfBoundsException {@inheritDoc}
467 public synchronized StringBuffer insert(int dstOffset, CharSequence s,
470 super.insert(dstOffset, s, start, end);
475 * @throws StringIndexOutOfBoundsException {@inheritDoc}
477 public StringBuffer insert(int offset, boolean b) {
478 return insert(offset, String.valueOf(b));
482 * @throws IndexOutOfBoundsException {@inheritDoc}
484 public synchronized StringBuffer insert(int offset, char c) {
485 super.insert(offset, c);
490 * @throws StringIndexOutOfBoundsException {@inheritDoc}
492 public StringBuffer insert(int offset, int i) {
493 return insert(offset, String.valueOf(i));
497 * @throws StringIndexOutOfBoundsException {@inheritDoc}
499 public StringBuffer insert(int offset, long l) {
500 return insert(offset, String.valueOf(l));
504 * @throws StringIndexOutOfBoundsException {@inheritDoc}
506 public StringBuffer insert(int offset, float f) {
507 return insert(offset, String.valueOf(f));
511 * @throws StringIndexOutOfBoundsException {@inheritDoc}
513 public StringBuffer insert(int offset, double d) {
514 return insert(offset, String.valueOf(d));
518 * @throws NullPointerException {@inheritDoc}
521 public int indexOf(String str) {
522 return indexOf(str, 0);
526 * @throws NullPointerException {@inheritDoc}
529 public synchronized int indexOf(String str, int fromIndex) {
530 return String.indexOf(value, 0, count,
531 str.toCharArray(), 0, str.length(), fromIndex);
535 * @throws NullPointerException {@inheritDoc}
538 public int lastIndexOf(String str) {
539 // Note, synchronization achieved via other invocations
540 return lastIndexOf(str, count);
544 * @throws NullPointerException {@inheritDoc}
547 public synchronized int lastIndexOf(String str, int fromIndex) {
548 return String.lastIndexOf(value, 0, count,
549 str.toCharArray(), 0, str.length(), fromIndex);
555 public synchronized StringBuffer reverse() {
560 public synchronized String toString() {
561 return new String(value, 0, count);
565 * Serializable fields for StringBuffer.
567 * @serialField value char[]
568 * The backing character array of this StringBuffer.
569 * @serialField count int
570 * The number of characters in this StringBuffer.
571 * @serialField shared boolean
572 * A flag indicating whether the backing array is shared.
573 * The value is ignored upon deserialization.
575 private static final java.io.ObjectStreamField[] serialPersistentFields =
577 new java.io.ObjectStreamField("value", char[].class),
578 new java.io.ObjectStreamField("count", Integer.TYPE),
579 new java.io.ObjectStreamField("shared", Boolean.TYPE),
583 * readObject is called to restore the state of the StringBuffer from
586 private synchronized void writeObject(java.io.ObjectOutputStream s)
587 throws java.io.IOException {
588 java.io.ObjectOutputStream.PutField fields = s.putFields();
589 fields.put("value", value);
590 fields.put("count", count);
591 fields.put("shared", false);
596 * readObject is called to restore the state of the StringBuffer from
599 private void readObject(java.io.ObjectInputStream s)
600 throws java.io.IOException, ClassNotFoundException {
601 java.io.ObjectInputStream.GetField fields = s.readFields();
602 value = (char[])fields.get("value", null);
603 count = fields.get("count", 0);