本章介绍StringBuffer以及它的API的详细使用方法。
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StringBuffer 简介
StringBuffer 是一个线程安全的可变的字符序列。它继承于AbstractStringBuilder，实现了CharSequence接口。
StringBuilder 也是继承于AbstractStringBuilder的子类；但是，StringBuilder和StringBuffer不同，前者是非线程安全的，后者是线程安全的。
StringBuffer 和 CharSequence之间的关系图如下：
StringBuffer 函数列表
StringBuffer() StringBuffer(int capacity) StringBuffer(String string) StringBuffer(CharSequence cs) StringBuffer append(boolean b) StringBuffer append(int i) StringBuffer append(long l) StringBuffer append(float f) StringBuffer append(double d) synchronized StringBuffer append(char ch) synchronized StringBuffer append(char[] chars) synchronized StringBuffer append(char[] chars, int start, int length) synchronized StringBuffer append(Object obj) synchronized StringBuffer append(String string) synchronized StringBuffer append(StringBuffer sb) synchronized StringBuffer append(CharSequence s) synchronized StringBuffer append(CharSequence s, int start, int end) StringBuffer appendCodePoint(int codePoint) int capacity() synchronized char charAt(int index) synchronized int codePointAt(int index) synchronized int codePointBefore(int index) synchronized int codePointCount(int beginIndex, int endIndex) synchronized StringBuffer delete(int start, int end) synchronized StringBuffer deleteCharAt(int location) synchronized void ensureCapacity(int min) synchronized void getChars(int start, int end, char[] buffer, int idx) synchronized int indexOf(String subString, int start) int indexOf(String string) StringBuffer insert(int index, boolean b) StringBuffer insert(int index, int i) StringBuffer insert(int index, long l) StringBuffer insert(int index, float f) StringBuffer insert(int index, double d) synchronized StringBuffer insert(int index, char ch) synchronized StringBuffer insert(int index, char[] chars) synchronized StringBuffer insert(int index, char[] chars, int start, int length) synchronized StringBuffer insert(int index, String string) StringBuffer insert(int index, Object obj) synchronized StringBuffer insert(int index, CharSequence s) synchronized StringBuffer insert(int index, CharSequence s, int start, int end) int lastIndexOf(String string) synchronized int lastIndexOf(String subString, int start) int length() synchronized int offsetByCodePoints(int index, int codePointOffset) synchronized StringBuffer replace(int start, int end, String string) synchronized StringBuffer reverse() synchronized void setCharAt(int index, char ch) synchronized void setLength(int length) synchronized CharSequence subSequence(int start, int end) synchronized String substring(int start) synchronized String substring(int start, int end) synchronized String toString() synchronized void trimToSize()
StringBuffer源码(基于jdk1.7.40)
1 package java.lang; 2 3 public final class StringBuffer 4 extends AbstractStringBuilder 5 implements java.io.Serializable, CharSequence 6 { 7 8 static final long serialVersionUID = 3388685877147921107L; 9 10 public StringBuffer() { 11 super(16); 12 } 13 14 public StringBuffer(int capacity) { 15 super(capacity); 16 } 17 18 public StringBuffer(String str) { 19 super(str.length() + 16); 20 append(str); 21 } 22 23 public StringBuffer(CharSequence seq) { 24 this(seq.length() + 16); 25 append(seq); 26 } 27 28 public synchronized int length() { 29 return count; 30 } 31 32 public synchronized int capacity() { 33 return value.length; 34 } 35 36 37 public synchronized void ensureCapacity(int minimumCapacity) { 38 if (minimumCapacity > value.length) { 39 expandCapacity(minimumCapacity); 40 } 41 } 42 43 public synchronized void trimToSize() { 44 super.trimToSize(); 45 } 46 47 public synchronized void setLength(int newLength) { 48 super.setLength(newLength); 49 } 50 51 public synchronized char charAt(int index) { 52 if ((index < 0) || (index >= count)) 53 throw new StringIndexOutOfBoundsException(index); 54 return value[index]; 55 } 56 57 public synchronized int codePointAt(int index) { 58 return super.codePointAt(index); 59 } 60 61 public synchronized int codePointBefore(int index) { 62 return super.codePointBefore(index); 63 } 64 65 public synchronized int codePointCount(int beginIndex, int endIndex) { 66 return super.codePointCount(beginIndex, endIndex); 67 } 68 69 public synchronized int offsetByCodePoints(int index, int codePointOffset) { 70 return super.offsetByCodePoints(index, codePointOffset); 71 } 72 73 public synchronized void getChars(int srcBegin, int srcEnd, char[] dst, 74 int dstBegin) 75 { 76 super.getChars(srcBegin, srcEnd, dst, dstBegin); 77 } 78 79 public synchronized void setCharAt(int index, char ch) { 80 if ((index < 0) || (index >= count)) 81 throw new StringIndexOutOfBoundsException(index); 82 value[index] = ch; 83 } 84 85 public synchronized StringBuffer append(Object obj) { 86 super.append(String.valueOf(obj)); 87 return this; 88 } 89 90 public synchronized StringBuffer append(String str) { 91 super.append(str); 92 return this; 93 } 94 95 public synchronized StringBuffer append(StringBuffer sb) { 96 super.append(sb); 97 return this; 98 } 99 100 public StringBuffer append(CharSequence s) { 101 // Note, synchronization achieved via other invocations 102 if (s == null) 103 s = "null"; 104 if (s instanceof String) 105 return this.append((String)s); 106 if (s instanceof StringBuffer) 107 return this.append((StringBuffer)s); 108 return this.append(s, 0, s.length()); 109 } 110 111 public synchronized StringBuffer append(CharSequence s, int start, int end) 112 { 113 super.append(s, start, end); 114 return this; 115 } 116 117 public synchronized StringBuffer append(char[] str) { 118 super.append(str); 119 return this; 120 } 121 122 public synchronized StringBuffer append(char[] str, int offset, int len) { 123 super.append(str, offset, len); 124 return this; 125 } 126 127 public synchronized StringBuffer append(boolean b) { 128 super.append(b); 129 return this; 130 } 131 132 public synchronized StringBuffer append(char c) { 133 super.append(c); 134 return this; 135 } 136 137 public synchronized StringBuffer append(int i) { 138 super.append(i); 139 return this; 140 } 141 142 public synchronized StringBuffer appendCodePoint(int codePoint) { 143 super.appendCodePoint(codePoint); 144 return this; 145 } 146 147 public synchronized StringBuffer append(long lng) { 148 super.append(lng); 149 return this; 150 } 151 152 public synchronized StringBuffer append(float f) { 153 super.append(f); 154 return this; 155 } 156 157 public synchronized StringBuffer append(double d) { 158 super.append(d); 159 return this; 160 } 161 162 public synchronized StringBuffer delete(int start, int end) { 163 super.delete(start, end); 164 return this; 165 } 166 167 public synchronized StringBuffer deleteCharAt(int index) { 168 super.deleteCharAt(index); 169 return this; 170 } 171 172 public synchronized StringBuffer replace(int start, int end, String str) { 173 super.replace(start, end, str); 174 return this; 175 } 176 177 public synchronized String substring(int start) { 178 return substring(start, count); 179 } 180 181 public synchronized CharSequence subSequence(int start, int end) { 182 return super.substring(start, end); 183 } 184 185 public synchronized String substring(int start, int end) { 186 return super.substring(start, end); 187 } 188 189 public synchronized StringBuffer insert(int index, char[] str, int offset, 190 int len) 191 { 192 super.insert(index, str, offset, len); 193 return this; 194 } 195 196 public synchronized StringBuffer insert(int offset, Object obj) { 197 super.insert(offset, String.valueOf(obj)); 198 return this; 199 } 200 201 public synchronized StringBuffer insert(int offset, String str) { 202 super.insert(offset, str); 203 return this; 204 } 205 206 public synchronized StringBuffer insert(int offset, char[] str) { 207 super.insert(offset, str); 208 return this; 209 } 210 211 public StringBuffer insert(int dstOffset, CharSequence s) { 212 // Note, synchronization achieved via other invocations 213 if (s == null) 214 s = "null"; 215 if (s instanceof String) 216 return this.insert(dstOffset, (String)s); 217 return this.insert(dstOffset, s, 0, s.length()); 218 } 219 220 public synchronized StringBuffer insert(int dstOffset, CharSequence s, 221 int start, int end) 222 { 223 super.insert(dstOffset, s, start, end); 224 return this; 225 } 226 227 public StringBuffer insert(int offset, boolean b) { 228 return insert(offset, String.valueOf(b)); 229 } 230 231 public synchronized StringBuffer insert(int offset, char c) { 232 super.insert(offset, c); 233 return this; 234 } 235 236 public StringBuffer insert(int offset, int i) { 237 return insert(offset, String.valueOf(i)); 238 } 239 240 public StringBuffer insert(int offset, long l) { 241 return insert(offset, String.valueOf(l)); 242 } 243 244 public StringBuffer insert(int offset, float f) { 245 return insert(offset, String.valueOf(f)); 246 } 247 248 public StringBuffer insert(int offset, double d) { 249 return insert(offset, String.valueOf(d)); 250 } 251 252 public int indexOf(String str) { 253 return indexOf(str, 0); 254 } 255 256 public synchronized int indexOf(String str, int fromIndex) { 257 return String.indexOf(value, 0, count, 258 str.toCharArray(), 0, str.length(), fromIndex); 259 } 260 261 public int lastIndexOf(String str) { 262 // Note, synchronization achieved via other invocations 263 return lastIndexOf(str, count); 264 } 265 266 public synchronized int lastIndexOf(String str, int fromIndex) { 267 return String.lastIndexOf(value, 0, count, 268 str.toCharArray(), 0, str.length(), fromIndex); 269 } 270 271 public synchronized StringBuffer reverse() { 272 super.reverse(); 273 return this; 274 } 275 276 public synchronized String toString() { 277 return new String(value, 0, count); 278 } 279 280 private static final java.io.ObjectStreamField[] serialPersistentFields = 281 { 282 new java.io.ObjectStreamField("value", char[].class), 283 new java.io.ObjectStreamField("count", Integer.TYPE), 284 new java.io.ObjectStreamField("shared", Boolean.TYPE), 285 }; 286 287 private synchronized void writeObject(java.io.ObjectOutputStream s) 288 throws java.io.IOException { 289 java.io.ObjectOutputStream.PutField fields = s.putFields(); 290 fields.put("value", value); 291 fields.put("count", count); 292 fields.put("shared", false); 293 s.writeFields(); 294 } 295 296 private void readObject(java.io.ObjectInputStream s) 297 throws java.io.IOException, ClassNotFoundException { 298 java.io.ObjectInputStream.GetField fields = s.readFields(); 299 value = (char[])fields.get("value", null); 300 count = fields.get("count", 0); 301 } 302 }