StringBuffer s = new StringBuffer();

StringBuffer s = new StringBuffer(“abc”);

StringBuffer s = “abc”;        //赋值类型不匹配
StringBuffer s = (StringBuffer)”abc”;  //不存在继承关系，无法进行强转

String s = “abc”;
StringBuffer sb1 = new StringBuffer(“123”);
StringBuffer sb2 = new StringBuffer(s);  //String转换为StringBuffer
String s1 = sb1.toString();       //StringBuffer转换为String

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 演示程序
 */
import java.util.HashMap;

public class StringBufferTest {

 public static void main(String[] args) {
  testInsertAPIs() ;
  testAppendAPIs() ;
  testReplaceAPIs() ;
  testDeleteAPIs() ;
  testIndexAPIs() ;
  testOtherAPIs() ;
 }

 /**
  * StringBuffer 的其它API示例
  */
 private static void testOtherAPIs() {

  System.out.println("-------------------------------- testOtherAPIs --------------------------------");

  StringBuffer sbuilder = new StringBuffer("0123456789");

  int cap = sbuilder.capacity();
  System.out.printf("cap=%d\n", cap);

  char c = sbuilder.charAt(6);
  System.out.printf("c=%c\n", c);

  char[] carr = new char[4];
  sbuilder.getChars(3, 7, carr, 0);
  for (int i=0; i<carr.length; i++)
   System.out.printf("carr[%d]=%c ", i, carr[i]);
  System.out.println();

  System.out.println();
 }

 /**
  * StringBuffer 中index相关API演示
  */
 private static void testIndexAPIs() {
  System.out.println("-------------------------------- testIndexAPIs --------------------------------");

  StringBuffer sbuilder = new StringBuffer("abcAbcABCabCaBcAbCaBCabc");
  System.out.printf("sbuilder=%s\n", sbuilder);

  // 1. 从前往后，找出"bc"第一次出现的位置
  System.out.printf("%-30s = %d\n", "sbuilder.indexOf(\"bc\")", sbuilder.indexOf("bc"));

  // 2. 从位置5开始，从前往后，找出"bc"第一次出现的位置
  System.out.printf("%-30s = %d\n", "sbuilder.indexOf(\"bc\", 5)", sbuilder.indexOf("bc", 5));

  // 3. 从后往前，找出"bc"第一次出现的位置
  System.out.printf("%-30s = %d\n", "sbuilder.lastIndexOf(\"bc\")", sbuilder.lastIndexOf("bc"));

  // 4. 从位置4开始，从后往前，找出"bc"第一次出现的位置
  System.out.printf("%-30s = %d\n", "sbuilder.lastIndexOf(\"bc\", 4)", sbuilder.lastIndexOf("bc", 4));

  System.out.println();
 }

 /**
  * StringBuffer 的replace()示例
  */
 private static void testReplaceAPIs() {

  System.out.println("-------------------------------- testReplaceAPIs ------------------------------");

  StringBuffer sbuilder;

  sbuilder = new StringBuffer("0123456789");
  sbuilder.replace(0, 3, "ABCDE");
  System.out.printf("sbuilder=%s\n", sbuilder);

  sbuilder = new StringBuffer("0123456789");
  sbuilder.reverse();
  System.out.printf("sbuilder=%s\n", sbuilder);

  sbuilder = new StringBuffer("0123456789");
  sbuilder.setCharAt(0, 'M');
  System.out.printf("sbuilder=%s\n", sbuilder);

  System.out.println();
 }

 /**
  * StringBuffer 的delete()示例
  */
 private static void testDeleteAPIs() {

  System.out.println("-------------------------------- testDeleteAPIs -------------------------------");

  StringBuffer sbuilder = new StringBuffer("0123456789");

  // 删除位置0的字符，剩余字符是“123456789”。
  sbuilder.deleteCharAt(0);
  // 删除位置3(包括)到位置6(不包括)之间的字符，剩余字符是“123789”。
  sbuilder.delete(3,6);

  // 获取sb中从位置1开始的字符串
  String str1 = sbuilder.substring(1);
  // 获取sb中从位置3(包括)到位置5(不包括)之间的字符串
  String str2 = sbuilder.substring(3, 5);
  // 获取sb中从位置3(包括)到位置5(不包括)之间的字符串，获取的对象是CharSequence对象，此处转型为String
  String str3 = (String)sbuilder.subSequence(3, 5);

  System.out.printf("sbuilder=%s\nstr1=%s\nstr2=%s\nstr3=%s\n", 
    sbuilder, str1, str2, str3);

  System.out.println();
 }

 /**
  * StringBuffer 的insert()示例
  */
 private static void testInsertAPIs() {

  System.out.println("-------------------------------- testInsertAPIs -------------------------------");

  StringBuffer sbuilder = new StringBuffer();

  // 在位置0处插入字符数组
  sbuilder.insert(0, new char[]{'a','b','c','d','e'});
  // 在位置0处插入字符数组。0表示字符数组起始位置，3表示长度
  sbuilder.insert(0, new char[]{'A','B','C','D','E'}, 0, 3);
  // 在位置0处插入float
  sbuilder.insert(0, 1.414f);
  // 在位置0处插入double
  sbuilder.insert(0, 3.14159d);
  // 在位置0处插入boolean
  sbuilder.insert(0, true);
  // 在位置0处插入char
  sbuilder.insert(0, '\n');
  // 在位置0处插入int
  sbuilder.insert(0, 100);
  // 在位置0处插入long
  sbuilder.insert(0, 12345L);
  // 在位置0处插入StringBuilder对象
  sbuilder.insert(0, new StringBuffer("StringBuilder"));
  // 在位置0处插入StringBuilder对象。6表示被在位置0处插入对象的起始位置(包括)，13是结束位置(不包括)
  sbuilder.insert(0, new StringBuffer("STRINGBUILDER"), 6, 13);
  // 在位置0处插入StringBuffer对象。
  sbuilder.insert(0, new StringBuffer("StringBuffer"));
  // 在位置0处插入StringBuffer对象。6表示被在位置0处插入对象的起始位置(包括)，12是结束位置(不包括)
  sbuilder.insert(0, new StringBuffer("STRINGBUFFER"), 6, 12);
  // 在位置0处插入String对象。
  sbuilder.insert(0, "String");
  // 在位置0处插入String对象。1表示被在位置0处插入对象的起始位置(包括)，6是结束位置(不包括)
  sbuilder.insert(0, "0123456789", 1, 6);
  sbuilder.insert(0, '\n');

  // 在位置0处插入Object对象。此处以HashMap为例
  HashMap map = new HashMap();
  map.put("1", "one");
  map.put("2", "two");
  map.put("3", "three");
  sbuilder.insert(0, map);

  System.out.printf("%s\n\n", sbuilder);
 }

 /**
  * StringBuffer 的append()示例
  */
 private static void testAppendAPIs() {

  System.out.println("-------------------------------- testAppendAPIs -------------------------------");

  StringBuffer sbuilder = new StringBuffer();

  // 追加字符数组
  sbuilder.append(new char[]{'a','b','c','d','e'});
  // 追加字符数组。0表示字符数组起始位置，3表示长度
  sbuilder.append(new char[]{'A','B','C','D','E'}, 0, 3);
  // 追加float
  sbuilder.append(1.414f);
  // 追加double
  sbuilder.append(3.14159d);
  // 追加boolean
  sbuilder.append(true);
  // 追加char
  sbuilder.append('\n');
  // 追加int
  sbuilder.append(100);
  // 追加long
  sbuilder.append(12345L);
  // 追加StringBuilder对象
  sbuilder.append(new StringBuffer("StringBuilder"));
  // 追加StringBuilder对象。6表示被追加对象的起始位置(包括)，13是结束位置(不包括)
  sbuilder.append(new StringBuffer("STRINGBUILDER"), 6, 13);
  // 追加StringBuffer对象。
  sbuilder.append(new StringBuffer("StringBuffer"));
  // 追加StringBuffer对象。6表示被追加对象的起始位置(包括)，12是结束位置(不包括)
  sbuilder.append(new StringBuffer("STRINGBUFFER"), 6, 12);
  // 追加String对象。
  sbuilder.append("String");
  // 追加String对象。1表示被追加对象的起始位置(包括)，6是结束位置(不包括)
  sbuilder.append("0123456789", 1, 6);
  sbuilder.append('\n');

  // 追加Object对象。此处以HashMap为例
  HashMap map = new HashMap();
  map.put("1", "one");
  map.put("2", "two");
  map.put("3", "three");
  sbuilder.append(map);
  sbuilder.append('\n');

  // 追加unicode编码
  sbuilder.appendCodePoint(0x5b57); // 0x5b57是“字”的unicode编码
  sbuilder.appendCodePoint(0x7b26); // 0x7b26是“符”的unicode编码
  sbuilder.appendCodePoint(0x7f16); // 0x7f16是“编”的unicode编码
  sbuilder.appendCodePoint(0x7801); // 0x7801是“码”的unicode编码

  System.out.printf("%s\n\n", sbuilder);
 }
}

-------------------------------- testInsertAPIs -------------------------------
{3=three, 2=two, 1=one}
12345StringBUFFERStringBufferBUILDERStringBuilder12345100
true3.141591.414ABCabcde

-------------------------------- testAppendAPIs -------------------------------
abcdeABC1.4143.14159true
10012345StringBuilderBUILDERStringBufferBUFFERString12345
{3=three, 2=two, 1=one}
字符编码

-------------------------------- testReplaceAPIs ------------------------------
sbuilder=ABCDE3456789
sbuilder=9876543210
sbuilder=M123456789

-------------------------------- testDeleteAPIs -------------------------------
sbuilder=123789
str1=23789
str2=78
str3=78

-------------------------------- testIndexAPIs --------------------------------
sbuilder=abcAbcABCabCaBcAbCaBCabc
sbuilder.indexOf("bc")   = 1
sbuilder.indexOf("bc", 5)  = 22
sbuilder.lastIndexOf("bc")  = 22
sbuilder.lastIndexOf("bc", 4) = 4

-------------------------------- testOtherAPIs --------------------------------
cap=26
c=6
carr[0]=3 carr[1]=4 carr[2]=5 carr[3]=6