Java——String，StringBuffer,StringBuilder

String 一经创建，不可更改，每次更改都是创建新对象，销毁旧对象

StringBuilder 创建后可修改，多线程不安全

StringBuffer 创建后可修改，多线程安全

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()