Problem:
  StringBuffer has methods for inserting and appending contents, but there
  is no direct and efficient way to delete, modify, or extract the contents
  of a StringBuffer. StringBuffer currently has a parallel structure between
  its existing appends and inserts except that there is no existing
  insert(int, char[], int, int); The lack of this insert operation may force
  a programmer to convert the StringBuffer to a String before the mutational
  operations are complete, hurting their performance.
 
Requestors:
  Tim Budd
  Chris Tomkins, IBM
  Anthony Sabatini, Cash Markets Group
  Charles Kerr, OAO Corp.
  Steve Olechowski, Digital Knowledge Assets
  Kevin McIsaac, South Branch Software
  Vartan Piroumian, vartan.com

Proposed API change:
    Add to class StringBuffer the following six operations to support
    minimal-but-useful, reasonably fast string processing:

  1. public StringBuffer delete(int start, int end)
  2. public StringBuffer deleteCharAt(int pos)
  3. public StringBuffer replace(int start, int end, String str)
  4a. public String substring(int start, int end)
  4b. public String substring(int start)
  5. public StringBuffer insert(int pos, char chars[], int offset, int len)

      This will fill out the following functionality matrix:

MODE: character-wise range-wise
      OP -------------- ----------
    append | append(ch) append(str)
    insert | insert(pos, ch) insert(pos, str)
    delete | deleteCharAt(pos)[NEW] delete(start, end)[NEW]
    replace | setCharAt(pos, ch) replace(start, end, str)[NEW]
    extract | charAt(pos) substring(start, end)[NEW]


  Notes:
   - The range-wise operations provide full-speed access to S.B. internals.
   - Substring is necessary to avoid recopying the entire buffer.
   - Deletion is totally absent in the 1.1 StringBuffer class!
   - Rangewise delete and replace operations allow end > length (cf. indexOf).
   - 4a/4b match the pre-existing design of String.substring.
   - 5 matches pre-existing StringBuffer.append design (see below).
   - Insert/append of char arrays integrates with JDK 1.1 character I/O.
   - Considered & rejected: searching, matching, case-folding, byte-conversion.

OP: append insert
     INPUT ------ ------
    String append(str) insert(pos, str)
    char[] append(chars) insert(pos, chars)
    char[]part append(chars,off,len) insert(pos, chars,off,len)[NEW]
    Object append(obj) insert(pos, obj)
    (any prim) append(primval) insert(pos, primval)