question: public java . lang . StringBuffer insert ( int offset , char c ) { internal . insert ( offset , c ) ; return this ; }
target:  Inserts the string representation of the char argument into this string buffer. The second argument is inserted into the contents of this string buffer at the position indicated by offset. The length of this string buffer increases by one. The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then inserted into this StringBuffer object at the position indicated by offset. The offset argument must be greater than or equal to 0, and less than or equal to the length of this string buffer.