public StrBuilder insert(int index,char value){
  validateIndex(index);
  ensureCapacity(size + 1);
  System.arraycopy(buffer,index,buffer,index + 1,size - index);
  buffer[index]=value;
  size++;
  return this;
}

public StrBuilder insert ( int index , char value ) { validateIndex ( index ) ; ensureCapacity ( size + 1 ) ; System . arraycopy ( buffer , index , buffer , index + 1 , size - index ) ; buffer [ index ] = value ; size ++ ; return this ; }
inserts the value into this builder .
