question: public boolean add ( Object obj_ ) { _buf [ _bottom ] = obj_ ; _bottom = ( _bottom == _buf . length - 1 ) ? 0 : _bottom + 1 ; if ( _bottom == _top ) { int oldLen = _buf . length ; int newLen = oldLen * 2 ; Object [ ] newBuf = new Object [ newLen ] ; int topToEnd = oldLen - _top ; int newTop = newLen - topToEnd ; System . arraycopy ( _buf , 0 , newBuf , 0 , _top ) ; System . arraycopy ( _buf , _top , newBuf , newTop , topToEnd ) ; _buf = newBuf ; _top = newTop ; return true ; } return false ; }
target:  add an element to the bottom of the queue