question: public void init ( ForceSimulator fsim ) { clear ( ) ; float x1 = Float . MAX_VALUE , y1 = Float . MAX_VALUE ; float x2 = Float . MIN_VALUE , y2 = Float . MIN_VALUE ; Iterator itemIter = fsim . getItems ( ) ; while ( itemIter . hasNext ( ) ) { ForceItem item = ( ForceItem ) itemIter . next ( ) ; float x = item . location [ 0 ] ; float y = item . location [ 1 ] ; if ( x < x1 ) x1 = x ; if ( y < y1 ) y1 = y ; if ( x > x2 ) x2 = x ; if ( y > y2 ) y2 = y ; } float dx = x2 - x1 , dy = y2 - y1 ; if ( dx > dy ) { y2 = y1 + dx ; } else { x2 = x1 + dy ; } setBounds ( x1 , y1 , x2 , y2 ) ; itemIter = fsim . getItems ( ) ; while ( itemIter . hasNext ( ) ) { ForceItem item = ( ForceItem ) itemIter . next ( ) ; insert ( item ) ; } calcMass ( root ) ; }
target:  Initialize the simulation with the provided enclosing simulation. After this call has been made, the simulation can be queried for the  n-body force acting on a given item.