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/*
Copyright 2006 by Sean Luke and George Mason University
Licensed under the Academic Free License version 3.0
See the file "LICENSE" for more information
*/
package sim.field.grid;
import sim.util.*;
/**
A wrapper for 2D arrays of Objects.
This object expects that the 2D arrays are rectangular. You are encouraged to access the array
directly. The object
implements all of the Grid2D interface. See Grid2D for rules on how to properly implement toroidal
or hexagonal grids.
The width and height of the object are provided to avoid having to say field[x].length, etc.
We very strongly encourage you to examine SparseGrid2D first to see if it's more appropriate to your task. If you need arbitrary numbers of Objects to be able to occupy the same location in the grid, or if you have very few Objects and a very large grid, or if your space is unbounded, you should probably use SparseGrid2D instead.
*/
public class ObjectGrid2D extends AbstractGrid2D
{
private static final long serialVersionUID = 1;
public Object[/**x*/][/**y*/] field;
public ObjectGrid2D (int width, int height)
{
this.width = width;
this.height = height;
field = new Object[width][height];
}
public ObjectGrid2D (int width, int height, Object initialValue)
{
this(width,height);
setTo(initialValue);
}
public ObjectGrid2D (ObjectGrid2D values)
{
setTo(values);
}
public ObjectGrid2D(Object[][] values)
{
setTo(values);
}
/** Sets location (x,y) to val */
public final void set(final int x, final int y, final Object val)
{
assert sim.util.LocationLog.it(this, new Int2D(x,y));
field[x][y] = val;
}
/** Returns the element at location (x,y) */
public final Object get(final int x, final int y)
{
assert sim.util.LocationLog.it(this, new Int2D(x,y));
return field[x][y];
}
/** Sets all the locations in the grid the provided element. WARNING:
this may conflict with setTo(Object[][]) -- make sure you have casted properly. */
public final ObjectGrid2D setTo(Object thisObj)
{
Object[] fieldx = null;
final int width = this.width;
final int height = this.height;
for(int x=0;xWARNING:
this may conflict with setTo(Object) -- make sure you have casted properly. */
public ObjectGrid2D setTo(Object[][] field)
{
// check info
if (field == null)
throw new RuntimeException("ObjectGrid2D set to null field.");
int w = field.length;
int h = 0;
if (w != 0) h = field[0].length;
for(int i = 0; i < w; i++)
if (field[i].length != h) // uh oh
throw new RuntimeException("ObjectGrid2D initialized with a non-rectangular field.");
// load
width = w;
height = h;
this.field = new Object[w][h];
for(int i = 0; i < w; i++)
this.field[i] = (Object[]) field[i].clone();
return this;
}
/** Flattens the grid to a one-dimensional array, storing the elements in row-major order,including duplicates and null values.
Returns the grid. */
public final Object[] toArray()
{
Object[][] field = this.field;
Object[] fieldx = null;
final int width = this.width;
final int height = this.height;
Object[] vals = new Object[width * height];
int i = 0;
for(int x=0;x0 && y>0 && xThen places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsMaxDistance(...)
* Returns the result Bag.
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may only run in two modes: toroidal or bounded. Unbounded lookup is not permitted, and so
* this function is deprecated: instead you should use the other version of this function which has more functionality.
* If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
The origin -- that is, the (x,y) point at the center of the neighborhood -- is always included in the results.
*
*
This function is equivalent to: getNeighborsMaxDistance(x,y,dist,toroidal ? Grid2D.TOROIDAL : Grid2D.BOUNDED, true, result, xPos, yPos);
*
* @deprecated
*/
public Bag getNeighborsMaxDistance( final int x, final int y, final int dist, final boolean toroidal, Bag result, IntBag xPos, IntBag yPos )
{
return getMooreNeighbors(x, y, dist, toroidal ? TOROIDAL : BOUNDED, true, result, xPos, yPos);
}
/**
* Gets all neighbors of a location that satisfy max( abs(x-X) , abs(y-Y) ) <= dist, This region forms a
* square 2*dist+1 cells across, centered at (X,Y). If dist==1, this
* is equivalent to the so-called "Moore Neighborhood" (the eight neighbors surrounding (X,Y)), plus (X,Y) itself.
* Places each x and y value of these locations in the provided IntBags xPos and yPos, clearing the bags first.
*
*
Then places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsMaxDistance(...)
* Returns the result Bag.
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getMooreNeighbors( final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos )
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getMooreLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
return getObjectsAtLocations(xPos,yPos,result);
}
/**
* Gets all neighbors of a location that satisfy max( abs(x-X) , abs(y-Y) ) <= dist. This region forms a
* square 2*dist+1 cells across, centered at (X,Y). If dist==1, this
* is equivalent to the so-called "Moore Neighborhood" (the eight neighbors surrounding (X,Y)), plus (X,Y) itself.
*
*
For each Object which falls within this distance, adds the X position, Y position, and Object into the
* xPos, yPos, and result Bag, clearing them first.
* Some positions may not appear
* and that others may appear multiply if multiple objects share that positions. Compare this function
* with getNeighborsMaxDistance(...).
* Returns the result Bag.
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getMooreNeighborsAndLocations(final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos)
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getMooreLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
reduceObjectsAtLocations( xPos, yPos, result);
return result;
}
/**
* Gets all neighbors of a location that satisfy abs(x-X) + abs(y-Y) <= dist. This region forms a diamond
* 2*dist+1 cells from point to opposite point inclusive, centered at (X,Y). If dist==1 this is
* equivalent to the so-called "Von-Neumann Neighborhood" (the four neighbors above, below, left, and right of (X,Y)),
* plus (X,Y) itself.
*
*
Places each x and y value of these locations in the provided IntBags xPos and yPos, clearing the bags first.
* Then places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsHamiltonianDistance(...)
* Returns the result Bag (constructing one if null had been passed in).
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may only run in two modes: toroidal or bounded. Unbounded lookup is not permitted, and so
* this function is deprecated: instead you should use the other version of this function which has more functionality.
* If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
The origin -- that is, the (x,y) point at the center of the neighborhood -- is always included in the results.
*
*
This function is equivalent to: getNeighborsHamiltonianDistance(x,y,dist,toroidal ? Grid2D.TOROIDAL : Grid2D.BOUNDED, true, result, xPos, yPos);
*
* @deprecated
*/
public Bag getNeighborsHamiltonianDistance( final int x, final int y, final int dist, final boolean toroidal, Bag result, IntBag xPos, IntBag yPos )
{
return getVonNeumannNeighbors(x, y, dist, toroidal ? TOROIDAL : BOUNDED, true,result, xPos, yPos);
}
/**
* Gets all neighbors of a location that satisfy abs(x-X) + abs(y-Y) <= dist. This region forms a diamond
* 2*dist+1 cells from point to opposite point inclusive, centered at (X,Y). If dist==1 this is
* equivalent to the so-called "Von-Neumann Neighborhood" (the four neighbors above, below, left, and right of (X,Y)),
* plus (X,Y) itself.
*
*
Places each x and y value of these locations in the provided IntBags xPos and yPos, clearing the bags first.
* Then places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsHamiltonianDistance(...)
* Returns the result Bag (constructing one if null had been passed in).
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getVonNeumannNeighbors( final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos )
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getVonNeumannLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
return getObjectsAtLocations(xPos,yPos,result);
}
/**
* Gets all neighbors of a location that satisfy abs(x-X) + abs(y-Y) <= dist. This region forms a diamond
* 2*dist+1 cells from point to opposite point inclusive, centered at (X,Y). If dist==1 this is
* equivalent to the so-called "Von-Neumann Neighborhood" (the four neighbors above, below, left, and right of (X,Y)),
* plus (X,Y) itself.
*
*
For each Object which falls within this distance, adds the X position, Y position, and Object into the
* xPos, yPos, and result Bag, clearing them first.
* Some positions may not appear
* and that others may appear multiply if multiple objects share that positions. Compare this function
* with getNeighborsMaxDistance(...).
* Returns the result Bag.
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getVonNeumannNeighborsAndLocations(final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos)
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getVonNeumannLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
reduceObjectsAtLocations( xPos, yPos, result);
return result;
}
/**
* Gets all neighbors located within the hexagon centered at (X,Y) and 2*dist+1 cells from point to opposite point
* inclusive.
* If dist==1, this is equivalent to the six neighbors immediately surrounding (X,Y),
* plus (X,Y) itself.
*
*
Places each x and y value of these locations in the provided IntBags xPos and yPos, clearing the bags first.
* Then places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsHamiltonianDistance(...)
* Returns the result Bag (constructing one if null had been passed in).
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may only run in two modes: toroidal or bounded. Unbounded lookup is not permitted, and so
* this function is deprecated: instead you should use the other version of this function which has more functionality.
* If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
The origin -- that is, the (x,y) point at the center of the neighborhood -- is always included in the results.
*
*
This function is equivalent to: getNeighborsHexagonalDistance(x,y,dist,toroidal ? Grid2D.TOROIDAL : Grid2D.BOUNDED, true, result, xPos, yPos);
*
* @deprecated
*/
public Bag getNeighborsHexagonalDistance( final int x, final int y, final int dist, final boolean toroidal, Bag result, IntBag xPos, IntBag yPos )
{
return getHexagonalNeighbors(x, y, dist, toroidal ? TOROIDAL : BOUNDED, true, result, xPos, yPos);
}
/**
* Gets all neighbors located within the hexagon centered at (X,Y) and 2*dist+1 cells from point to opposite point
* inclusive.
* If dist==1, this is equivalent to the six neighbors immediately surrounding (X,Y),
* plus (X,Y) itself.
*
*
Places each x and y value of these locations in the provided IntBags xPos and yPos, clearing the bags first.
* Then places into the result Bag any Objects which fall on one of these locations, clearning it first.
* Note that the order and size of the result Bag may not correspond to the X and Y bags. If you want
* all three bags to correspond (x, y, object) then use getNeighborsAndCorrespondingPositionsHamiltonianDistance(...)
* Returns the result Bag (constructing one if null had been passed in).
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getHexagonalNeighbors( final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos )
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getHexagonalLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
return getObjectsAtLocations(xPos,yPos,result);
}
/**
* Gets all neighbors located within the hexagon centered at (X,Y) and 2*dist+1 cells from point to opposite point
* inclusive.
* If dist==1, this is equivalent to the six neighbors immediately surrounding (X,Y),
* plus (X,Y) itself.
*
*
For each Object which falls within this distance, adds the X position, Y position, and Object into the
* xPos, yPos, and result Bag, clearing them first.
* Some positions may not appear
* and that others may appear multiply if multiple objects share that positions. Compare this function
* with getNeighborsMaxDistance(...).
* Returns the result Bag.
* null may be passed in for the various bags, though it is more efficient to pass in a 'scratch bag' for
* each one.
*
* This function may be run in one of three modes: Grid2D.BOUNDED, Grid2D.UNBOUNDED, and Grid2D.TOROIDAL. If "bounded",
* then the neighbors are restricted to be only those which lie within the box ranging from (0,0) to (width, height),
* that is, the width and height of the grid. If "unbounded", then the neighbors are not so restricted. Note that unbounded
* neighborhood lookup only makes sense if your grid allows locations to actually be outside this box. For example,
* SparseGrid2D permits this but ObjectGrid2D and DoubleGrid2D and IntGrid2D and DenseGrid2D do not. Finally if "toroidal",
* then the environment is assumed to be toroidal, that is, wrap-around, and neighbors are computed in this fashion. Toroidal
* locations will not appear multiple times: specifically, if the neighborhood distance is so large that it wraps completely around
* the width or height of the box, neighbors will not be counted multiple times. Note that to ensure this, subclasses may need to
* resort to expensive duplicate removal, so it's not suggested you use so unreasonably large distances.
*
*
You can also opt to include the origin -- that is, the (x,y) point at the center of the neighborhood -- in the neighborhood results.
*/
public Bag getHexagonalNeighborsAndLocations(final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos)
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getHexagonalLocations( x, y, dist, mode, includeOrigin, xPos, yPos );
reduceObjectsAtLocations( xPos, yPos, result);
return result;
}
public Bag getRadialNeighbors( final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos )
{
return getRadialNeighbors(x, y, dist, mode, includeOrigin, Grid2D.ANY, true, result, xPos, yPos);
}
public Bag getRadialNeighborsAndLocations( final int x, final int y, final int dist, int mode, boolean includeOrigin, Bag result, IntBag xPos, IntBag yPos )
{
return getRadialNeighborsAndLocations(x, y, dist, mode, includeOrigin, Grid2D.ANY, true, result, xPos, yPos);
}
public Bag getRadialNeighbors( final int x, final int y, final int dist, int mode, boolean includeOrigin, int measurementRule, boolean closed, Bag result, IntBag xPos, IntBag yPos )
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getRadialLocations( x, y, dist, mode, includeOrigin, measurementRule, closed, xPos, yPos );
return getObjectsAtLocations(xPos,yPos,result);
}
public Bag getRadialNeighborsAndLocations( final int x, final int y, final int dist, int mode, boolean includeOrigin, int measurementRule, boolean closed, Bag result, IntBag xPos, IntBag yPos )
{
if( xPos == null )
xPos = new IntBag();
if( yPos == null )
yPos = new IntBag();
getRadialLocations( x, y, dist, mode, includeOrigin, measurementRule, closed, xPos, yPos );
reduceObjectsAtLocations( xPos, yPos, result);
return getObjectsAtLocations(xPos,yPos,result);
}
// For each location, puts all such objects into the result bag. Modifies
// the xPos and yPos bags so that each position corresponds to the equivalent result in
// in the result bag.
void reduceObjectsAtLocations(final IntBag xPos, final IntBag yPos, Bag result)
{
if (result==null) result = new Bag();
else result.clear();
for( int i = 0 ; i < xPos.numObjs ; i++ )
{
assert sim.util.LocationLog.it(this, new Int2D(xPos.objs[i],yPos.objs[i]));
Object val = field[xPos.objs[i]][yPos.objs[i]] ;
if (val != null) result.add( val );
else
{
xPos.remove(i);
yPos.remove(i);
i--; // back up and try the object now in the new slot
}
}
}
/* For each location, puts all such objects into the result bag. Returns the result bag.
If the provided result bag is null, one will be created and returned. */
Bag getObjectsAtLocations(final IntBag xPos, final IntBag yPos, Bag result)
{
if (result==null) result = new Bag();
else result.clear();
for( int i = 0 ; i < xPos.numObjs ; i++ )
{
assert sim.util.LocationLog.it(this, new Int2D(xPos.objs[i],yPos.objs[i]));
Object val = field[xPos.objs[i]][yPos.objs[i]] ;
if (val != null) result.add( val );
}
return result;
}
}