public BasicGravity(GravityState state, Universe universe) {
this.state = state;
this.universe = universe;
this.fallingLeaves = new HashSet<TreeLeaf>();
this.gravity3D = new BasicGravity3D(state.getGravity3D(), universe.getUniverse3D());
Set<TreeLeafState> fallingLeafStates = state.getFallingLeaves();
for (TreeLeafState fallingLeafState : fallingLeafStates) {
addFallingLeaf(new BasicTreeLeaf(universe, fallingLeafState));
}
}