Arrangement
How a Row or Column places its children along the axis it arranges them on, and how much space it leaves between two adjacent children.
An arrangement is handed the extent the container has along that axis together with the extent of each child, and answers with each child's position. The children keep the extent they asked for, so what an arrangement decides is where the space left over goes: Start, End, Top, Bottom and Center keep the children together and put all of it on one side or split it evenly; SpaceBetween, SpaceAround and SpaceEvenly share it out between them; spacedBy holds a fixed gap between adjacent children and places the group as a whole.
spacing is the gap an arrangement holds between two adjacent children. A container reserves it before it measures, so it is part of the size the container asks for.
Types
Arrangements for a Row that place children by physical position rather than reading order - the distinction Swing itself keeps between FlowLayout.LEFT and the reading-order FlowLayout.LEADING. Unlike their counterparts on Arrangement itself, none of these mirror the children's packing order under a right-to-left ComponentOrientation: they run left to right in declaration order whichever way the row reads. The two factories that take an Alignment.Horizontal are the exception - the alignment itself still resolves against the row's ComponentOrientation, so only the packing they align is absolute.
Places children along a horizontal axis, resolved against the container's ComponentOrientation.
Properties
Packs the children against the bottom.
Keeps the children together and puts half the space left over on either side of the group.
Packs the children against the trailing edge - the right under a left-to-right orientation.
Gives every child an equal gap of its own, so the gaps at the edges are half the gaps between.
Splits the space left over into equal gaps between the children, with none at either edge.
Splits the space left over into equal gaps between the children and at both edges.
Packs the children against the leading edge - the left under a left-to-right orientation.
Packs the children against the top.