A layout manager that allows multiple components to be laid out either vertically or horizontally. The components will not wrap so, for example, a vertical arrangement of components will stay vertically arranged when the frame is resized.

Nesting multiple panels with different combinations of horizontal and vertical gives an effect similar to GridBagLayout, without the complexity. The diagram shows two panels arranged horizontally, each of which contains 3 components arranged vertically.

The BoxLayout manager is constructed with an axis parameter that specifies the type of layout that will be done. There are four choices:

• X_AXIS - Components are laid out horizontally from left to right.
• Y_AXIS - Components are laid out vertically from top to bottom.
• LINE_AXIS - Components are laid out the way words are laid out in a line, based on the container's ComponentOrientation property. If the container's ComponentOrientation is horizontal then components are laid out horizontally, otherwise they are laid out vertically. For horizontal orientations, if the container's ComponentOrientation is left to right then components are laid out left to right, otherwise they are laid out right to left. For vertical orientations components are always laid out from top to bottom.
• PAGE_AXIS - Components are laid out the way text lines are laid out on a page, based on the container's ComponentOrientation property. If the container's ComponentOrientation is horizontal then components are laid out vertically, otherwise they are laid out horizontally. For horizontal orientations, if the container's ComponentOrientation is left to right then components are laid out left to right, otherwise they are laid out right to left.  For vertical orientations components are always laid out from top to bottom.

For all directions, components are arranged in the same order as they were added to the container.

BoxLayout attempts to arrange components at their preferred widths (for a horizontal layout) or heights (for a vertical layout).

For a horizontal layout, if not all the components are the same height, BoxLayout attempts to make all the components as high as the highest component. If that's not possible for a particular component, then BoxLayout aligns that component vertically, according to the component's Y alignment. By default, a component has a Y alignment of 0.5, which means that the vertical center of the component should have the same Y coordinate as the vertical centers of other components with 0.5 Y alignment.

Similarly, for a vertical layout, BoxLayout attempts to make all components in the column as wide as the widest component. If that fails, it aligns them horizontally according to their X alignments. For PAGE_AXIS layout, horizontal alignment is done based on the leading edge of the component. In other words, an X alignment value of 0.0 means the left edge of a component if the container's ComponentOrientation is left to right, and it means the right edge of the component otherwise.

Instead of using BoxLayout directly, many programs use the Box class. The Box class is a lightweight container that uses the BoxLayout layout manager. It also provides handy methods to help you use BoxLayout well. Adding components to multiple nested boxes is a powerful way to get the arrangement you want.

For further information and examples see How to Use BoxLayout, a section in The Java Tutorial.