# Java Notes

# BoxLayout and Boxes

BoxLayout arranges components either horizontally or vertically in a panel. You can control alignment and spacing of the components. Complicated layouts can be made by combining many panels, some with horizontal layout and some with vertical layouts.

Several classes are typically used: `javax.swing.BoxLayout`, `javax.swing.Box`, and `javax.swing.Box.Filler`.

## To Create a JPanel with BoxLayout

Choose either a horizontal layout (`BoxLayout.X_AXIS`) or vertical layout (`BoxLayout.Y_AXIS`) for a JPanel.

    JPanel p = new JPanel();
    p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
    p.add(some_component);

Unlike other layouts, the panel/container must be passed to the BoxLayout constructor.

## Example

The above examples were created with this code, using either X_AXIS or Y_AXIS.

    content.setLayout(new BoxLayout(content, BoxLayout.X_AXIS));
    content.add(new JButton("Button 1"));
    content.add(new JButton("2"));
    content.add(new JButton("This is button three"));

## The Box class

The `Box` class was designed to be a simple, and slightly more efficient, substitute for a `JPanel` with a `BoxLayout`. Because it doesn't support everything that `JPanel` does (eg, borders), I recommend using a `JPanel` with a `BoxLayout` rather than `Box`. However, the `Box` class has a number of necessary methods for working with `BoxLayouts`.

Because `Box` is a `Container` with `BoxLayout`, all discussions of spacing and alignment apply equally well to both JPanels with BoxLayouts and Boxes.

## Creating Boxes

You can create the two kinds of boxes with:

    import javax.swing.*;
    . . .
    Box vb = Box.createVerticalBox();
    Box hb = Box.createHorizontalBox();

## No Borders on Boxes

Boxes are lighter weight (ie, more efficient) than JPanel, but they don't support Borders. If you need borders, either use a JPanel with BoxLayout, or put the Box into a JPanel with a border.