It is a Java component, done by JGoodies.com and that distributes the graphical components by the screen, adapting to the changes of size.
The advantage of this component is that it is very easy to handle and to understand and that practicamente covers all the necessities with applications of windows with many fields and components.
One is based, in defining a grid, (of rows and columns), where the components are located. This allows that it is very easy to align the components. By each row or column we can specify its size, either fixed, or by which they say the components to us that contain it. Conditions can even be put, pej. "min(100, pref)" means the minimum between which they occupy the 100 components and pixels. In addition if we added ":grow" to a column (or row) we cause that this one changes of size adapting to the window. The components can occupy but of of a row or column, which is essential for great components like tables or trees.