public abstract void setGlassPane (Component glassPane)

The glassPane is always the first child of the rootPane and the rootPanes layout manager ensures that it's always as big as the rootPane. By default it's transparent and not visible. It can be used to temporarily grab all keyboard and mouse input by adding listeners and then making it visible. by default it's not visible.

The glassPane may not be null.

Generally implemented with getRootPane().setGlassPane(glassPane);

glassPane    the glass pane

See also:
getGlassPane, JRootPane.setGlassPane