On my application I got the frame containing a JSplitPane. The JSplitPane is set to split horizontally. On left side there is a panel containing some components that do not matter.
On the right I got a JPanel(BoxLayout) containing subclass of JTextArea inside a JScrollPane,a JTextPane inside a JScrollPane, and a JButton.
My problem is how I get the components(mainly on the right) to resize, based on interaction with JSplitPane. So when the JSplitPane is dragged to the left, my JTextArea and JTextPane get wider.
I have tried different setups, also setting the preferredSize and MaximumSize but none of this seems to work. Components stay at their preferredSize. If I try to make them smaller the scrollPane works (which is fine) but when I try to get them bigger they stay at preferred size.
Most likely your problem is due to the BoxLayout used on your right panel. Copy-paste from the class javadoc:
BoxLayout attempts to arrange components at their preferred widths (for horizontal layout) or heights (for 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
Use another layout which scales the inner components. For example the CENTER area of a BorderLayout has such behavior.