How to set only the preferred width of Panel with flow layout?

Question

I have a panel with flow layout, and it can contain a variable number of items - from 1 to 2000. I want to put it inside a scroll pane, scrollable in vertical direction, and with fixed width. The problem is, when I set preferred size of panel to something like (800,600), some items are missing, and there is no scroll. If I set up preferred size of scroll pane, then all elements in flow pane are put on one very long line.

Setting maximum size on any element seems to do nothing at all - layout managers ignore it.

How can I fix this?

Answer 1

I want to put it inside a scroll pane, scrollable in vertical direction, and with fixed width

You can use the Wrap Layout for this.

Don't set the preferred size of the panel. But you can set the preferred size of the scroll pane so the frame.pack() method will work.

Answer 2

You could use BoxLayout to do this:

JPanel verticalPane = new JPanel();
verticalPane.setLayout(new BoxLayout(verticalPane, BoxLayout.Y_AXIS));

JScrollPane pane = new JScrollPane(verticalPane);

//add what you want to verticalPane
verticalPane.add(new JButton("foo"));
verticalPane.add(new JButton("bar"));

This of course will use the preferred size of each component added. If you want to modify the preferred size for example of a JPanel, extend it and override getPreferredSize:

class MyPanel extends JPanel(){
    public Dimension getPreferredSize(){
         return new Dimension(100,100);
    }
} 

A note: BoxLayout will take in consideration getPreferredSize, other LayoutManager may not.

Please criticize my answer, I'm not sure it's completely correct and I'm curious to hear objections in order to know if I understood the problem.