Set size of JLabel in FlowLayout

Question

I have a JPanel that uses FlowLayout. I add a number of JLabels to the JPanel, use setPreferedSize() to adjust their size and save them in a list, label_list. Everything works fine. Then I want to change their size:

for(JLabel c:label_list){
c.setPreferedSize(new Dimension(10,10));
}

And it doesn't work.

c.setBackground(Color.red)

and similar stuff works. Why can't I use setPreferedSize here?

c.setBounds(1,1,10,10) and c.setSize(10,10) Works, but after i update the UI (resizeing the panel) every size goes back to normal.

Answer 1

Then I want to change their size:

for(JLabel c:label_list){ c.setPreferedSize(new Dimension(10,10)); }

And it doesn't work.

You need to call revalidate() on the parent of the labels so that it reperforms layout and enforces their preferred size.

c.setBounds(1,1,10,10) and c.setSize(10,10) Works, but after i update the UI (resizeing the panel) every size goes back to normal.

Setting bounds/size/location manually conflicts with the LayoutManager of the parent container. The job of the LayoutManager is to position and size the child components.

Either set the layout to null and call yourself setSize-setLocation/setBounds, or use a LayoutManager (recommended) and never call setSize-setLocation/setBounds. At most, you can call setPreferred/setMaximum/setMinimum size but try to avoid this as it can causes cross L&F problems.