为什么setLayout方法不能与JPanel的ArrayList一起使用

Question

I am quite new to swing and I had a question about layout managers. When I use setLayout() to put a layout manager in place for a single container I have no issues. Example:

JPanel oneContainer = new JPanel();
oneContainer.setLayout(new GridBagLayout());

This works fine.

What I want to do is set a certain layout manager for ever container in an ArrayList. Is there any way of doing this without cycling through each element with a loop.

Example:

ArrayList<JPanel> multipleContainers = new ArrayList<>();
multipleContainers.setLayout(new GridBagLayout());

(or something like that, you get the idea, I'm aware that the code provided is obviously erroneous, I'm also aware that to set a layout manager for a single ArrayList element I would just add .get(num) after the "multipleContainers") TIA

Answer 1

Sorry! You just have to suck it up and do it the hard way :) Actually it's not so hard with a for-each loop:

for (JPanel p : multipleContainers)
    p.setLayout(new GridBagLayout());

Or, as you've already surmised, there's the old-fashioned way:

for (int i = 0; i < multipleContainers.size(); ++i)
    multipleContainers.get(i).setLayout(new GridBagLayout());

Answer 2

I noticed that the type of multipleContainers is ArrayList, instead of JPanel. So setLayout() does not work here.

If you want to setLayout() works, you need to iterate the ArrayList to get panels.