Why is making a class static changing the font and background color?

Question

I have 2 classes, a MainClass and a AdminPage. The AdminPage only consists of a JLabel with the text AdminPage. I use the Nimbus Look & Feel.

If I create a new AdminPage and put it into the MainClass it looks like this:

AdminPage adminPage = new AdminPage();

But if I change the modifier of the AdminPage to static, the font becomes bold and the background changes:

static AdminPage adminPage = new AdminPage();

I really dont understand why this is happening. It's causing me no problems, but a lot of confusion. I suppose this has something to do with how the UIManager sets the Look and Feel, but I cant pinpoint the exact cause.

Explanations would be appreciated!

---

Here is my mcve-Code:

MainClass.java:

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import net.miginfocom.swing.MigLayout;

public class MainClass extends JFrame {
    private static final long serialVersionUID = 1L;

    JPanel centerPanel = new JPanel();
    AdminPage adminPage = new AdminPage();

    public MainClass() {
        setBounds(300, 50, 300, 300);
        setLayout(new MigLayout());
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        centerPanel.setLayout(new MigLayout());
        centerPanel.add(adminPage);
        add(centerPanel, "growx, wrap");
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");

                    MainClass window = new MainClass();
                    window.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

AdminPage.java:

import javax.swing.JLabel;
import javax.swing.JPanel;
import net.miginfocom.swing.MigLayout;

public class AdminPage extends JPanel {
    private static final long serialVersionUID = 1L;

    JPanel contentPanel = new JPanel();
    JLabel testLabel = new JLabel("Adminpage");

    public AdminPage() {
        setLayout(new MigLayout());
        contentPanel.setLayout(new MigLayout());

        contentPanel.add(testLabel);
        add(contentPanel);
    }
}

EDIT:

Thanks to a comment from Henning Luther I've tried to initialize the UIManager in a static way:

static {
    try {
        UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
    }
    catch (Exception ex) {
    }
}

But my class still does not use the intended L&F.

Answer 1

You set the Look&Feel after the AdminPage is instantiated, that's why is not applied to it. The Look&Feel is not changed for all existing UI instances when setting in the UIManager. Since you set AdminPage to static its instantiated on class loading and before main is executed.