JComponent background color using null layout?

Question

just a short question: Is it possible to add a background color to a JComponent when it is added directly onto a JFrame using null layout? The size and position of the component are set by setBounds() and i know that the background color will not be displayed using this setup. (I know you should always use layout managers, but in this case i want to prevent this).

[Why is it frowned upon to use a null layout in SWING?](http://stackoverflow.com/questions/6592468/why-is-it-frowned-upon-to-use-a-null-layout-in-swing) — MadProgrammer, Feb 16 '16 at 23:37
Java GUIs have to work on different OS', screen size, screen resolution etc. using different PLAFs in different locales. As such, they are not conducive to pixel perfect layout. Instead use layout managers, or [combinations of them](http://stackoverflow.com/a/5630271/418556) along with layout padding and borders for [white space](http://stackoverflow.com/a/17874718/418556). As an aside: most people around here that are worth listening to, will expect that people asking questions will fix the problem of `null` layouts (by using a layout) before seriously considering tackling other issues. — Andrew Thompson, Feb 17 '16 at 03:35

score 1 · Answer 1 · edited May 23 '17 at 12:15

JComponent is transparent by default, you'd either need to change its opaque state or use a JPanel

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.LineBorder;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                TestPane pane = new TestPane();
                pane.setBounds(10, 10, 100, 100);

                JFrame frame = new JFrame("Testing");
                frame.setLayout(null); // This is bad, but it proofs my point
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(pane);
                frame.setSize(200, 200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JComponent {

        public TestPane() {
            addMouseListener(new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {
                    setOpaque(!isOpaque());
                    repaint();
                }
            });
            setBackground(Color.BLUE);
            setBorder(new LineBorder(Color.RED));
        }

    }

}

null layouts are bad news, I don't condone them and you should avoid using them, the example above simply proves the point that it's the JComponents opaque state which needs to be changed

Why is it frowned upon to use a null layout in SWING? is a nice read about why you should avoid using null layouts.

If you want more control, write your own.

JComponent background color using null layout?

1 Answers1