如何在Java swing中用背景色填充整个面板？

Question

I have recently started learning Java, and am now trying to work with Swing, so I am still rather new to this. I am trying to make a gridbaglayout with (in this example)1 row and 1 column, so I added a JPanel with some background color to the layout, however the background color seems to appear only for the length of the text, not for the entire panel. I would like for the background color to stay for the entire length of the row,

also, i had to add a second column with a large weightx to make sure my panel didnt get automatically centred, is there a better way to implement that?

This is the code that I currently have,

      public static void main(String args[]) {
            JFrame mainFrame = new JFrame();
            mainFrame.setSize(900, 600);
            mainFrame.setLayout(new GridBagLayout());

            JPanel roll = new JPanel();
            roll.setBackground(new Color(190, 177, 245));

            JLabel wageChangeTag = new JLabel("Change");

            GridBagConstraints gRoll = new GridBagConstraints();

            gRoll.gridx = 0;
            gRoll.gridy = 0;
            gRoll.weightx = 5;
            gRoll.anchor = GridBagConstraints.CENTER;
            roll.add(wageChangeTag, gRoll);

            ////////////// MAIN GRID//////////////////
            GridBagConstraints gc = new GridBagConstraints();
            gc.gridx = 0;
            gc.gridy = 0;
            gc.weightx = 5;
            gc.anchor = GridBagConstraints.FIRST_LINE_START;
            gc.weighty = 5;
            mainFrame.add(roll, gc);

            gc.gridx++;
            gc.weightx = 0.1;
            mainFrame.add(new JLabel(), gc);

            mainFrame.setVisible(true);
            mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      }
}

Answer 1

What you see painted is actually all your JPanel, nothing to do with your label inside it. You can see that for example by adding a border to it (right after you set the background :

roll.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.RAISED));

Now to have it expand horizontally , try adding the below line in your JPanel GridBagConstraints :

gc.fill = GridBagConstraints.HORIZONTAL;