Java JLabel背景色不起作用？

Question

I'm learning how to create application in Java.

I'm having trouble getting the JLabel to have a background color whilst the JPanel is white, behind it. Also, is there a way to resize the JPanel to half of what the JFrame is?

Any help would be very much appreciated. Thank you.

---

   package PracticeOne;

    import java.awt.BorderLayout;

    public class PracticeOne {

        public static void main(String[] args) {


            Frame container = new Frame();
            Panel box = new Panel();
            Label txt = new Label();

            box.add(txt);

            container.add(box, BorderLayout.CENTER);


        }

    }

---

package PracticeOne;

import javax.swing.JFrame;

public class Frame extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    Frame(){        
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        this.setSize(500, 500);

        this.setVisible(true);

        this.setLocationRelativeTo(null);

        this.setTitle("Testing this out");
    }

}

---

package PracticeOne;

import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JPanel;

public class Panel extends JPanel {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;


    public Dimension d = new Dimension(100,100);

    Panel(){
        this.setSize(d);
        this.setAlignmentX(CENTER_ALIGNMENT);
        this.setBackground(Color.WHITE);

    }



}

---

package PracticeOne;

import java.awt.Color;

import javax.swing.JLabel;

public class Label extends JLabel {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;



    Label(){
        this.setSize(50, 50);


        this.setText("ya boy is working here");
        this.setForeground(Color.BLACK);
        this.setBackground(Color.ORANGE);

    }
}

Answer 1

I'm having trouble getting the JLabel to have a background color whilst the JPanel is white

You need to call setOpaque(true); in your JLabel

Also, is there a way to resize the JPanel to half of what the JFrame is?

You could use a GridLayout , and place 2 JPanel s in it, that way, you're going to have 2 JPanel s using half the size of your JFrame each.

Also, rename your classes, Panel belongs to the name of a class in AWT, same for Frame and Label , this might confuse your (and whoever reads your code).

Never extend JFrame , instead build your GUI based on JPanel s. See extends JFrame vs creating it inside of class and The use of multiple JFrames, Good / Bad practice? The general consensus says it's bad.

Also you should also check Should I avoid the use of setPreferred|Maximum|MinimumSize() in Swing? Again, yes, you should and instead override the getPreferredSize() method.

Don't forget to place your program on the Event Dispatch Thread (EDT) by changing your main() method as follows:

public static void main(String[] args) {
    //Java 8 with lambda expressions
    SwingUtilities.invokeLater(() -> 
        //Your code here
    );
    //Java 7 and below (Or 8 without lambda expressions)
    SwingUtilities.invokeLater(new Runnable() {
        //Your code here
    });
}

Now, with all the above recommendations, your code should now look like this:

import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class HalfSizePanelWithLabelInDifferentColor {

    private JFrame frame;
    private Container contentPane;
    private JPanel pane;
    private JPanel pane2;
    private JLabel label;

    private static final Dimension dim = new Dimension(100, 100);

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new HalfSizePanelWithLabelInDifferentColor().createAndShowGui());
    }

    public void createAndShowGui() {
        frame = new JFrame(getClass().getSimpleName());

        contentPane = frame.getContentPane();
        pane = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return dim;
            }
        };

        pane2 = new JPanel();

        pane.setOpaque(false);
        pane2.setOpaque(false);

        pane.setBorder(BorderFactory.createLineBorder(Color.RED));
        pane2.setBorder(BorderFactory.createLineBorder(Color.BLUE));

        label = new JLabel("Hello World!");
        label.setBackground(Color.GREEN);
        label.setOpaque(true);

        contentPane.setLayout(new GridLayout(2, 1));

        pane.add(label);

        contentPane.add(pane);
        contentPane.add(pane2);

        contentPane.setBackground(Color.WHITE);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

And your output would be like this:

Note that I added some colored borders to show where a pane starts and ends and where the other one starts and ends