Java Swing libaray 出现奇怪的渲染问题

Question

Background I want to create a GUI application using the java swing library. For layout I require it to be a GridLayout as the program outline requires this.

Aim To render a panel with text inside it.

What I have tired

• Using setBounds to move the text - this worked and the text did render, however it does not work with the GridLayout therefore does not meet the required specs.
• Reading atricles and documentation on GridLayout and rendering of JLabels - Tried the examples - failed.
• Using intellij debugger - results show the JLabel is not null, and the text is set to the correct value, along with the enabled and visible properties being true.
• Increasing and decreasing GirdLayout rows and columns - failed.
• Altering the size of the panel - failed.
• Changing the foreground colour to something like green - failed.

Code

public class MainPanel extends JPanel {
    public MainPanel(JFrame frame) {
        setBounds(40,40,200,200);
        setBackground(Color.BLUE);

        JLabel label = new JLabel("Hello World", SwingConstants.CENTER);
        label.setFont(new Font("Tahoma", Font.PLAIN, 25));
        label.setVisible(true);
        add(label);

        setLayout(new GridLayout(1, 1));
    }

}

Result

Conclusion As you can see, the panel does render (the blue square), however there is no text inside of it. I'm rather confused as code very similar to this has worked on aother project, and there is no obvious reason this shouldn't work.

Answer 1

Your code is essentially OK with the provisos I mentioned. Proof: (obviously you can separate out your own class as a top level one later):

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;


public class F extends JFrame {
    private void setGui() {
        try {
            setLocation(0, 100);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setContentPane(new MainPanel());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        try {
            EventQueue.invokeAndWait(() -> {
                F f = new F();
                f.setGui();
                f.setSize(200, 200);
                f.setVisible(true);
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}
class MainPanel extends JPanel {
    public MainPanel() {
        setLayout(new GridLayout(1, 1));
        setBounds(40,40,200,200);
        setBackground(Color.BLUE);
        JLabel label = new JLabel("Hello World", SwingConstants.CENTER);
        label.setFont(new Font("Tahoma", Font.PLAIN, 25));
        add(label);
    }

}