JPanel显示在JFrame的右下角

Question

I am trying to add a MessagePanel which extends JPanel into a JFrame so that it is simply in the center and takes up the whole thing, which I have done many times before but now for some reason it is appearing in the bottom right quarter of the JFrame and I can't figure out why. I added a border around it so i could see where it is. Anybody know what's wrong ?

import javax.swing.*;
import java.awt.*;

public class Book extends JFrame{

    public Book(){
        setLayout(new BorderLayout());
        add(new MessagePanel("My Message"), BorderLayout.CENTER);
    }

    public static void main(String[] args){
        Book f = new Book();
        f.setDefaultCloseOperation(Book.EXIT_ON_CLOSE);
        f.setTitle("Title");
        f.setSize(500, 500);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}

//

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;


public class MessagePanel extends JPanel{
    private String message = "";
    private boolean centered;
    private int x = 20;
    private int y = 20;
    private int interval = 10;

    public MessagePanel(){
    }

    public MessagePanel(String message){
        this.message = message;
        this.centered = true;
        setBorder(new LineBorder(Color.BLACK, 2));
    }

    public void setMessage(String message){
        this.message = message;
        repaint();
    }

    public void setCentered(boolean centered){
        this.centered = centered;
        repaint();
    }

    public void setX(int x){
        this.x = x;
        repaint();
    }

    public void setY(int y){
        this.y = y;
        repaint();
    }

    public int getX(){
        return x;
    }

    public int getY(){
        return y;
    }

    public void setInterval(int interval){
        this.interval = interval;
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g){
        super.paintComponent(g);

        if(centered){
            FontMetrics fontMetrics = g.getFontMetrics();
            x = (getWidth() / 2) - (fontMetrics.stringWidth(message) / 2);
            y = (getHeight() / 2) + (fontMetrics.getAscent() / 2);

        }
        g.drawString(message, x, y);

    }

    public void moveUp(){
        this.y -= interval;
        repaint();
    }

    public void moveDown(){
        this.y += interval;
        repaint();
    }

    public void moveLeft(){
        this.x -= interval;
        repaint();
    }

    public void moveRight(){
        this.x += interval;
        repaint();
    }
}

Answer 1

Don't override getX(), setX(...), getY() and setY(...).

Those are methods of the Component class and are used to control the location of the component.

If you want to control the location of the text then use different variables.