我的Java Calculator程序中出现了奇怪的速度错误

Question

我用GUI创建了一个Java Calculator。我使用数组创建了按钮的JPanel，但我从一开始就注意到，当窗口出现时，按钮会在3-4秒后加载。我检查了一切，但找不到问题。这是代码：

主要

package main;

import ui.Calculator;

import javax.swing.*;

public class Main {
    public static void main(String[] args) {

        Calculator calculator = new Calculator();

        calculator.setVisible(true);
        calculator.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }
}

计算器

package ui;

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

public class Calculator extends JFrame {

    public Calculator() {
        super("Calculator");
        setSize(400, 400);
        setLocation(400, 400);
        setLayout(new BorderLayout());

        Buttons buttons = new Buttons();
        add(buttons);
    }
}

按钮 这就是我认为的问题根源

package ui;

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

/**
 * Creates a JPanel with the buttons that is going to be on the Window
 */
class Buttons extends JPanel{

    private static JButton[] numbers = new JButton[10];
    private static JButton bdot, bsum, bsubstract, bdivide, bmultiply, bequal;

    Buttons() {
        initializeButtons();
        JButton[] buttonNumbers = {numbers[7], numbers[8], numbers[9], bdivide, numbers[4], numbers[5], numbers[6], bmultiply,
                numbers[1], numbers[2], numbers[3], bsubstract, numbers[0], bdot, bsum, bequal};
        setLayout(new GridLayout(4, 4));
        int counter = 0;
        for (int y = 0; y < 4; y++) {
            for (int x = 0; x < 4; x++) {
                add(buttonNumbers[counter]);
                counter ++;
            }
        }
    }


    /**
     * Function that initialize all the buttons with their respective text
     */
    private static void initializeButtons() {
        for (int i = 0; i < numbers.length; i++) {
            numbers[i] = new JButton("" + i);
        }
        bdot = new JButton(".");
        bsum = new JButton("+");
        bsubstract = new JButton("-");
        bdivide = new JButton("/");
        bmultiply = new JButton("*");
        bequal = new JButton("=");
    }
}

注意：我知道还有其他方法可以做到这一点，但我找不到这种方法的问题，希望你能帮帮我，谢谢。