Question

对于这个程序，除非你点击JButton所在的区域，否则JButton似乎不会出现; JFrame启动为空白。单击该按钮的那一刻，相应的代码就会运行，最后会显示该按钮。

如何在启动程序时显示按钮？

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;
/*
The Amazing BlackJack Advisory Tool by JoshK,HieuV, and AlvinC.
Prepare to be amazed :O
 */
public class BlckJackUI {
    //main class, will contain the JFrame of the program, as well as all the buttons.
    public static void main(String args[])
    {
    //Creating the JFrame
    JFrame GUI = new JFrame("Blackjack Advisor");
    GUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    GUI.setSize(1300, 900);
    GUI.setContentPane(new JLabel(new ImageIcon("C:\\Users\\Hieu Vo\\Desktop\\Green Background.png")));
    GUI.setVisible(true);
    // Because each button needs to run through the Math class.
    final Math math = new Math();
    // The Ace Button:
    ImageIcon Ace = new ImageIcon("/Users/computerscience2/Downloads/Ace.jpg");
    JButton ace = new JButton(Ace);
    ace.setSize(300, 100);
    ace.setLocation(100, 100);
    ace.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent e)
        {
            //Automatically default the the Ace to 11, and if Bust, Ace becomes 1. 
            if (math.array.playerhandtotal <= 21)
            {
                math.cardvalue = math.cardvalue + 11;
            }
            else
            {
                math.cardvalue = math.cardvalue + 1;
            }
            math.array.clicktracker++;
            math.calcResult();
            JOptionPane.showMessageDialog(null,math.array.result);
        }
    });
    GUI.add(ace);
    ImageIcon Two = new ImageIcon("/Users/computerscience2/Downloads/2.jpg");
    JButton two = new JButton(Two);
    two.setSize(300, 100);
    two.setLocation(100, 200);
    two.addActionListener(new ActionListener ()
    {
        public void actionPerformed(ActionEvent e)
        {
            /*
                This generally repeats throughout the whole class, and the only
                thing different is the changing cardvalue. When a button is pressed,
                respective cardvalues are added into the playerhand ArrayList, and
                totaled up to form playerhandtotal, which is a major factor in 
                bringing up the advice.
             */
            math.cardvalue = math.cardvalue + 2;
            math.array.clicktracker++;
            math.calcResult();
            JOptionPane.showMessageDialog(null,math.array.result);
        }
    });
    GUI.add(two);

等等，等等......只是一堆相同的东西，更多的按钮编码方式与JButton 2完全相同，但与它们有不同的值。

    JButton start = new JButton("Start/Reset");
    start.setSize(300, 100);
    start.setLocation(500,500);
    start.addActionListener(new ActionListener ()
    {
        public void actionPerformed(ActionEvent e)
        {
            /*
            The start button also acts like a reset button, and the concept is fairly
            simple. If we reset all the important values to 0 or "null," then the 
            program acts as if it was just opened.
             */
            Arrays array = new Arrays();
            array.playerhand.clear();
            array.dealer = 0;
            math.array.starttracker++;
            math.array.clicktracker = 0;
            array.playerhandtotal = 0;
            math.cardvalue = 0;
            array.result = null;
            JOptionPane.showMessageDialog(null,"Please select the card \nthat the dealer is showing :)");

        }
    });
    GUI.add(start);
    GUI.setLayout(null);

这一切都在同一个类中，我理解布局会更好，但也许有一种方法可以使用我现在拥有的东西解决这个问题？非常感谢任何想法。

Answer 1

程序开始为空，因为您在添加组件之前调用了setVisible。添加组件后（在构造函数的末尾）调用setVisible，它应该可以正常工作。此外，避免绝对定位并调用组件的set | Preferred | Minimum | MaximumSize方法。了解如何使用布局管理器。

Answer 2

不。问题是由布局引起的。在向JFrame或JPanel添加任何要具有绝对位置的东西之前，必须设置setLayout（null）。否则，您将始终有意外行为。经过三个小时的试验，我自己自己弄清楚了。突然，我将您的帖子与其他主题联系了起来，并且奏效了，但这在Internet上还没有得到很好的解释。

JButton在点击之前不会出现

2 个答案: