java - 为什么在我将组件添加到 JFrame 而不是将它们添加到 JPanel 后，所有这些组件都消失了？

Question

当我将 JComboBox、JRadioButton、JButton 添加到 JPanel 时，它工作正常，但是当我将它们添加到 JFrame 并执行它后，所有这些组件都消失了。我的代码如下:

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

public class Test21 {
    public static void main(String[] args) {
        JFrame  jf = new JFrame("康樂彩歌(v0)");
        jf.setBounds(0, 0, 1368, 730);      
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel label1 = new JLabel("選歌：");    //創建標簽
        label1.setFont(new Font("新細明體", Font.PLAIN, 20));
        jf.add(label1);

        JComboBox cmbox = new JComboBox();    //創建JComboBox
        //cmb.setLocation(500,500);
        cmbox.setFont(new Font("新細明體", Font.PLAIN, 30));
        //cmb.setBounds(120,80,150,30);
        cmbox.addItem("紫竹調");
        cmbox.addItem("走一同去郊遊");
        cmbox.addItem("大野狼");
        cmbox.addItem("歸來吧蘇連多");
        cmbox.addItem("追尋");
        cmbox.addItem("三輪車");
        cmbox.addItem("我家門前有小河");
        cmbox.addItem("漁家樂");
        cmbox.addItem("嚕啦啦");
        cmbox.addItem("踏雪尋梅");
        jf.add(cmbox);

        JRadioButton rb2 = new JRadioButton("加人聲", false);
        rb2.setFont(new Font("新細明體", Font.PLAIN, 20));
        jf.add(rb2);

        JButton btPlay = new JButton("PLAY");
        btPlay.setFont(new Font(Font.DIALOG_INPUT, Font.BOLD, 25));
        jf.add(btPlay);

        //JButton btStop = new JButton("STOP");
        //btStop.setFont(new Font(Font.DIALOG_INPUT, Font.BOLD, 25));


        Panel1 jp1 = new Panel1();//Panel1() is a class included in the same project 
        jp1.setBorder(BorderFactory.createLineBorder(Color.black));
        jf.add(jp1);

        jp1.move = false;
        jp1.display();

        jf.setVisible(true);

        btPlay.addActionListener(new ActionListener() {//加上事件接收器-對按钮PLAY
           @Override
           public void actionPerformed(ActionEvent e) {//接收到事件後進行以下的處理
               Thread a = new Thread()
                  {
                    public void run()
                    {
                      AudioTest1 runAudio = new AudioTest1();//AudioTest1 is a class included in 
                                                               the same project.
                      runAudio.audioFileName = "audio1.wav";
                      runAudio.AudioPlay();
                    }
                  };
                Thread b = new Thread()
                  {
                    public void run()
                    {
                      jp1.move = true;
                      jp1.display();
                    }
                  };
                a.start();
                b.start();

              }
           });
    }
}

最初，我将这些组件作为 jp1.add(cmbox)、jp1.add(rb2)、jp1.add(btPlay) 添加到 JPanel，而不是 jf.add(cmbox)、jf.add(rb2)、jf。添加(btPlay)它工作正常。下面列出了Panel1.java:

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JButton;

import javax.swing.JPanel;

class Panel1 extends JPanel{    
    int x[] = new int[59]; //the x position of each note
    int y[] = new int[59]; //the y position of each note
    int width[] = new int[59]; //the width of each note
    int height = 20;           //the height of each note
    Color color[] = new Color[59];//the color of each note
    Boolean move;

    JButton btStop = new JButton("STOP");
    //btStop.setFont(new Font(Font.DIALOG_INPUT, Font.BOLD, 25));

    String[] lyric = {"一", " 根", "紫～", "竹", "直～", "苗～", "苗,", "送", "給", "寶", "寶", "做", "管", "簫,",
                      "簫", "兒", "對", "準", "口,", "口", "兒", "對", "準", "簫,", 
                      "簫～", "中", "吹～", "出", "新～", "時～ ", "調,",
                      "小", "寶～", "寶,", "小", "寶～", "寶,", 
                      "咿", "底", "咿", "底", "學 ", "會", "了,", "啊 ～     ～    ～"};//共45個

    int[] numNotes = {1, 1, 2, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 
                      1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
                      2, 1, 2, 1, 2, 2, 1,
                      1, 2, 1, 1, 2, 1, 
                      1, 1, 1, 1, 1, 1, 1, 6};//共45個

    int[][] notes = {{5,2},{8,2},{6,1},{5,1},{3,2},{5,1},{2,1},{3,1},{2,1},{1,4},{6,1},{8,1},
                     {3,1},{5,1},{6,2},{3,2},{5,8},{8,1},{6,1},{3,1},{6,1},{5,4},{6,1},{8,1},
                     {3,1},{6,1},{5,4},{5,1},{6,1},{8,2},{6,1},{5,1},{3,2},{5,1},{2,1},{3,1},
                     {2,1},{1,4},{1,2},{1,1},{3,1},{2,4},{1,2},{1,1},{3,1},{2,4},{6,1},{8,1},
                     {6,1},{8,1},{9,2},{6,2},{5,3},{6,1},{2,1},{3,1},{5,1},{6,1},{5,8}};//共59個

    String[] simplifiedNote = {"| 5", "  1", " 6", "5", "3", "| 5", "2", "3", "2", "1    - ", "| 6", "1", 
                               "3", "5", "6", " 3", "| 5    -     -     -", "| 1", "6", "3", "6", "5    - ", "| 6", "5", 
                               "3", "6", "5   -", "| 5", "6", "1", "6", "5", " 3", "| 5", "2", "3",
                               "2", "1    -", "| 1", "1", "3", "2    -", "| 1", "1", "3", "2    -", "| 6", "1", 
                               "6", "1", "2", "6", "| 5 ．", "6", "2", "3", "5", "6", "| 5     -     -     - "};//共59個

    Color color0 = new Color(255,255,255); //白色 
    Color color1 = new Color(255,0,0); //紅色
    Color color2 = new Color(255,165,0); //橙色
    Color color3 = new Color(255,255,0); //黃色
    Color color4 = new Color(0,128,0); //綠色
    Color color5 = new Color(0,0,255); //藍色
    Color color6 = new Color(75,0,130); //靛色
    Color color7 = new Color(100,0,153); //紫色
    Color color8 = new Color(153,0,0); //暗紅
    Color color9 = new Color(0,0,0); //黑色
    Color color10 = new Color(37,255,255); //淺藍

    public void display(){
        for (int i = 0;i < notes.length; i++) {
            //System.out.println("notes[" + i + "][0] = " + notes[i][0]);
            switch (notes[i][0]) {
                case 1:
                     y[i] = 400;
                     color[i] = color1;
                     break;
                case 2:
                     y[i] = 400 - 20;
                     color[i] = color2;
                     break;
                case 3:
                     y[i] = 400 - 20*2;
                     color[i] = color3;
                     break;
                case 4:
                     y[i] = 400 - 20*3;
                     color[i] = color4;
                     break;
                case 5:
                     y[i] = 400 - 20*4;
                     color[i] = color5;
                     break;
                case 6:
                     y[i] = 400 - 20*5;
                     color[i] = color6;
                     break;
                case 7:
                     y[i] = 400 - 20*6;
                     color[i] = color7;
                     break;
                case 8:
                     y[i] = 400 - 20*7;
                     color[i] = color1;
                     break;
                case 9:
                     y[i] = 400 - 20*8;
                     color[i] = color2;
            }

            switch (notes[i][1]) {
                case 1: width[i] = 20;     
                        break;
                case 2: width[i] = 20 * 2; 
                        break;
                case 3: width[i] = 20 * 3; 
                        break;
                case 4: width[i] = 20 * 4; 
                        break;
                case 5: width[i] = 20 * 5; 
                        break;
                case 6: width[i] = 20 * 6; 
                        break;
                case 7: width[i] = 20 * 7; 
                        break;
                case 8: width[i] = 20 * 8;
            }
        }

        x[0] = 100;
        for (int i = 1; i < notes.length; i++){
             x[i] = x[i-1] + width[i-1];
        }



        int timeLast = 0; //total executing time

        if (move == true) {
            while(timeLast < 900){ 
                for (int i = 0; i < notes.length; i ++){
                    x[i]--;
                }
                this.repaint(); 
                try {Thread.sleep(50);}
                catch (InterruptedException e){
                    e.printStackTrace();
                }
                timeLast = timeLast + 1; 
            }
        }
    }

    public void paint(Graphics g){
        super.paint(g); 
        Graphics2D g2d = (Graphics2D)g;

        g2d.setColor(color9); 
        g2d.setFont(new Font("新細明體", Font.BOLD, 20));

        int y1 = 130; //C調 4/4 Y坐標
        int y2 = 180; //簡譜行Y坐標
        int y3 = 210; //歌詞行Y坐標
        int y4 = 163; //加高音點
        int y5 = 180; //加八分音符底線
        int y6 = 470;  //色彩音符說明

        int chrPosition = 0;
        g2d.drawString("C調  4/4", 16, y1);

        //色彩音符說明
        g2d.drawString("色彩音符：", 16, y6);
        g2d.setColor(color1);

        g2d.fillRoundRect(126, y6-16, 20,20, 3,3);
        g2d.setColor(color9);
        g2d.drawString(": Do", 150, y6);//126 + 24
        g2d.setColor(color2);
        g2d.fillRoundRect(206, y6-16, 20,20, 3,3);//150 + 56
        g2d.setColor(color9);
        g2d.drawString(": Re", 230, y6);//206 + 24
        g2d.setColor(color3);
        g2d.fillRoundRect(286, y6-16, 20,20, 3,3);//230 + 56
        g2d.setColor(color9);
        g2d.drawString(": Mi", 310, y6);//286 + 24
        g2d.setColor(color4);
        g2d.fillRoundRect(366, y6-16, 20,20, 3,3);//310 + 56
        g2d.setColor(color9);
        g2d.drawString(": Fa",390, y6);//366 + 24
        g2d.setColor(color5);
        g2d.fillRoundRect(446, y6-16, 20,20, 3,3);//390 + 56
        g2d.setColor(color9);
        g2d.drawString(": So", 470, y6);//446 + 24
        g2d.setColor(color6);
        g2d.fillRoundRect(526, y6-16, 20,20, 3,3);//470 + 56
        g2d.setColor(color9);
        g2d.drawString(": La", 550, y6);//526 + 24
        //g2d.setColor(color7);
        //g2d.fillRoundRect(606, y6-16, 20,20, 3,3);//550 + 56
        //g2d.setColor(color9);
        //g2d.drawString(":Si", 630, y6);//606 + 24

        //寫出簡譜
        for (int i = 0;i < simplifiedNote.length; i++){

            g2d.drawString(simplifiedNote[i], x[i], y2);
        }

        //在簡譜下方寫出歌詞
        g2d.setColor(color9);
        for (int i = 0;  i < lyric.length; i++){
            if (i != 0 && numNotes[i-1] == 2) {
                chrPosition = chrPosition + 1;
                g2d.drawString(lyric[i], x[chrPosition], y3);
            }
            else {
                g2d.drawString(lyric[i], x[chrPosition], y3);
            }
            chrPosition = chrPosition + 1;
        }


        //在簡譜上方加高音點
        g2d.setColor(color9);
        g2d.drawString(".", x[1]+14, y4);
        g2d.drawString(".", x[11]+2, y4);
        g2d.drawString(".", x[17]+11, y4);
        //g2d.drawString(".", x[23]+2, y4);
        g2d.drawString(".", x[29]+2, y4);
        g2d.drawString(".", x[47]+2, y4);
        g2d.drawString(".", x[49]+2, y4);
        g2d.drawString(".", x[50]+2, y4);

        //在簡譜下方加八分音符底線
        g2d.setColor(color9);
        g2d.drawString("_", x[2]+4, y5);
        g2d.drawString("_", x[3], y5);
        g2d.drawString("_", x[5]+8, y5);
        g2d.drawString("_", x[6], y5);
        g2d.drawString("_", x[7], y5);//5
        g2d.drawString("_", x[8], y5);
        g2d.drawString("_", x[10]+8, y5);
        g2d.drawString("_", x[11], y5);
        g2d.drawString("_", x[12], y5);
        g2d.drawString("_", x[13], y5);//10
        g2d.drawString("_", x[17]+8, y5);
        g2d.drawString("_", x[18], y5);
        g2d.drawString("_", x[19], y5);
        g2d.drawString("_", x[20], y5);
        g2d.drawString("_", x[22]+8, y5);//15
        g2d.drawString("_", x[23], y5);
        g2d.drawString("_", x[24], y5);
        g2d.drawString("_", x[25], y5);
        g2d.drawString("_", x[27]+8, y5);
        g2d.drawString("_", x[28], y5);//20
        g2d.drawString("_", x[30], y5);
        g2d.drawString("_", x[31], y5);
        g2d.drawString("_", x[33]+8, y5);
        g2d.drawString("_", x[34], y5);
        g2d.drawString("_", x[35], y5);
        g2d.drawString("_", x[36], y5);//25
        g2d.drawString("_", x[39], y5);
        g2d.drawString("_", x[40], y5);
        g2d.drawString("_", x[43], y5);//1
        g2d.drawString("_", x[44], y5);//3
        g2d.drawString("_", x[46]+8, y5);//6
        g2d.drawString("_", x[47], y5);//1
        g2d.drawString("_", x[48], y5);//6
        g2d.drawString("_", x[49], y5);//1
        g2d.drawString("_", x[53], y5);//6
        g2d.drawString("_", x[54], y5);//2
        g2d.drawString("_", x[55], y5);//3
        g2d.drawString("_", x[56], y5);//5
        g2d.drawString("_", x[57], y5);//6

        //在歌詞下方繪出彩色譜        
        for (int i = 0;i < notes.length; i++){

            g2d.setColor(color[i]);
            g2d.fillRoundRect(x[i], y[i], width[i], height, 3,3); //畫圓角方塊

            g2d.setColor(color8);
            g2d.drawLine(x[i],230, x[i]+width[i], 230);//畫水平上線

            g2d.setColor(color8);
            g2d.drawLine(x[i],231, x[i], 429);//畫直紅線

            g2d.setColor(color8);
            g2d.drawLine(x[i],430, x[i]+width[i], 430);//畫水平下線
        }
        g2d.setColor(color8);
        g2d.drawLine(x[notes.length-1]+ width[notes.length - 1],231, x[notes.length - 1] + width[notes.length - 1],429);//畫邊界直紅線
    }
}

AudioTest1.java 列出如下:

import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;

class AudioTest1 {//to play the music
    String audioFileName; 
    public void AudioPlay() {

        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();

        try{
          Clip clip = AudioSystem.getClip();
          AudioInputStream inputStream = AudioSystem.getAudioInputStream(classLoader.getResourceAsStream(audioFileName));

              clip.open(inputStream);
              clip.start();
              while (!clip.isRunning())
                  Thread.sleep(0);
              while (clip.isRunning())
                  Thread.sleep(0);
              clip.close();
            } catch (Exception e)
                {
                  e.printStackTrace(); 
                  System.out.println(e); 
                }
    } 
}

我的目标是列出 JComboBox 中的所有歌曲，让用户选择一首歌曲并查看分数。单击“播放”按钮时，乐谱开始移动，同时播放音乐。

Answer 1

这是因为默认情况下 JPanel 使用 FlowLayout显示了一个接一个添加的组件

JFrame 使用 BorderLayout其中最多可放置 5 个组件(PAGE_START、PAGE_END、LINE_START、LINE_END、CENTER 区域各一个)。如果您不指定区域，则组件将被放置到 CENTER 区域中。如果您尝试将多个组件放入一个区域，最后一个组件将会显示。

对于您的问题，我建议创建一个 JPanel ，其中包含您的 JLabel、JComboBox、JRadioButton 和JButton 并将 JPanel 添加到 JFrame 中，如下所示:

JPanel buttonPanel = new JPanel();
buttonPanel.add(label1);  // instead of jf.add(label1);
buttonPanel.add(cmbox);   // instead of jf.add(cmbox);
buttonPanel.add(rb2);     // instead of jf.add(rb2);
buttonPanel.add(btPlay);  // instead of jf.add(btPlay);
jf.add(buttonPanel, BorderLayout.PAGE_START);

<小时/>

如果你这样做了，为什么你的组件不显示

jf.setLayout(null); 
jp1.setBounds(0, 100, 1368, 730);

这很简单:如果您想通过编写jf.setLayout(null);来使用绝对定位，您必须自己定义每个组件的边界。

而且这不能很好地扩展:这是一项乏味的任务，如果人们有不同的字体大小设置，你几乎肯定会让某人不高兴。

最好了解各种布局管理器如何工作并正确使用它们。要了解布局管理器，您可以在 https://docs.oracle.com/javase/tutorial/uiswing/layout/index.html 找到重要文档。