为什么Swing frame有时在下面没有打开？我附上了我的代码，有人帮我解释为什么会这样？

Question

在这里，我附上了我的代码：我现在正在开发我想要创建的音乐播放器，所以我在Swing FrameWork上编码此代码可以正常工作，然后添加两个名为上一个按钮和下一个播放按钮的按钮，添加这些按钮后，摆动框架没有打开，即使我尝试通过评论新添加的行（上一个按钮和下一个按钮），但这对我没有帮助

//Main Method
import javax.swing.JFrame;
import javax.swing.SwingUtilities;`

public class App{
public static void main(String args[]){
    SwingUtilities.invokeLater(new Runnable() { //To make Robust
        public void run(){  //Run Method
            new MainFrame();        }
    });
}
}
//Frame Method
import java.awt.BorderLayout;
import java.awt.event.*;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextArea;
import java.awt.FlowLayout;
public class MainFrame extends JFrame{
private JButton Play,Previous,Next;
private JTextArea textArea;
public MainFrame(){
    super("Hello World"); //Inherit that Jframe

    try{

    setLayout(new BorderLayout()); //Setting Layout
    setLayout(new FlowLayout());





    Play=new JButton("Play"); //Creating Object for Button

    Previous=new JButton("Previous");

    Next=new JButton("Next");



    textArea=new JTextArea();//Creating object for JTextArea

    Play.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent l) {
            textArea.append("Song plays\n");//Print Song Plays
        }
    });


Previous.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent l){
        textArea.append("Previous Song\n");
    }
});

Next.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent l){
        textArea.append("Next Song\n");
    }
});
//Adding TextArea and Buttons to Frame
    add(Play,FlowLayout.CENTER);//Adding to Frame
    add(textArea,FlowLayout.LEADING);//Adding to Frame
    add(Previous,FlowLayout.LEFT);
    add(Next,FlowLayout.RIGHT);

  


    setSize(800,800);//Size for Frame
    setResizable(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
}
catch( Exception e){
e.printStackTrace();
}
}
}

Answer 1

Oracle提供了一个有用的教程，使用Swing创建GUI。跳过NetBeans IDE部分的学习摆动。特别注意容器部分内的组件布局。

我继续创建了以下GUI。

创建Swing GUI时，将Swing组件添加到JPanel或JScrollPane。将jpanel和/或JScrollPanes添加到JFrame中。这有助于保持代码的条理化。

Swing布局管理器使创建GUI变得简单。将Swing组件添加到一个或多个JPanel，将JPanel添加到JFrame，然后打包JFrame。

我使用的唯一“技巧”是将最大的按钮的首选大小复制到其他按钮。这使GUI看起来更好。

这是完整的可运行代码。

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class MusicPlayer implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new MusicPlayer());
    }

    private JTextArea textArea;

    @Override
    public void run() {
        JFrame frame = new JFrame("Music Player");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(createTextArea(), BorderLayout.CENTER);
        frame.add(createButtonPanel(), BorderLayout.SOUTH);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JScrollPane createTextArea() {
        JPanel panel = new JPanel(new BorderLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

        textArea = new JTextArea(10, 40);
        panel.add(textArea, BorderLayout.CENTER);

        JScrollPane scrollPane = new JScrollPane(panel);

        return scrollPane;
    }

    private JPanel createButtonPanel() {
        JPanel panel = new JPanel(new FlowLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

        JButton previousButton = new JButton("Previous");
        previousButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                textArea.append("Previous Song\n");
            }
        });
        panel.add(previousButton);

        JButton playButton = new JButton("Play");
        playButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                textArea.append("Song plays\n");// Print Song Plays
            }
        });
        panel.add(playButton);

        JButton nextButton = new JButton("Next");
        nextButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                textArea.append("Next Song\n");
            }
        });
        panel.add(nextButton);

        // Make the buttons the same size
        Dimension d = previousButton.getPreferredSize();
        playButton.setPreferredSize(d);
        nextButton.setPreferredSize(d);

        return panel;
    }

}