此代码有什么问题？ （JScrollPanel和JFrame）

Question

由于某种原因，当我运行此代码时，我的JFrame变成空白。我可能已经尝试在线教程一个小时了，我想知道我是否误解了。

代码如下：

public class Application {

    public static JFrame f;
    public static JButton submit;
    public static JTextField unscramblee;
    public static String scrambledWord, possibleWords;
    public static JLabel possibleWordsDisplay;
    public static JPanel UI;
    public static JScrollPane scrollPane;

    Application() {
        f = new JFrame("test");
        f.setResizable(true);
        f.setLayout(null);
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        UI = new JPanel();
        scrollPane = new JScrollPane(UI);
        unscramblee = new JTextField("test");
        unscramblee.setBounds(240, 200, 400, 50);
        submit = new JButton("Submit");
        submit.setBounds(240, 350, 400, 100);
        possibleWordsDisplay = new JLabel("possibleWordsDisplay - this is a display for words that are possible");
        possibleWordsDisplay.setBounds(240, 0, 200, 200);

        scrollPane.add(unscramblee);
        scrollPane.add(submit);
        scrollPane.add(possibleWordsDisplay);

        f.getContentPane().add(scrollPane);
        f.pack();
        f.setSize(1280,720);
    }
}

我希望这是足够的信息来提供帮助。谢谢。

（如果有人想知道为什么setSize方法在pack方法之后，这是因为JFrame在我运行时会不断崩溃。如果您也知道如何解决此问题，请告诉我！我将非常感谢。 ）

Answer 1

手动设置绑定范围不是可行的做法。
而是将适当的Layout Managers用于所需的布局。
以下是mre ¹ （请注意注释）：

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;

public class Application {

    Application() {
        JFrame f = new JFrame("test");
        //f.setSize(1280,720); f.pack  should automatically set the size  
        f.setResizable(true);
        //f.setLayout(null); do not use null layout
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel UI = new JPanel();  // uses flowlayout by default
        //UI.setBounds(0, 0, 1280, 720); do not set bounds. that the job of the layout manager

        JTextField unscramblee = new JTextField("test", 10);
        //unscramblee.setBounds(240, 200, 400, 50);
        JButton submit = new JButton("Submit");
        //submit.setBounds(240, 350, 400, 100);
        JLabel possibleWordsDisplay = new JLabel("possibleWordsDisplay - this is a display for words that are possible");
        //possibleWordsDisplay.setBounds(240, 0, 200, 200);

        UI.add(unscramblee);
        UI.add(submit);
        UI.add(possibleWordsDisplay);

        JScrollPane scrollPane = new JScrollPane(UI);
        f.getContentPane().add(scrollPane); //uses borderlayout by default 
        f.pack();
        f.setVisible(true); //make frame visible after construction is completed 
    }

    public static void main(String[] args) {
        new Application();
    }
}

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¹ 发布问题或答案时始终要考虑问题

Answer 2

创建GUI时，请考虑按照以下设计开始：

private JFrame frame;
private JPanel contentPane;

public static void main(String[] args) {
    GUI gui = new GUI();
    gui.start();

}

private void start() {
    frame = new JFrame("test");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    makeContent();

    frame.setSize(500, 130);
    frame.setVisible(true);

}

private void makeContent() {
    contentPane = (JPanel) frame.getContentPane();
    makePanel();

}

private void makePanel() {
    JPanel ui = new JPanel();
    ui.setLayout(new BoxLayout(ui, BoxLayout.Y_AXIS));

    JLabel possibleWordsDisplay = new JLabel("possibleWordsDisplay - this is a display for words that are possible"); 
    ui.add(possibleWordsDisplay);

    JTextField unscramblee = new JTextField();
    JScrollPane scroll = new JScrollPane(unscramblee);
    scroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    ui.add(scroll);

    JButton submit = new JButton("Submit");
    ui.add(submit);

    contentPane.add(ui, BorderLayout.CENTER);

}