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I see several issues with your code, but the main one being that you appear to be trying to add the JTextArea to the GUI two or maybe even three times:

我看到你的代码有几个问题,但主要的是你似乎试图将JTextArea添加到GUI两次甚至三次:

You first add it to the JScrollPane:

首先将其添加到JScrollPane:

private JScrollPane scrollPane = new JScrollPane(textArea, 
          JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
        JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

And add that JScrollPane to the GUI

并将JScrollPane添加到GUI

getContentPane().add(scrollPane);

But then immediately after, you appear to add just the JTextArea without its JScrollPane to the GUI:

但是之后不久,您似乎只将JTextArea添加到GUI而没有JScrollPane:

getContentPane().add(textArea);

Understand that you can add a component to the GUI only once. If you try to add it a 2nd time, it is removed from the prior container, leaving it empty. Not only that, by adding a component to a BorderLayout-using container in this way (the content pane), you replace the JScrollPane from the GUI completely.

了解您只能将组件添加到GUI一次。如果您尝试第二次添加它,它将从之前的容器中删除,将其留空。不仅如此,通过以这种方式(内容窗格)向BorderLayout使用容器添加组件,您可以完全从GUI替换JScrollPane。

You also might be adding the JTextArea to the GUI a third time when you add it to your LineNumberingTextArea constructor:

当您将JTextArea添加到LineNumberingTextArea构造函数时,也可能第三次将JTextArea添加到GUI:

final LineNumberingTextArea lineNTA = new LineNumberingTextArea(textArea);

and then add the LineNumberingTextArea object to the GUI:

然后将LineNumberingTextArea对象添加到GUI:

getContentPane().add(lineNTA,BorderLayout.WEST);

We don't know what goes on inside of your LineNumberingTextArea, but if you're adding the JTextArea to the LineNumberingTextArea instance, and then as above are adding your LineNumberingTextArea instance to the GUI, again that makes three times that you're trying to add the JTextArea to a container, which is two times too many.

我们不知道你的LineNumberingTextArea里面发生了什么,但是如果你要将JTextArea添加到LineNumberingTextArea实例,然后如上所述将你的LineNumberingTextArea实例添加到GUI,那么再次使你想要尝试三次将JTextArea添加到容器中,这是两倍太多。

Again, you can only add a component to the GUI once.

同样,您只能将一个组件添加到GUI一次。

Other side issues:

其他方面的问题:

• You are trying to set the sizes or preferred sizes of components, something you will want to avoid. Rather let the components and the layout managers size themselves to their best sizes.

您正在尝试设置组件的大小或首选大小,这是您希望避免的。相反,让组件和布局管理器将自己调整到最佳尺寸。

• You're setting your JTextArea rows and columns properties to too small values of 0,0: private JTextArea textArea = new JTextArea(0,0);. Much better to use this constructor as a more robust way of having the JTextArea size itself appropriately by passing in more reasonable values.

您将JTextArea行和列属性设置为太小的值0,0:private JTextArea textArea = new JTextArea(0,0);.使用这个构造函数更好的方法是通过传递更合理的值来更好地使JTextArea大小本身。

• You're also adding components to a BorderLayout-using container, the contentPane, in a default way, multiple times, which means that you're displacing any component added previously with the newly added components, something that is likely further confusing you.

您还要以默认方式多次向BorderLayout使用容器(contentPane)添加组件,这意味着您将使用新添加的组件替换先前添加的任何组件,这可能会让您更加困惑。

• You're creating two JFrames -- why? One is the when you create an instance of MyTextEditor, since it extends from JFrame. This is the JFrame that gets all components. The other is a private field:

你正在创建两个JFrame - 为什么?一个是你创建MyTextEditor实例的时候,因为它是从JFrame扩展的。这是获取所有组件的JFrame。另一个是私人领域:

private JFrame frame = new JFrame();

and you call methods on it:

你在上面调用方法:

frame.setTitle("Zenith");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

but never add anything to it or display it. Since this will serve no purpose other than to confuse, you should get rid of one JFrame or the other. Again this suggests that you might want to start over and start cleaner and with a well-defined purpose.

但永远不要添加任何东西或显示它。因为除了混淆之外没有任何其他目的,你应该摆脱一个JFrame或另一个。这再次暗示您可能希望重新开始并以明确的目的开始清洁。

For example, a simple GUI demo:

例如,一个简单的GUI演示:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;

import javax.swing.*;

public class SimpleScrollPaneGui extends JPanel {
    private static final int ROWS = 25;
    private static final int COLUMNS = 60;
    private static final Color TA_BACKGRND = Color.BLACK;
    private static final Color TA_FOREGRND = Color.GREEN;
    private static final Color TA_CARET_COLOR = Color.WHITE;
    private static final Font TA_FONT = new Font("Consolas", Font.BOLD, 14);

    // first off size your JTextArea by setting visible rows and columns
    private JTextArea textArea = new JTextArea(ROWS, COLUMNS); 

    public SimpleScrollPaneGui() {
        // set the text area properties
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        textArea.setBackground(TA_BACKGRND);
        textArea.setForeground(TA_FOREGRND);
        textArea.setCaretColor(TA_CARET_COLOR);
        textArea.setFont(TA_FONT);

        // create jscrollpane, passing in jtextarea into its viewport:
        JScrollPane scrollPane = new JScrollPane(textArea);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        setLayout(new BorderLayout());

        // add **just the jscrollpane to the GUI
        add(scrollPane);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            createAndShowGui();
        });
    }

    private static void createAndShowGui() {
        SimpleScrollPaneGui mainPanel = new SimpleScrollPaneGui();
        JFrame frame = new JFrame("Simple ScrollPane GUI");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
}