java - 如何将文档监听器添加到 JScrollPane 内的 JTextArea？

Question

我正在尝试向 JTextArea 添加一个文档监听器，这样当用户按下回车键时，它将读取最后一行/自新行以来的字符。

我尝试了以下代码，但 Eclipse 不喜欢 display.getDocument().addDocumentListener(new AL());。它说

No enclosing instance of type ScrollingTextArea is accessible. Must qualify the allocation with an enclosing instance of type ScrollingTextArea (e.g. x.new A() where x is an instance of ScrollingTextArea).

如何向 JTextArea 添加 Action 监听器？

代码:

package guis;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;
import javax.swing.border.EtchedBorder;
import javax.swing.border.TitledBorder;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class ScrollingTextArea {

    public static void main ( String[] args )
    {
        JPanel middlePanel = new JPanel ();
        middlePanel.setBorder(new TitledBorder(new EtchedBorder (), "Display Area" ) );

        // create the middle panel components

        JTextArea display = new JTextArea(16,58 );
        JScrollPane scroll = new JScrollPane(display);

        display.getDocument().addDocumentListener(new AL());
        scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

        //Add Textarea in to middle panel
        middlePanel.add(scroll);

        JFrame frame = new JFrame();
        frame.add( middlePanel );
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    public class AL implements DocumentListener {


        @Override
        public void insertUpdate(DocumentEvent e) {
            // TODO Auto-generated method stub

        }

        @Override
        public void removeUpdate(DocumentEvent e) {
            // TODO Auto-generated method stub

        }

        @Override
        public void changedUpdate(DocumentEvent e) {
            // TODO Auto-generated method stub

        }
    }
}

Answer 1

nested类 AL 需要是静态的。除非出于某种原因需要导出该类，否则它应该是 private。

private static class AL implements DocumentListener {…}