无法实例化类型actionlistener？

Question

import org.jsoup.Jsoup;

@SuppressWarnings("unused")

public class SimpleWebCrawler extends JFrame implements ActionListener {

    JTextField yourInputField = new JTextField(20);
    static JTextArea _resultArea = new JTextArea(200, 200);
    JScrollPane scrollingArea = new JScrollPane(_resultArea);
    private final static String newline = "\n";
    JButton jButton = new JButton("Send Text");

    public SimpleWebCrawler() throws MalformedURLException  {

        yourInputField.addActionListener(new ActionListener());

        class MyActionListener implements ActionListener {
            public void actionPerformed(ActionEvent evt) {
                JTextField textfield = (JTextField)evt.getSource();
                process(textfield.getText());
            }
        }

        String word2 = yourInputField.getText();

        _resultArea.setEditable(false);

        try {
            URL my_url = new URL("http://" + word2 + "/");
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    my_url.openStream()));
            String strTemp = "";
            while (null != (strTemp = br.readLine())) {
                _resultArea.append(strTemp + newline);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        _resultArea.append("\n");
        _resultArea.append("\n");
        _resultArea.append("\n");


        String url = "http://" + word2 + "/";
        print("Fetching %s...", url);

        try{
        Document doc = Jsoup.connect(url).get();
        Elements links = doc.select("a[href]");

        System.out.println("\n");

        BufferedWriter bw = new BufferedWriter(new 
                FileWriter("C:\\Users\\user\\fypworkspace\\FYP\\Link\\abc.txt"));
        _resultArea.append("\n");
        for (Element link : links) {
            print("  %s  ", link.attr("abs:href"), trim(link.text(), 35));

            bw.write(link.attr("abs:href"));
            bw.write(System.getProperty("line.separator"));
        }
        bw.flush();
        bw.close();
        } catch (IOException e1) {

        }
        JPanel content = new JPanel();
        content.setLayout(new BorderLayout());
        content.add(scrollingArea, BorderLayout.CENTER);
        content.add(yourInputField,BorderLayout.SOUTH);
        content.add(jButton, BorderLayout.EAST);

        this.setContentPane(content);
        this.setTitle("Crawled Links");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();


        }

        private static void print(String msg, Object... args) {

            _resultArea.append(String.format(msg, args) +newline);
        }

        private static String trim(String s, int width) {
            if (s.length() > width)
                return s.substring(0, width - 1) + ".";
            else
                return s;
        }

        //.. Get the content pane, set layout, add to center




    public static void main(String[] args) throws IOException {

        JFrame win = new SimpleWebCrawler();
        win.setVisible(true);

    }
}

我收到此错误无法实例化类型动作侦听器。代码行是：

yourInputField.addActionListener(new ActionListener());

        class MyActionListener implements ActionListener {
            public void actionPerformed(ActionEvent evt) {
                JTextField textfield = (JTextField)evt.getSource();
                process(textfield.getText());
            }
        }

我正在尝试创建一个 JTextField 来接收用户的输入。还是没有成功。是什么导致了错误？

Answer 1

如果您尝试使用匿名内部类，它应该如下所示：

yourInputField.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent arg0) {
             JTextField textfield = (JTextField)evt.getSource();
                         process(textfield.getText());
        }
    });

但如果您想使用嵌套类，它可以如下所示：

yourInputField.addActionListener(new MyActionListener());

然后在方法之外的某个地方声明嵌套类：

      private class MyActionListener implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            TextField textfield = (JTextField)evt.getSource();
                             process(textfield.getText());
        }
    }

Answer 2

ActionListener 是一个接口而不是类，并且您不能实例化接口。

替换：

yourInputField.addActionListener(new ActionListener());

为：

yourInputField.addActionListener(new MyActionListener());

Answer 3

ActionListener 是一个接口，您无法实例化像 new ActionListener(); 这样的

接口，我认为在您的情况下您想要

yourInputField.addActionListener(new MyActionListener());

Answer 4

首先，您需要导入 ActionListener 和 ActionEvent，方法是将以下几行放在类的顶部：

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

接下来，将 MyActionListener 内部类移动到构造函数之外的其他位置 - 一个好的位置是在 main 方法之后，在类的底部（虽然不在 main 方法内）。

最后，将以下行中的“new ActionListener()”替换为“new MyActionListener()”：

yourInputField.addActionListener(new ActionListener());

它将变为：

yourInputField.addActionListener(new MyActionListener());