[英]cannot instantiate type actionlistener?
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);
}
}
我得到這個錯誤無法實例化類型actionlistener。 代碼行是:
yourInputField.addActionListener(new ActionListener());
class MyActionListener implements ActionListener {
public void actionPerformed(ActionEvent evt) {
JTextField textfield = (JTextField)evt.getSource();
process(textfield.getText());
}
}
我正在嘗試創建一個JTextField來接收來自用戶的輸入。 仍然不成功。 什么導致錯誤?
如果您嘗試使用匿名內部類,它應該看起來像這樣:
yourInputField.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent arg0) {
JTextField textfield = (JTextField)evt.getSource();
process(textfield.getText());
}
});
但是如果你想使用嵌套類,它看起來像這樣:
yourInputField.addActionListener(new MyActionListener());
然后在聲明嵌套類的方法之外的某個地方:
private class MyActionListener implements ActionListener{
@Override
public void actionPerformed(ActionEvent e) {
TextField textfield = (JTextField)evt.getSource();
process(textfield.getText());
}
}
ActionListener是一個接口而不是類,您無法實例化接口。
更換:
yourInputField.addActionListener(new ActionListener());
有:
yourInputField.addActionListener(new MyActionListener());
ActionListener是一個接口,您無法實例化new ActionListener();
我認為在你的情況下你想要
yourInputField.addActionListener(new MyActionListener());
首先,您需要通過將以下行放在類的頂部來導入ActionListener和ActionEvent:
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
接下來,將MyActionListener內部類移動到構造函數之外的其他位置 - 在主要方法之后,在類的底部(不在main方法內部),這是一個好地方。
最后,將'new ActionListener()'替換為以下行中的'new MyActionListener()':
yourInputField.addActionListener(new ActionListener());
它將成為:
yourInputField.addActionListener(new MyActionListener());
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