Java 无法使此方法工作

在添加actionPerformed方法后，我无法使此小程序正常工作。。。有什么建议吗

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class JGreet3 extends JApplet implements ActionListener
{

   public void init()
   {
      Container con = getContentPane();
      JLabel greeting = new JLabel("Greetings!");
      Font bigFont = new Font("Times Roman", Font.ITALIC, 24);
      greeting.setFont(bigFont);

      JLabel firstLabel = new JLabel("Please enter your first name:");
      JLabel lastLabel = new JLabel("Please enter your last name:");
      JTextField firstField = new JTextField("", 10);
      JTextField lastField = new JTextField("", 10);
      JButton viewButton = new JButton("View Greeting");

      viewButton.addActionListener(this);

      FlowLayout flow = new FlowLayout();
      con.setLayout(flow);
      con.add(firstLabel);
      con.add(firstField);
      con.add(lastLabel);
      con.add(lastField);
      con.add(viewButton);

      firstField.requestFocus();

      con.add(greeting);

   }

   public void actionPerformed(ActionEvent thisEvent)
   {
      String firstName = firstField.getText();
      String lastName = lastField.getText();
      greeting.setText("How are you, " + firstName + " " + lastName + "?");
   }

}

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我得到的错误是找不到firstField.getText、lastField.getText和greeting.setText的符号

您需要使它们成为成员变量。成员变量可供所有类方法访问：

public class JGreet3 extends JApplet implements ActionListener {

    JLabel greeting;
    JTextField firstField;
    JTextField lastField;

    public void init() {
        greeting = new JLabel("Greetings!");
        firstField = new JTextField("", 10);
        lastField = new JTextField("", 10);

        ....
    }

    ...

    public void actionPerformed(ActionEvent thisEvent) {
        // Now your textFields are accessible
        String firstName = firstField.getText();
        String lastName = lastField.getText();
        greeting.setText("How are you, " + firstName + " " + lastName + "?");
    }

}

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将JLabel firstLabel移出方法，使其成为一个字段，您可以从另一个方法引用它