带有GUI的简单Java程序，我的错误是什么？

Question

我有下面的代码（java）

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

    public class DirectoryIndexer extends JFrame implements ActionListener, MouseListener {

            JPanel OutputPane001 = new JPanel();
            JTextArea OutputTextArea001 = new JTextArea();

            JPanel zeButtonPane = new JPanel();
            JButton zeButton = new JButton("Index This Mess!");
            zeButton.addActionListener(this);

            JPanel InputPane001 = new JPanel();
            JTextField InputTextField001 = new JTextField();

            String[] DirList;
            String DirListConcat = "";


            public DirectoryIndexer() {
                super();
                setSize(750, 550);
                setTitle("920's Second Attempt At A Java Program With A GUI");
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                BorderLayout OutputPaneLayout = new BorderLayout();
                OutputPane001.setLayout(OutputPaneLayout);
                OutputTextArea001.setSize(550,435);
                OutputPane001.add(OutputTextArea001);
                OutputPane001.setSize(600,485);
                add(OutputPane001, BorderLayout.WEST);

                BorderLayout zeButtonPaneLayout = new BorderLayout();
                zeButtonPane.setLayout(zeButtonPaneLayout);
                zeButtonPane.add(zeButton);
                zeButtonPane.setSize(120,485);
                add(zeButtonPane, BorderLayout.EAST);

                BorderLayout InputPaneLayout = new BorderLayout();
                InputPane001.setLayout(InputPaneLayout);
                InputPane001.add(InputTextField001);
                InputPane001.setSize(720,20);
                add(InputPane001, BorderLayout.SOUTH);

                setVisible(true);
            }

            public void actionPerformed(ActionEvent event) {
                super();
                string DirToIndex = InputTextField001.getText();
                String files;
                File folder = new File(DirToIndex);
                File[] listOfFiles = folder.listFiles(); 

                for (int i = 0; i < listOfFiles.length; i++) 
                {        
                    if (listOfFiles[i].isFile()) 
                    {
                        files = listOfFiles[i].getName();
                        DirList[i] = files;
                        DirListConcat = DirListConcat + files;
                    }
                }

                OutputTextArea001.setText(DirListConcat);           

            }

            public static void main(String[] arguments) {
                DirectoryIndexer MainFrame = new DirectoryIndexer();
            }


    }

抱歉，如果显示不正确，当我尝试发布代码时，stackoverflow会出现故障...但是无论如何...

我是Java的初学者，尝试生成一个程序，该程序采用userinput“路径”，让用户按下按钮，然后转过身并对该目录建立索引，然后将输出打印到此textarea。

我收到以下错误：

    cmd /c cd "C:\Users\Charles\custom_java_dir\charles\GUI2" && "javac" "DirectoryIndexer.java"
    Process started >>>
    DirectoryIndexer.java:13: error: <identifier> expected
            zeButton.addActionListener(this);
                                      ^
    DirectoryIndexer.java:13: error: illegal start of type
            zeButton.addActionListener(this);
                                       ^
    2 errors
    <<< Process finished. (Exit code 1)
    cmd /c java DirectoryIndexer
    Process started >>>
    <<< Process finished. (Exit code 0)
    ================ READY ================

Answer 1

您正在尝试在方法之外发出Java语句。 您可以在方法之外声明变量，但不能在语句之外声明变量。

Answer 2

zeButton.addActionListener(this); 在DirectoryIndexer类的变量声明中，这是不正确的。 您只能从方法内部调用方法。

Answer 3

这种声明不能在方法之外： zeButton.addActionListener(this);

尝试将其移至构造函数。