如何从不同的类访问变量[关闭]

Question

一旦用户输入了他的消息，我正在尝试从另一个类访问存储在“tf”中的值。
自从我使用 Java 以来已经有一段时间了，所以，我做这个项目只是为了好玩（不是我的代码，我只是根据教程编辑它）。
我尝试了很多东西，研究了很多与方法和对象有关的东西，我觉得我已经很接近了。我试图访问的值是在线的“tf”：

client.sendMessage(new ChatMessage(ChatMessage.MESSAGE, tf.getText()));
tf.setText("");
return;

我的目标只是在另一个类中打印来自“tf”的字符串。

public class ClientGUI extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;
    // will first hold "Username:", later on "Enter message"
    private JLabel label;
    // to hold the Username and later on the messages
    private JTextField tf;
    // to hold the server address an the port number
    private JTextField tfServer, tfPort;
    // to Logout and get the list of the users
    private JButton login, logout, whoIsIn;
    // for the chat room
    private JTextArea ta;
    // if it is for connection
    private boolean connected;
    // the Client object
    private Client client;
    // the default port number
    private int defaultPort;
    public String userMessage;
    private String defaultHost;
    // Constructor connection receiving a socket number
    ClientGUI(String host, int port) {

        super("Chat Client");
        defaultPort = port;
        defaultHost = host;

        // The NorthPanel with:
        JPanel northPanel = new JPanel(new GridLayout(3,1));
        // the server name and the port number
        JPanel serverAndPort = new JPanel(new GridLayout(1,5, 1, 3));
        // the two JTextField with default value for server address and port number
        tfServer = new JTextField(host);
        tfPort = new JTextField("" + port);
        tfPort.setHorizontalAlignment(SwingConstants.RIGHT);

        serverAndPort.add(new JLabel("Server Address:  "));
        serverAndPort.add(tfServer);
        serverAndPort.add(new JLabel("Port Number:  "));
        serverAndPort.add(tfPort);
        serverAndPort.add(new JLabel(""));
        // adds the Server an port field to the GUI
        northPanel.add(serverAndPort);

        // the Label and the TextField
        label = new JLabel("Enter your username below", SwingConstants.CENTER);
        northPanel.add(label);
        tf = new JTextField("Scooby Doo");
        tf.setBackground(Color.WHITE);
        northPanel.add(tf);
        add(northPanel, BorderLayout.NORTH);

        // The CenterPanel which is the chat room
        ta = new JTextArea("Welcome to the Chat room\n", 80, 80);
        JPanel centerPanel = new JPanel(new GridLayout(1,1));
        centerPanel.add(new JScrollPane(ta));
        ta.setEditable(false);
        add(centerPanel, BorderLayout.CENTER);

        // the 3 buttons
        login = new JButton("Login");
        login.addActionListener(this);
        logout = new JButton("Logout");
        logout.addActionListener(this);
        logout.setEnabled(false);       // you have to login before being able to logout
        whoIsIn = new JButton("Who is in");
        whoIsIn.addActionListener(this);
        whoIsIn.setEnabled(false);      // you have to login before being able to Who is in

        JPanel southPanel = new JPanel();
        southPanel.add(login);
        southPanel.add(logout);
        southPanel.add(whoIsIn);
        add(southPanel, BorderLayout.SOUTH);

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(600, 600);
        setVisible(true);
        tf.requestFocus();

    }


    // called by the Client to append text in the TextArea
    void append(String str) {
        ta.append(str);
        ta.setCaretPosition(ta.getText().length() - 1);
    }
    // called by the GUI is the connection failed
    // we reset our buttons, label, textfield
    void connectionFailed() {
        login.setEnabled(true);
        logout.setEnabled(false);
        whoIsIn.setEnabled(false);
        label.setText("Enter your username below");
        tf.setText("Anonymous");
        // reset port number and host name as a construction time
        tfPort.setText("" + defaultPort);
        tfServer.setText(defaultHost);
        // let the user change them
        tfServer.setEditable(false);
        tfPort.setEditable(false);
        // don't react to a <CR> after the username
        tf.removeActionListener(this);
        connected = false;
    }

    /*
    * Button or JTextField clicked
    */
    public void actionPerformed(ActionEvent e) {
        Object o = e.getSource();
        // if it is the Logout button
        if(o == logout) {
            client.sendMessage(new ChatMessage(ChatMessage.LOGOUT, ""));
            return;
        }
        // if it the who is in button
        if(o == whoIsIn) {
            client.sendMessage(new ChatMessage(ChatMessage.WHOISIN, ""));
            return;
        }

        // ok it is coming from the JTextField
        if(connected) {

            // just have to send the message
            client.sendMessage(new ChatMessage(ChatMessage.MESSAGE, tf.getText()));
            tf.setText("");
            return;
        }


        if(o == login) {
            // ok it is a connection request
            String username = tf.getText().trim();
            // empty username ignore it
            if(username.length() == 0)
            return;
            // empty serverAddress ignore it
            String server = tfServer.getText().trim();
            if(server.length() == 0)
            return;
            // empty or invalid port numer, ignore it
            String portNumber = tfPort.getText().trim();
            if(portNumber.length() == 0)
            return;
            int port = 0;
            try {
                port = Integer.parseInt(portNumber);
            }
            catch(Exception en) {
                return;   // nothing I can do if port number is not valid
            }

            // try creating a new Client with GUI
            client = new Client(server, port, username, this);
            // test if we can start the Client
            if(!client.start())
            return;
            tf.setText("");
            label.setText("Enter your message below");
            connected = true;

            // disable login button
            login.setEnabled(false);
            // enable the 2 buttons
            logout.setEnabled(true);
            whoIsIn.setEnabled(true);
            // disable the Server and Port JTextField
            tfServer.setEditable(false);
            tfPort.setEditable(false);
            // Action listener for when the user enter a message
            tf.addActionListener(this);
        }

    }


    // to start the whole thing the server
    public static void main(String[] args) {
        new ClientGUI("124.178.99.83", 25565);
    }

}

Answer 1

您必须通过构造函数通过引用传递对象。您可以传递整个 JFrame 并将您的 tf 公开 -

public static void main(String[] args){
    ClientGUI x = new ClientGUI("0.0.0.0", 1234);
    OtherClass y = new OtherClass(x);
}

public class otherClass {
     private ClientGUI x;
     public otherClass(ClientGUI x){
          this.x = x;
     }
     public void print(){
          System.out.println(x.tf.getText());
     }
}

或者您可以在创建其他类时传递 tf 值