Java 图形用户界面正在卡住

Question

为什么当我单击“输入”执行我的程序时，我的应用程序卡住了？

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JOptionPane;
import java.io.*;
import java.net.*;

public class KnockKnockUI{

      private Socket kkSocket = null;
      private PrintWriter out = null;
      private BufferedReader in = null;
      JTextArea clientArea;
      JTextArea serverArea;
    public KnockKnockUI(){

        establishConnection();
        initComponents();

    }

    public void initComponents(){

        JFrame frame = new JFrame("Chat");
        frame.setVisible(true);
        frame.setSize(320,189);
        frame.getContentPane().setLayout(null);

        serverArea = new JTextArea();
        serverArea.setLineWrap(true);
        serverArea.setBounds(10, 11, 284, 45);
        frame.getContentPane().add(serverArea);

        clientArea = new JTextArea();
        clientArea.setBounds(10, 67, 284, 46);
        frame.getContentPane().add(clientArea);

        JButton btnEnter = new JButton("Enter");
        btnEnter.setBounds(96, 124, 89, 23);
        frame.getContentPane().add(btnEnter);

        btnEnter.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try{
                    in.readLine();
                }catch(Exception e){

                }
                String fromUser = clientArea.getText();
                try {
                    fromUser = in.readLine();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                serverArea.setText(fromUser);
            }
        });

    }

    public void establishConnection(){

         //Establishes Connection
         try {
            kkSocket = new Socket("localhost", 4444);
            //
            out = new PrintWriter(kkSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: taranis.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: taranis.");
            System.exit(1);
        }

    }
    public static void main(String[] args){
        KnockKnockUI ui = new KnockKnockUI();
    }
}

这是一个使用 Java 的简单聊天客户端，还有其他我没有包含的类。像服务器类和协议(protocol)类

Answer 1

当您按下回车键时，将执行以下操作:

try {
    in.readLine();
} catch (Exception e) {
}

String fromUser = clientArea.getText();

try {
    fromUser = in.readLine();
} catch (IOException e) {
    e.printStackTrace();
}

serverArea.setText(fromUser);

这段代码正在 Event Dispatch Thread 上执行，它处理所有 Swing 事件。您对 in.readLine() 的调用将阻塞，直到从您的 Socket 获得一行输入，导致未处理的事件备份，从而导致您的程序停止响应。如果您想执行耗时的任务，请查看 SwingWorker (SwingWorker tutorial)。

旁注:捕获 Exception 而不打印其堆栈跟踪几乎总是一个坏主意。如果不是不可能的话，它会使您的代码问题更难发现。