如何从内部类的 try 块中获取字符串答案

【问题标题】：How to get a string from a try block in an inner class如何从内部类的 try 块中获取字符串
【发布时间】：2017-04-27 10:18:43
【问题描述】：

我正在尝试将标签设置为读者收到的字符串，在实现 ActionListener 的内部类中。但我得到一个未知的符号错误。如何在内部类中引用该变量

import java.io.*;
import java.net.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
public class DailyAdviceClient {
  JLabel label;
  JButton button;
  JFrame frame;
  JPanel mainPanel;

  public void gui() {
    frame = new JFrame("Daily Advice Client");
    button = new JButton("Get Advice");
    label = new JLabel("Text");
    mainPanel = new JPanel();
    mainPanel.add(button);
    mainPanel.add(label);

    button.addActionListener(new AdviceListener());
    frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

    frame.setSize(300,400);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

  }
  public void go() {
    try {
      Socket s = new Socket("127.0.0.1", 4242);

      InputStreamReader streamReader = new InputStreamReader(s.getInputStream());
      BufferedReader reader = new BufferedReader(streamReader);

      String advice = reader.readLine();
      System.out.println("Today you should: " + advice);
      reader.close();
    }
    catch (IOException e) {
      System.out.println("Hayt tumhari ki");
      System.out.print("I didn't think we would get to this stage. Please ");
      System.out.println("kill the developer. \n");
      e.printStackTrace();
    }
  }

  public static void main(String[] args) {
    DailyAdviceClient client = new DailyAdviceClient();
    client.go();
    client.gui();
  }

  public class AdviceListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      label.setText(advice);
    }
  }
}

【问题讨论】：

字符串需要在try块前声明
了解 Java 变量的范围。它只存在于它被声明的范围（和“子范围”）
您未能在事件调度线程 (EDT) 上启动 GUI。您不能像这里那样在主线程上安全地运行 GUI。

标签： java swing inner-classes

【解决方案1】：

这可以通过应用 MVC 模式轻松解决：

你只有一个Controller和一个View，但是你缺少一个共同的Model，它们都可以工作。

最简单的实现是将局部变量advice 提升为对象成员变量，作为模型：

public class DailyAdviceClient {
  private String advice;
  // ...
  advice = reader.readLine();
  // ...

并将AdviceListener 类转换为匿名内部类 作为lambda：

button.addActionListener(ae->label.setText(advice));

【讨论】：

【解决方案2】：

将您的字符串 advice 声明为实例/字段变量：

import java.io.*;
import java.net.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
public class DailyAdviceClient {
  JLabel label;
  JButton button;
  JFrame frame;
  JPanel mainPanel;
  String advice;

  public void gui() {
    frame = new JFrame("Daily Advice Client");
    button = new JButton("Get Advice");
    label = new JLabel("Text");
    mainPanel = new JPanel();
    mainPanel.add(button);
    mainPanel.add(label);

    button.addActionListener(new AdviceListener());
    frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

    frame.setSize(300,400);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

  }
  public void go() {
    try {
      Socket s = new Socket("127.0.0.1", 4242);

      InputStreamReader streamReader = new InputStreamReader(s.getInputStream());
      BufferedReader reader = new BufferedReader(streamReader);

      advice = reader.readLine();
      System.out.println("Today you should: " + advice);
      reader.close();
    }
    catch (IOException e) {
      System.out.println("Hayt tumhari ki");
      System.out.print("I didn't think we would get to this stage. Please ");
      System.out.println("kill the developer. \n");
      e.printStackTrace();
    }
  }

  public static void main(String[] args) {
    DailyAdviceClient client = new DailyAdviceClient();
    client.go();
    client.gui();
  }

  public class AdviceListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      label.setText(advice);
    }
  }
}

【讨论】：