如何使用java中的其他类公共类中定义的变量？ [英] How to use variables defined in a public class in other classes in java?

问题描述

我需要制作一个获取用户输入的Java GUI，并将其存储在文本文件中。然而，这个写作必须在一个Actionlistener类中完成（例如，用户点击按钮并创建并存储文本文件）。这意味着我必须在一个类（公共类）中定义一个变量，并在另一个类中定义一个变量（定义Actionlistener的变量）。

我该怎么做？是全局变量的唯一方法吗？

在我的代码中，我首先定义textfield为JTextField，然后我希望它被读取（如文本）和存储在'text.txt'）。

  import javax.swing。*; 
 // ... 
 import java.io.BufferedWriter; 
 
 public class Runcommand33 
 {
 public static void main（String [] args）
 {
 final JFrame frame = new JFrame（Change Backlight ）; 
 // ... 
 //定义框架，面板，按钮和位置
 JTextField textfield = new JTextField（）; textfield.setBounds（35,20,160,30）; 
 panel.add（textfield）; 
 frame.setVisible（true）; 
 button.addActionListener（new ButtonHandler（））; 
 
 
 $ b class ButtonHandler实现ActionListener {
 public void actionPerformed（ActionEvent event）{
 String text = textfield.getText（）; 
 textfield.setText（）; 
 new BufferedWriter（new FileWriter（text.txt））。write（text）.newLine（）。close（）; 
 
 //之后需要'text'来运行一个命令
 
 
 code $ pre 
 
 
当我编译时，我得到
 
 
  Runcommand33.java:45：error：can not find symbol 
 String text = textfield.getText（）; 
 $ 
符号：变量textfield 
位置：class ButtonHandler 
  
没有行 String text = 新的BufferedWriter 代码编译。
 
 
 
请注意，我已经尝试了这个建议
 在其他类中获取变量 
和
 如何在另一个类的函数中访问一个类的变量？ 
但是他们没有工作。
 
 
 
有什么建议吗？我们从设计的角度来看这个： ButtonHandler 听起来有点过于简单通用的。点击处理按钮的方式是什么？嗯，它将文本字段的内容保存到一个文件，所以它应该被称为TextFieldSaver（或最好不要跛脚）。
 
 
现在，一个TextFieldSaver需要有一个文本字段来保存，是吗？因此，添加一个成员变量来保存文本字段，并通过构造函数传递在主类中创建的文本字段： 
 
 
  button .addActionListener（new TextFieldSaver（textfield））; 
 
 ... 
 
 class TextFieldSaver实现ActionListener {
 JTextField textfield; 
 public TextFieldSaver（JTextField toBeSaved）{
 textfield = toBeSaved; 
 
 public void actionPerformed（ActionEvent event）{
 String text = textfield.getText（）; 
 textfield.setText（）; 
 new BufferedWriter（new FileWriter（text.txt））。write（text）.newLine（）。close（）; 
 
 
 
 
 $ b 
这不是唯一的办法，也不一定是最好的方法，但我希望它显示如何使用专有名称有时显示出路。
 
A layman's question on the definition and use of variables:

I need to make a Java GUI that gets user's input and stores it within a text file. However this writing has to be done inside an Actionlistener class (ie, user is clicking the button and text file is created and stored). This means that I have to define a variable in one class (public class) and use it in another (the one that defines the Actionlistener).

How can I do this? Are global variables the only way?

In my code I first define 'textfield' as JTextField and then I want it to be read (as 'text') and stored (in 'text.txt').
import javax.swing.*;
//...
import java.io.BufferedWriter;

public class Runcommand33
{
  public static void main(String[] args)
  {
final JFrame frame = new JFrame("Change Backlight");
   // ...
   // define frames, panels, buttons and positions
    JTextField textfield = new JTextField();textfield.setBounds(35,20,160,30);
    panel.add(textfield);
    frame.setVisible(true);
    button.addActionListener(new ButtonHandler());
  }
}

    class ButtonHandler implements ActionListener{
    public void actionPerformed(ActionEvent event){
    String text = textfield.getText();
        textfield.setText("");
        new BufferedWriter(new FileWriter("text.txt")).write(text).newLine().close();

    // Afterwards 'text' is needed to run a command
              }
            }
When I compile I get
Runcommand33.java:45: error: cannot find symbol
                String text = textfield.getText();
                              ^
  symbol:   variable textfield
  location: class ButtonHandler
Without lines String text =  to new BufferedWriter the code compiles.

Note that I have tried the suggestions of this
Get variable in other classes
and this
How do I access a variable of one class in the function of another class?
but they didn't work.

Any suggestions?
解决方案
Let's look at this from a design perspective: ButtonHandler sounds a little too generic. In what way is the button click "handled"? Ah, it saves the contents of the text field to a file, so it should be called "TextFieldSaver" (or preferably something less lame).

Now, a TextFieldSaver needs to have a text field to save, yes? So add a member variable to hold the text field, and pass the text field created in the main class through a constructor:
    button.addActionListener(new TextFieldSaver(textfield));

....

class TextFieldSaver implements ActionListener {
    JTextField textfield;
    public TextFieldSaver(JTextField toBeSaved) {
        textfield = toBeSaved;
    }
    public void actionPerformed(ActionEvent event) {
        String text = textfield.getText();
        textfield.setText("");
        new BufferedWriter(new FileWriter("text.txt")).write(text).newLine().close();
    }
}
This isn't the only way to do it, nor necessarily the best way, but I hope it shows how using proper names sometimes shows a way out.

                        
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