无法为静态 final 变量赋值。

huangapple
go评论95阅读模式
英文:

Cannot assign value to static final variable

问题

我正在尝试为我的游戏创建一个配置文件系统，我希望用户提供的配置信息被存储为Config类中的public static final变量，以便游戏中的所有类都可以安全地访问配置数据。以下是我迄今为止编写的代码：

  1. import java.io.*;
  2. import java.util.Scanner;
  4. public class Config {
  6.     private static final int n = 4;
  7.     private static String[] values = new String[n];
  8.     public static final String MUSIC_PATH;
  9.     public static final String SAVE_PATH;
  10.     public static final int WIDTH;
  11.     public static final int HEIGHT;
  13.     public static void ini() throws FileNotFoundException, IOException  {
  14.         File f = new File("config.txt");
  15.         Scanner lineScanner = new Scanner(f);
  16.         for (int i = 0; i < n; i++) {
  17.             Scanner valueGetter = new Scanner(lineScanner.nextLine());
  18.             valueGetter.useDelimiter(": ");
  19.             valueGetter.next();
  20.             values[i] = valueGetter.next();
  21.         }
  22.         WIDTH = Integer.parseInt(values[0]);
  23.         HEIGHT = Integer.parseInt(values[1]);
  24.         SAVE_PATH = values[2];
  25.         MUSIC_PATH = values[3];
  26.     }
  27. }

当我尝试编译代码时，我收到“无法为final变量分配值”的错误消息。如果我删除了final关键字，代码可以正常工作，但我宁愿不这样做，因为它们是公共变量，我不希望它们被误操作。

我认为在我目前的方法中，没有轻松的方法来解决这个问题，但如果有人可以查看这个问题并告诉我如何实现我想要的目标，我将不胜感激 无法为静态 final 变量赋值。

英文:

I am trying to create a config file system for my game, and I want the config info from the user to be stored as public static final variables in a Config class, so all classes within the game can access the config data safely. Here is the code I have written so far:

  1. import java.io.*;
  2. import java.util.Scanner;
  4. public class Config {
  6. 	private static final int n = 4;
  7. 	private static String[] values = new String[n];
  8. 	public static final String MUSIC_PATH;
  9. 	public static final String SAVE_PATH;
  10. 	public static final int WIDTH;
  11. 	public static final int HEIGHT;
  13. 	public static void ini() throws FileNotFoundException, IOException  {
  14. 		File f = new File(&quot;config.txt&quot;);
  15. 		Scanner lineScanner = new Scanner(f);
  16. 		for (int i = 0; i&lt;n; i++) {
  17. 			Scanner valueGetter = new Scanner(lineScanner.nextLine());
  18. 			valueGetter.useDelimiter(&quot;: &quot;);
  19. 			valueGetter.next();
  20. 			values[i] = valueGetter.next();
  21. 		}
  22. 		WIDTH = Integer.parseInt(values[0]);
  23. 		HEIGHT = Integer.parseInt(values[1]);
  24. 		SAVE_PATH = values[2];
  25. 		MUSIC_PATH = values[3];
  27. 	}
  29. }

When I try to compile the code I get the error "cannot assign a value to final variable". I am able to get the code working if I remove the final, however I would prefer not to do this as they are public variables I don't want them getting messed up or anything.

I figure there is no easy way to get around this issue with the way I have currently done it, but if anyone can look at this and tell me a way to accomplish what I want then I would appreciate 无法为静态 final 变量赋值。

答案1

得分: 2

您可以在静态块中初始化static final字段。

因此，请删除ini方法，并替换为：

  1. static {
  2.    // 曾经在ini方法中的代码在这里...
  3. }

请注意，静态块无法抛出已检查异常，因此在创建Scanner时需要处理异常：

  1. try {
  2.     Scanner lineScanner = new Scanner(f);
  3.     // 其余的代码...
  4. } catch (FileNotFoundException e) {
  5.     // 在这里处理异常...
  6.     // 可能将字段设置为某些默认值
  7. }

我还建议将字段设置为私有，并为它们添加getter方法。此外，考虑根本不将它们设置为static，而是使用公共setter设置静态currentConfig字段。它看起来可能像这样：

  1. class Config {
  3.     private final int n = 4;
  4.     private String[] values = new String[n];
  5.     private final String MUSIC_PATH;
  6.     private final String SAVE_PATH;
  7.     private final int WIDTH;
  8.     private final int HEIGHT;
  10.     // 获取私有字段的getter方法...
  12.     private static Config currentConfig;
  14.     public static Config getCurrentConfig() {
  15.         return currentConfig;
  16.     }
  18.     public static void setCurrentConfig(Config currentConfig) {
  19.         Config.currentConfig = currentConfig;
  20.     }
  22.     private Config(File configFile) throws FileNotFoundException {
  23.         // 使用configFile的内容初始化final字段...
  24.     }
  25. }

在程序开始时，您可以这样做：

  1. Config.setCurrentConfig(new Config(new File("config.txt")));
英文:

You can initialise static final fields in a static block.

So remove the ini method, and replace it with:

  1. static {
  2.    // the code that used to be in the ini method here...
  3. }

Note that a static block cannot throw checked exceptions, so you need to handle the exception when creating a Scanner:

  1. try {
  2.     Scanner lineScanner = new Scanner(f);
  3.     // the rest of your code...
  4. } catch (FileNotFoundException e) {
  5.     // handle the exception here...
  6.     // perhaps set the fields to something default
  7. }

I would also recommend making the fields private add getters for them. Also consider not having them static at all, and instead have a static currentConfig field that can be set with a public setter. It would look something like this:

  1. class Config {
  3.     private final int n = 4;
  4.     private String[] values = new String[n];
  5.     private final String MUSIC_PATH;
  6.     private final String SAVE_PATH;
  7.     private final int WIDTH;
  8.     private final int HEIGHT;
  10.     // getters for the private fields...
  12.     private static Config currentConfig;
  14.     public static Config getCurrentConfig() {
  15.         return currentConfig;
  16.     }
  18.     public static void setCurrentConfig(Config currentConfig) {
  19.         Config.currentConfig = currentConfig;
  20.     }
  22.     private Config(File configFile) throws FileNotFoundException {
  23.         // initialise the final fields using the configFile&#39;s contents...
  24.     }
  25. }

At the start of your program you'd then do something like this:

  1. Config.setCurrentConfig(new Config(new File(&quot;config.txt&quot;)));

huangapple
  • 本文由 发表于 2023年6月13日 15:43:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/76462687.html
  • java
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定