如何从另一个Java类中动态访问静态变量？

Hey there! Let's work through this problem where you can access your DummyData static variables directly (like DummyData.Survey_1) but can't get their values using a dynamic string variable (like data).

Java is a statically typed language, so it doesn't natively support accessing fields by a runtime-generated string out of the box. But we've got two solid approaches to fix this:

1. Use Java Reflection API #

If you want to keep your existing DummyData class structure as-is, reflection lets you dynamically look up and access static fields at runtime. Here's how to implement it:

First, add a helper method to your DummyData class to handle the reflection logic:

import java.lang.reflect.Field;

public class DummyData {
    public static String Survey_1 = "Your Survey 1 content";
    public static String Survey_2 = "Your Survey 2 content";
    public static String Survey_3 = "Your Survey 3 content";

    // Helper method to fetch static field value dynamically
    public static String getDynamicSurveyValue(String fieldName) {
        try {
            // Get the public static field by name from DummyData class
            Field targetField = DummyData.class.getField(fieldName);
            // For static fields, pass null as the object instance parameter
            return (String) targetField.get(null);
        } catch (NoSuchFieldException e) {
            System.err.println("Field '" + fieldName + "' doesn't exist in DummyData");
            return null;
        } catch (IllegalAccessException e) {
            System.err.println("No permission to access field '" + fieldName + "'");
            return null;
        }
    }
}

How to use it: #

When you have your dynamic variable data (e.g., data = "Survey_1"), just call:

String surveyValue = DummyData.getDynamicSurveyValue(data);

Note: Reflection relies on exact field name matches (case-sensitive!), and only works with public fields (which your variables already are).

2. Use a Map for Storing Survey Data (Recommended) #

If you're open to adjusting your class structure, using a Map to store your survey values is cleaner, type-safe, and avoids the complexity of reflection. It's also easier to maintain if you add more survey variables later.

Here's the refactored DummyData class:

import java.util.HashMap;
import java.util.Map;

public class DummyData {
    // Store all survey values in a static Map
    private static final Map<String, String> SURVEY_MAP = new HashMap<>();

    // Initialize the Map in a static block
    static {
        SURVEY_MAP.put("Survey_1", "Your Survey 1 content");
        SURVEY_MAP.put("Survey_2", "Your Survey 2 content");
        SURVEY_MAP.put("Survey_3", "Your Survey 3 content");
    }

    // Optional: Keep your original static variables for backward compatibility
    public static String Survey_1 = SURVEY_MAP.get("Survey_1");
    public static String Survey_2 = SURVEY_MAP.get("Survey_2");
    public static String Survey_3 = SURVEY_MAP.get("Survey_3");

    // Helper method to fetch values dynamically
    public static String getDynamicSurveyValue(String key) {
        // Return null if key doesn't exist, or use getOrDefault for a default value
        return SURVEY_MAP.get(key);
        // Example with default value: return SURVEY_MAP.getOrDefault(key, "No data found");
    }
}

How to use it: #

Same as the reflection approach—just pass your dynamic data variable to the helper method:

String surveyValue = DummyData.getDynamicSurveyValue(data);

Bonus: If you ever need to update a survey value, update the Map first and sync the static variable (or just use the Map directly) to avoid data inconsistency.

Which one should you choose? #

• Use reflection if you can't modify the existing structure of DummyData or need to keep direct static variable access without changes.
• Use the Map approach if you want a more maintainable, readable solution with no reflection overhead.

内容的提问来源于stack exchange，提问作者AsifAli