在尝试调用反射方法时引发

Question

static void setFinalStatic(Field field, Object newValue) throws Exception {
        field.setAccessible(true);
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true); 
        modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
        field.set(null, newValue);
    }

 Time elapsed: 2.383 s  <<< FAILURE!

java.lang.NoSuchFieldException: modifiers
        at java.base/java.lang.Class.getDeclaredField(Class.java:2412)

public class MyApiService extends RestApiService {



    private MyApiService(String baseURL, String user, String password) {
        super(baseURL, user, password);

    }


    /**
     * Singleton holder class for the MyApiService object
     */
    private static class SingletonHolder {
        private static final ACPConfig ACP_CONFIG = (ACPConfig) 
        private static final Config PLATFORM_AO_CONFIG = ACP_CONFIG.newConfig
                .getConfig(“def”)
                .getConfig("abc”);
        private static final String BASE_URL = PLATFORM_AO_CONFIG.getString("url");
        private static final String USER = PLATFORM_AO_CONFIG.getString("user");
        private static final String PASSWORD = PLATFORM_AO_CONFIG.getString("password");
        private static final MyApiService INSTANCE = new MyApiService(BASE_URL, USER, PASSWORD);
    }

    /**
     * Creates a singleton object of this class
     *
     * @return <code>MyApiService</code> singleton object
     */
    public static MyApiService getInstance() {
        return SingletonHolder.INSTANCE;
    }

for (Class nclass : MyApiService.class.getDeclaredClasses()) {
    System.out.println("SimpleName is "+nclass.getSimpleName());
    if (nclass.getSimpleName().equals("SingletonHolder")) {
        sclass = nclass;

        System.out.println(" sclass is " + sclass.getSimpleName());

        for (Field field : sclass.getDeclaredFields()) {
            System.out.println("Field names are " + field.getName());
        }

        setFinalStatic(sclass.getDeclaredField("PLATFORM_AO_CONFIG"), null);
        setFinalStatic(sclass.getDeclaredField("USER "), null);
        setFinalStatic(sclass.getDeclaredField(" PASSWORD"), null);
        break;
    }
}

Answer 1

不能更改静态final字段。这并不是因为这是规则（它确实是），而是因为当您的代码运行时，字段甚至不再存在。在任何地方使用它，编译器只是使用该值。所以这两个代码块编译成完全相同的。

someObject.callSomeMethod(12);

而且

static final int INCHES_PER_FOOT = 12;

someObject.callSomeMethod(INCHES_PER_FOOT);

所以，基本上，您要求使用反射将数字12更改为其他的东西。尝试都没有意义。