静态引用被清除——如果未使用，Android 是否会在运行时卸载类?

The problem is this: We're currently trying to cut down on singleton classes in the app in favor of a single root factory singleton which sole purpose is to manage other manager classes. A top level manager if you will. This makes it easy for us to replace implementations in tests without opting for a full DI solution, since all Activities and Services share the same reference to that root factory.

它是这样的:

public class RootFactory {

    private static volatile RootFactory instance;

    @SuppressWarnings("unused")
    private Context context; // I'd like to keep this for now

    private volatile LanguageSupport languageSupport;
    private volatile Preferences preferences;
    private volatile LoginManager loginManager;
    private volatile TaskManager taskManager;
    private volatile PositionProvider positionManager;
    private volatile SimpleDataStorage simpleDataStorage;

    public static RootFactory initialize(Context context) {
        instance = new RootFactory(context);
        return instance;
    }

    private RootFactory(Context context) {
        this.context = context;
    }

    public static RootFactory getInstance() {
        return instance;
    }

    public LanguageSupport getLanguageSupport() {
        return languageSupport;
    }

    public void setLanguageSupport(LanguageSupport languageSupport) {
        this.languageSupport = languageSupport;
    }

    // ...
}

initialize 被调用一次，在 Application.onCreate 中，即 在任何 Activity 或 Service 启动之前.现在，问题来了:getInstance 方法有时会以 null 的形式返回——即使在同一个线程上调用也是如此！听起来这不是能见度问题.相反，类级别的静态单例引用保留似乎实际上已被垃圾收集器清除.也许我在这里草率下结论，但这可能是因为 Android 垃圾收集器或类加载机制实际上可以在内存不足时 unload 类，在这种情况下，对单例实例的唯一引用将消失离开?我对 Java 的内存模型并不是很深入，但我认为这不应该发生，否则这种实现单例的常用方法在任何 JVM 上都不起作用，对吧?