java - 从另一个静态变量构造函数调用静态变量

Question

在我的 Android 应用程序中，我必须在第一个 Activity 启动之前初始化许多静态对象。据我所知，静态变量是在加载类时初始化的。因此，随着时间的推移，项目中静态对象的数量开始增长，现在我遇到了 NullPointerExceptions。就我而言，静态对象可以在其构造函数中调用其他静态对象。所以我的问题是:某些静态变量是否可以在它们依赖的变量之前初始化，从而导致 NullPointersExceptions？那可能吗？代码示例:

private static class HardwareManagersHolder implements HardwareManagers, IManagers {

        private final AtomicBoolean senderAcquire = new AtomicBoolean(false);
        private final AtomicInteger receiverAcquire = new AtomicInteger(0);
        public IAudioManager audioManager;
        public IVideoManager videoManager;
        public IVibrationManager vibrationManager;
        public IBatteryHelper batteryHelper;

        @Override
        public void configureManager() {
            audioManager = AudioHelper.getInstance();
            vibrationManager = VibrationManager.getInstance();
            videoManager =  VideoManager.getInstance();
            batteryHelper = BatteryHelper.getInstance();
        }

还有一个物体支架:

public class VideoManager implements IVideoManager {
    private static class VideoManagerHolder {
            public static final VideoManager VIDEO_MANAGER_INSTANCE = new VideoManager();
        }


    public static VideoManager getInstance() {
        return VideoManagerHolder.VIDEO_MANAGER_INSTANCE;
    }

}

Answer 1

我尝试用您提供的 fragment 重建您的异常。我使用了以下代码:

public interface IVideoManager {}


public class VideoManager implements IVideoManager {


  private static class HardwareManagersHolder {

    public IVideoManager videoManager;

    public void configureManager() {
      videoManager = VideoManager.getInstance();
    }
  }

  private static class VideoManagerHolder {

    public static final VideoManager VIDEO_MANAGER_INSTANCE = new VideoManager();
  }

  public static VideoManager getInstance() {
    return VideoManagerHolder.VIDEO_MANAGER_INSTANCE;
  }

  public static void main(String[] arg) {
    System.out.println("Start test");
    HardwareManagersHolder h = new HardwareManagersHolder();
    h.configureManager();
    if (h.videoManager == null) {
      System.out.println("VideoManager is null");
    }
    System.out.println("Test finished");
  }

}

这段代码可以在我的机器上运行。如果此代码不适用于您的代码，则可能存在其他错误。