Android Same instance output different result

Question

I outputted the same object at the same time but I got different results... What could be the cause of DIFFERENT result?

The function in UserHelper.class:

public void login(String phone, String password) {
 UserModel.logInInBackground(phone, password, new LogInCallback<UserModel>() {
 @Override
 public void done(UserModel userModel, AVException e) {
 if (null != userModel) {
 if (userModel.getPosition() == UserModel.USER_BUYER) {
 refresh();
 DebugLog.e("fuck" + mUserStatus + UserInstance.getInstance().getUserStatus());
 for (UserListener listener : listeners)
 listener.OnUserLogin();
 } else if (userModel.getPosition() == UserModel.USER_SELLER)
 logout();
 } else for (UserListener listener : listeners)
 listener.HandleError(e.getCode());
 }
 }, UserModel.class);
public USER_STATUS getUserStatus() {
 return mUserStatus;
}

And the UserInstance.class.

public class UserInstance {
 public static UserHelper mInstance;
public static UserHelper getInstance() {
 if (null == mInstance) mInstance = new UserHelper();
 DebugLog.e(mInstance.toString());
 return mInstance;
 }
}

• agi: Which objects exactly should be the same? mUserStatus and UserInstance.getInstance().getUserStatus()? And which class contains the login method?
• Aquarids: yes public USER_STATUS getUserStatus() { return mUserStatus; }
• agi: so login(..) is a method of the UserHelper?! Did you debug to the line, in which you logged the objects, to compare the object ids? I would need more code - where do you call the login-method?
• Shadab Ansari: Does your UserModel.logInInBackground() runs in UI thread or separate thread ?
• Aquarids: In the first Activity when user click login button I call the login-method. And I logged the objects it do have different ids but I do not know why...

Answer 1

First of all, if you meant the UserHelper class to be a singleton, why do you access the USER_STATUS instance using UserInstance.getInstance().getUserStatus() instead of just getUserStatus() ?

Second of all, you probably get different instances of UserHelper if the singleton is accessed from different threads, because your implementation is not thread-safe.

A correct implementation would be using a double locking pattern:

public class UserInstance {
 public static UserHelper mInstance;
 private static final ReentrantLock lock = new ReentrantLock();
 public static UserHelper getInstance() {
 if (null == mInstance){
 lock.lock();
 try{
 if (null == mInstance){
 mInstance = new UserHelper();
 }
 }
 finally{
 lock.unlock();
 }
 }
 DebugLog.e(mInstance.toString());
 return mInstance;
 }

}

Answer 2

Ultimately, I get the same instance..

Thanks to Shlomi Uziei. I forgot to use double locking pattern. And I should not make mInstance static...