finding the sum of the score and sorting it firebase android

I would like to find all the users data and sum of their scores on particular questions and find the highest rank

I have multiple nodes with unique user id now I would like to find the sum of all the values inside the question node.

This is how I have created my POJO

private String id;
private String name;
private String contact;
private String email;
private String password;
private int score;
private String dob;
private String profession;
private String random;
private String status;
private String fbId;
private UserPuzzleDetails userPuzzleDetails;
public User() {
}
public User(String id, String name, String contact, String email, String password, int score, String dob, String profession, String random, String status, String facebookid, UserPuzzleDetails userPuzzleDetails1) { this.id = id; this.name = name; this.contact = contact; this.email = email; this.password = password; this.score = score; this.dob = dob; this.profession = profession; this.random = random; this.status = status; this.fbId = facebookid; this.userPuzzleDetails = userPuzzleDetails1;
}
public User(String id, String name, String contact, String email, String password, int score, String dob, String profession, String random, String status, String facebookid) { this.id = id; this.name = name; this.contact = contact; this.email = email; this.password = password; this.score = score; this.dob = dob; this.profession = profession; this.random = random; this.status = status; this.fbId = facebookid;
}
public User(String name) { this.name = name;
}
public String getId() { return id;
}
public void setId(String id) { this.id = id;
}
public String getName() { return name;
}
public void setName(String name) { this.name = name;
}
public String getEmail() { return email;
}
public String getPassword() { return password;
}
public int getScore() { return score;
}
public void setScore(int score) { this.score = score;
}
public String getContact() { return contact;
}
public String getDob() { return dob;
}
public String getProfession() { return profession;
}
public String getRandom() { return random;
}
public UserPuzzleDetails getUserPuzzleDetails() { return userPuzzleDetails;
}
public void setUserPuzzleDetails(UserPuzzleDetails questions) { this.userPuzzleDetails = questions;
}
public String getStatus() { return status;
}
public String getFbId() { return fbId;
}
public void setFbId(String fbId) { this.fbId = fbId;
}

Now I have used this function to retrieve the data but it is not logging. How should I go by this data iterate through it.

 private void getAllRank() { final DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference().child("users"); final Query query = databaseReference.orderByChild("score").limitToLast(10); query.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { userlist = new ArrayList<>(); for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) { User score = postSnapshot.getValue(User.class); userlist.add(new User(score.getId(), score.getName(), score.getContact(), score.getEmail(), score.getPassword(), score.getScore(), score.getProfession(), score.getDob(), score.getRandom(), score.getStatus(), score.getFbId(),score.getUserPuzzleDetails())); Log.e(TAG, "onDataChange: "+userlist ); } } @Override public void onCancelled(DatabaseError databaseError) { } });
}