How to retrieve values in the firebase realtime database

Question

I am struggling with retrieving data from the firebase.

For example, I want to get the first record and get the username & password. How can I get the "key" of the first record?

Here is my code:

    private String UserName;
    private String Password;
    private int Identity;
    private DatabaseReference reff = FirebaseDatabase.getInstance().getReference();

    public User() {

    }

    public User(String UserName, String Password, int Identity) {
        this.UserName = UserName;
        this.Password = Password;
        this.Identity = Identity;

    }

    public String getUserName() {
        return UserName;
    }

    public void setUserName(String UserName){
        this.UserName = UserName;
    }

    public String getPassword() {
        return Password;
    }

    public void setPassword(String Password) {
        this.Password = Password;
    }

    public int getIdentity() {
        return Identity;
    }

    public void setIdentity(int identity) {
        Identity = identity;
    }

    public void Save(){
        reff.child("Users").push().setValue(this);
    }
}

User newUser = new User(userName, password, identity);
                newUser.Save();

Answer 1

If you want to get the key of the item you are writing, you can see it with:

public void Save(){
    DatabaseReference newUserRef = reff.child("Users").push();
    newUserRef.setValue(this);
    System.out.println(newUserRef.getKey());
}

If you want to find the key while you're reading the users, you can show them with:

DatabaseReference usersRef = reff.child("Users");
usersRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
            System.out.println(userSnapshot.getKey());
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
}