如何在启动另一个活动后保留变量

Question

当我尝试访问已在以下类中初始化的列表锦标赛时：

public class AdminControl extends AppCompatActivity {

    Firebase ref;
    FloatingActionButton fab;
    public static List <Tournament> tournaments;
    ListView list;
    Tournament [] temp;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_control);
        Toolbar b = (Toolbar) findViewById(R.id.toolbar);
        b.setTitle("Tournaments");
        setSupportActionBar(b);
        fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                createNewTournament(v);
            }
        });
        AdminLogin.firebase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                tournaments = (ArrayList) dataSnapshot.getValue();
                Object [] objArr = tournaments.toArray();
                temp = new Tournament[objArr.length];
                for (int i = 0; i < objArr.length; i++){
                    temp[i] = (Tournament) objArr[i];
                }
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });
        if (tournaments == null){
            tournaments = new ArrayList<Tournament>();
        }
        list = (ListView) findViewById(R.id.listView);
        ArrayAdapter<Tournament> tempAdapter = new ArrayAdapter<Tournament>(
                this, android.R.layout.simple_list_item_1, temp);
        list.setAdapter(tempAdapter);
    }

    public void createNewTournament(View v) {
        Intent newIntent = new Intent(this, TournamentCreator.class);
        startActivity(newIntent);
    }
}

在我离开该任务并通过调用上面的TournamentCreator方法createNewTournament实例化新活动后，我尝试从static访问TournamentCreator列表锦标赛活动。但是，它显示为null（Object a）。我认为静态变量总是保持不变。在我正在做的事情中是否存在某种问题？

比赛创作者类

public class TournamentCreator extends AppCompatActivity {
    private Button b;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Object a = AdminControl.tournaments;
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tournament_creator);
        b = (Button) findViewById(R.id.button3);
        b.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                beginTournament(v);
            }
        });
    }

    public void beginTournament(View v) {
        EditText text = (EditText) findViewById(R.id.editText);
        Tournament newTourn = new Tournament(text.getText().toString());
        AdminControl.tournaments.add(newTourn);
        Firebase userRef = AdminLogin.firebase.child("users").child(AdminLogin.firebase.getAuth().getUid());
        userRef.setValue(AdminControl.tournaments);
        finish();
    }
}