I was trying to implement Room for persistent data storage in java. But I ran into problems with it.

In first try:

MyDao.java

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void addUser(UserDetails userDetails);

}

MyDatabase.java

@Database(entities = {User.class}, version = 1)
public abstract class MyDatabase extends RoomDatabase {

    public abstract MyDao myDao();
}

with the above the app crashes with error:
java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.
whenever I try to insert a data into the database.

In the second try:

MyDao.java

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    ListenableFuture<Integer> addUser(UserDetails userDetails);

}

MyDatabase.java

@Database(entities = {User.class}, version = 1)
public abstract class MyDatabase extends RoomDatabase {

    public abstract MyDao myDao();
}

changed the return type to hold ListenableFuture<Integer> because official doc says to do so. The app does not build successfully and shows the following error:
error: Not sure how to handle insert method's return type.

So, my question is how can I correctly and successfully insert data in the database using room with java.
Please help.

After wandering on the internet for ages, I came to know that it is possible to write insert query using following 2 methods:

1. Using a thread class

Operations.java

public class Operations{

    private MyDao myDao;

    public Operations(Context context){
        MyDatabase db = Room.databaseBuilder(context, MyDatabase.class, "database")
                .fallbackToDestructiveMigration()
                .build();
        myDao = db.myDao();
    }

    public void insertUser(UserDetails userDetails){
        new Thread{
            @override
            public void run(){
                myDao.addUser(userDetails);
            }
        }.start();
    }

}

MyDao.java

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void addUser(UserDetails userDetails);

}

MyDatabase.java

@Database(entities = {User.class}, version = 1)
public abstract class MyDatabase extends RoomDatabase {

    public abstract MyDao myDao();
}

OR

2. Using ExecutorService class

Operations.java

public class Operations{

    private MyDao myDao;

    public Operations(Context context){
        MyDatabase db = Room.databaseBuilder(context, MyDatabase.class, "database")
                .fallbackToDestructiveMigration()
                .build();
        myDao = db.myDao();
    }

    public void insertUser(UserDetails userDetails){
        MyDatabase.databaseWriteExecutor.execute(()->{
               notesDb.notesDao().addNote(note));
           }
    }

}

MyDao.java

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void addUser(UserDetails userDetails);

}

MyDatabase.java

@Database(entities = {User.class}, version = 1)
public abstract class MyDatabase extends RoomDatabase {
    
    public static final ExecutorService databaseWriteExecutor =
            Executors.newFixedThreadPool(2);

    public abstract MyDao myDao();
}