基于Android java实现创建DAO类对Sqlite数据库的增删改查操作进行封装，给出其中User类的源码

好的，下面是基于Android Java实现创建DAO类对SQLite数据库的增删改查操作进行封装，其中User类的源码：

public class User {
    private int id;
    private String username;
    private String password;

    public User() {}

    public User(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }
}

DAO类的实现：

public class UserDao {
    private SQLiteDatabase db;

    public UserDao(Context context) {
        DatabaseHelper dbHelper = new DatabaseHelper(context);
        db = dbHelper.getWritableDatabase();
    }

    public void add(User user) {
        ContentValues values = new ContentValues();
        values.put("username", user.getUsername());
        values.put("password", user.getPassword());
        db.insert("user", null, values);
    }

    public void delete(int id) {
        db.delete("user", "id=?", new String[]{String.valueOf(id)});
    }

    public void update(User user) {
        ContentValues values = new ContentValues();
        values.put("username", user.getUsername());
        values.put("password", user.getPassword());
        db.update("user", values, "id=?", new String[]{String.valueOf(user.getId())});
    }

    public User queryById(int id) {
        Cursor cursor = db.query("user", null, "id=?", new String[]{String.valueOf(id)}, null, null, null);
        User user = null;
        if (cursor.moveToFirst()) {
            user = new User();
            user.setId(cursor.getInt(cursor.getColumnIndex("id")));
            user.setUsername(cursor.getString(cursor.getColumnIndex("username")));
            user.setPassword(cursor.getString(cursor.getColumnIndex("password")));
        }
        cursor.close();
        return user;
    }

    public List<User> queryAll() {
        List<User> userList = new ArrayList<>();
        Cursor cursor = db.query("user", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            User user = new User();
            user.setId(cursor.getInt(cursor.getColumnIndex("id")));
            user.setUsername(cursor.getString(cursor.getColumnIndex("username")));
            user.setPassword(cursor.getString(cursor.getColumnIndex("password")));
            userList.add(user);
        }
        cursor.close();
        return userList;
    }
}

其中，DatabaseHelper类是一个继承自SQLiteOpenHelper的辅助类，用于创建和更新数据库：

public class DatabaseHelper extends SQLiteOpenHelper {
    public DatabaseHelper(Context context) {
        super(context, "mydb.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table user(id integer primary key autoincrement, username varchar(20), password varchar(20))");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists user");
        onCreate(db);
    }
}

以上代码实现了User类的增删改查，同时对SQLite数据库的操作进行了封装，使得使用更加方便。