sqlite的使用

public class DatabaseHelper extends SQLiteOpenHelper{

    public static final String DATABASE_NAME = "database";
    
 public static final int DATABASE_VERSION = 1;

   //构造方法可根据需求修改形参
    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    public DatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, DATABASE_NAME, factory, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table if not exists user (id integer primary key, name varchar(20), age integer)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

public class DatabaseManager {

    private DatabaseHelper dbHelper;
    
 private SQLiteDatabase db;

    public DatabaseManager(Context context){
        this.dbHelper = new DatabaseHelper(context);
    }

    public void openDB() {
      //getWritableDatabase()返回读写数据库的对象
        db = dbHelper.getWritableDatabase();
    }

    public void closeDB() {
        db.close();
    }

    public List<UserBean> queryAll() {
        List<UserBean> userList = new ArrayList<>();
        Cursor cursor = db.rawQuery("select * from user", null);
        while (cursor.moveToNext()){
            UserBean user = new UserBean(cursor.getInt(0), cursor.getString(1), cursor.getInt(2));
            userList.add(user);
        }
        cursor.close();
        return userList;
    }
}