Question

给出客户需求任务。

•创建包含车辆ID（整数）作为车辆的车辆类号和地块（整数）作为停车场号。实现getId（）和 getLot（）返回车辆ID和批次。

创建包含parkedVehicle，vehicle_lot_data并实现以下内容的ParkingLot类

HashMap<Integer, Vehicle> parkedVehicle = new HashMap<>(); 
HashMap<Integer, Integer> vehicle_lot_data = new HashMap<>();

•parkVehicle（车辆，地段）将车辆停在该地段，检查是否有效停车，并检查同一车辆不允许在多批。如果已经预订了很多物品，则返回“拍品已提取” 如果我们要预订的话，有人和“车辆已经在场” 同一辆车有多个批次。 •isLotBooked（int lot）返回布尔值-检查已预订的批次。返回假空的则为True，而预订的则为True。 •isVehicleExists（int vehicleId）return boolean-检查已经存在的车辆。如果车辆存在则返回True，否则返回False 车辆。

步骤3：（Database.java）

创建一个类别数据库来存储停车场数据。

创建本地SQLite数据库（parking_database.db）•创建 DATABASE_NAME变量并存储parking_database.db。 • 实行用于数据库创建和数据库删除的onCreate，onUpgrade。 •ParkVehicle（Vehicle）-将停放的车辆保存到数据库。 •getParkedVehicle（），getParkedVehicle（int vehicleId）-获取所有停放的车辆返回（Cursor）•getAllBookedLots（）-获取所有预订停车场返回（光标）

具有以下架构的设计表

CREATE TABLE parking_lots (id integer PRIMARY KEY, 
lot_number INTEGER, 
vehicle_number INTEGER UNIQUE);

•实现ParkVehicleNow（），它将从视图中获取用户输入数据，并将数据存储在这些变量vehicle_id_field_txt和将会呼叫停车的vehicle_lot_number_field_txt（int vehicle_id_field_txt，int vehicle_lot_number_field_txt）函数内部。 •park（int vehicle_id_field_txt，int vehicle_lot_number_field_txt）-将使用ParkingLot类和使用ParkingLot实例pl停放车辆并将该车辆保存到数据库使用Databaseclass实例db。 •如果您不能停车然后制作“已停放的吐司面包”，请选择其他批次或车辆”，否则将“已停放车辆”消息。 •另外，不要忘记对“已采取拍品”和“车辆”执行验证已经存在”，则不要停放车辆。

但是我没有得到如何在ParkingLot中实现哈希图的步骤2。

我很累的是，根据情况，在这里我无法在任何地方使用哈希图。

public class ParkingLot {
    HashMap<Integer, Vehicle> parkedVehicle = new HashMap<>();
    HashMap<Integer, Integer> vehicle_lot_data = new HashMap<>();

    public boolean isLotBooked(int lot, Context context) {
        Database db = new Database(context);
        return db.isAlreadyLotsExists(String.valueOf(lot));
    }

    public boolean isVehicleExists(int vehicleId, Context context) {
        Database db = new Database(context);
        return db.isAlreadyVehicleExists(String.valueOf(vehicleId));
    }

}


  public Vehicle(){

    }

    public Vehicle(int primaryId,int id, int lot){
        this.id = id;
        this.lot = lot;
        this.primaryId = primaryId;
    }
    public Vehicle(int id, int lot){
        this.id = id;
        this.lot = lot;
    }
    public int id;

    public int getPrimaryId() {
        return primaryId;
    }

    public void setPrimaryId(int primaryId) {
        this.primaryId = primaryId;
    }

    public int primaryId;

    public int getId() {
        return id;
    }

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

    public int getLot() {
        return lot;
    }

    public void setLot(int lot) {
        this.lot = lot;
    }

    public int lot;

}


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Database db = new Database(this);
        db.ParkVehicle(new Vehicle(1000,1));
        db.ParkVehicle(new Vehicle(2000,2));

        // Reading all contacts
        Log.e("Reading: ", "Reading all contacts..");
        List<Vehicle> contacts = db.getParkedVehicle(); //all parked vehicle
        List<String> bookedSlots = db.getAllBookedLots(); //all booked slots

        for (Vehicle cn : contacts) {
            String log = "Id: " + cn.getPrimaryId() + " ,Vehicle: " + cn.getId() + " ,Lot: " +
                    cn.getLot();
            // Writing Contacts to log
            Log.e("ContactsAllVehicles: ", log);
        }

        for (String cn : bookedSlots) {
            // Writing Contacts to log
            Log.e("ContactsSlots: ", cn);
        }

        Vehicle vehicle= db.getParkedVehicle(1);
        Log.e("ContactsLots",""+vehicle.getId());

        //checking if lots already exisitng..
        boolean alreadyExist=db.isAlreadyLotsExists("0");
        Log.e("contactsslotsTest",""+alreadyExist);
    }



public class Database extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "vehicles";
    private static final String KEY_ID = "id";
    private static final String LOT_NUMBER = "lot_number";
    private static final String VEHICLE_NUMBER = "vehicle_number";
    private static final String PARKING_LOTS = "parking_lots"; //table name

    public Database(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        //3rd argument to be passed is CursorFactory instance
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + PARKING_LOTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + LOT_NUMBER + " INTEGER,"
                + VEHICLE_NUMBER + " INTEGER UNIQUE" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + PARKING_LOTS);

        // Create tables again
        onCreate(db);
    }

    void ParkVehicle(Vehicle contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(LOT_NUMBER, contact.getLot()); // Lot number
        values.put(VEHICLE_NUMBER, contact.getId()); // Vehicle number

        // Inserting Row
        db.insert(PARKING_LOTS, null, values);
        //2nd argument is String containing nullColumnHack
        db.close(); // Closing database connection
    }

    Vehicle getParkedVehicle(int id) { //single vehicle
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(PARKING_LOTS, new String[]{KEY_ID,
                        LOT_NUMBER, VEHICLE_NUMBER}, KEY_ID + "=?",
                new String[]{String.valueOf(id)}, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Vehicle contact = new Vehicle(Integer.parseInt(cursor.getString(0)),
                Integer.parseInt(cursor.getString(1)), Integer.parseInt(cursor.getString(2)));
        // return contact
        return contact;
    }

    public List<Vehicle> getParkedVehicle() {
        List<Vehicle> contactList = new ArrayList<Vehicle>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + PARKING_LOTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Vehicle contact = new Vehicle();
                contact.setPrimaryId(Integer.parseInt(cursor.getString(0)));
                contact.setLot(Integer.parseInt(cursor.getString(1)));
                contact.setId(Integer.parseInt(cursor.getString(2)));
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

    public List<String> getAllBookedLots(){
        List<String> contactList = new ArrayList<>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + PARKING_LOTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        cursor.moveToFirst();

        // looping through all rows and adding to list
        if (cursor!=null && cursor.moveToFirst()) {
            while(cursor.isAfterLast() == false){
                contactList.add(cursor.getString(cursor.getColumnIndex(LOT_NUMBER)));
                Log.d("contactslotnumber",contactList.toString());

                cursor.moveToNext();
            }}
        return contactList;
    }

    public boolean isAlreadyLotsExists(String name){
            SQLiteDatabase sqLiteDatabase = this.getReadableDatabase();
            String query="SELECT * FROM "+PARKING_LOTS+" WHERE "+LOT_NUMBER+" = "+name;
            Cursor cursor = sqLiteDatabase.rawQuery(query,null);
            if(cursor.getCount()>0)
                return true;
            else
                return false;

    }

    public boolean isAlreadyVehicleExists(String name){
        SQLiteDatabase sqLiteDatabase = this.getReadableDatabase();
        String query="SELECT * FROM "+PARKING_LOTS+" WHERE "+VEHICLE_NUMBER+" = "+name;
        Cursor cursor = sqLiteDatabase.rawQuery(query,null);
        if(cursor.getCount()>0)
            return true;
        else
            return false;

    }

        // return contact list



    public int updateContact(Vehicle contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(LOT_NUMBER, contact.getLot());
        values.put(VEHICLE_NUMBER, contact.getId());

        // updating row
        return db.update(PARKING_LOTS, values, KEY_ID + " = ?",
                new String[]{String.valueOf(contact.getPrimaryId())});
    }

    // Deleting single contact
    public void deleteContact(Vehicle contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(PARKING_LOTS, KEY_ID + " = ?",
                new String[]{String.valueOf(contact.getPrimaryId())});
        db.close();
    }

    // Getting contacts Count
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + PARKING_LOTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        // return count
        return cursor.getCount();
    }
}

这是我所做的，但是需求中缺少一些步骤。比如说：步骤2我不确定在哪里使用哈希图在ParkingLot类中使用parkVehicle方法，在MainActivity中也类似地使用步骤4。

Answer 1

可能是在缓存数据库数据的上下文中给出了哈希图。当您写入与车辆/批次相关的数据时，您将哈希图用作缓存（利用回写或直写策略，无论哪种方式都符合您的要求或需求），并且在读取数据时，始终会从哈希图读取它们，即缓存< / p>

回想一下，回写意味着您将新数据写入缓存，但不写入DB（稍后将数据写入DB），而直写意味着每当您写入新数据时，都会将其写入两个缓存和数据库

在这种情况下如何使用HashMap？

1 个答案: