Java 停车场设计

2025年5月12日 | 阅读 8 分钟

在 Java 面试中，最突出的问题之一就是停车场设计。Java 停车场设计是一个设计问题，涉及车辆如何在停车场内停放。这主要是在亚马逊、谷歌、Facebook 等顶级跨国公司的 HLD 或 LLD（高级或低级设计）轮次中提出的。请注意，这个问题没有绝对正确或错误的答案。因此，这类设计问题需要与面试官进行充分的讨论，了解面试官想要什么样的停车场设计。例如，一位面试官可能希望停车场有 5 层楼，而另一位面试官则对单层停车场感到满意。

在本节中，我们将使用 Java 的面向对象范例来设计停车场。在阅读本节之前，读者需要对 Java 的面向对象原则有充分的了解。

设计停车场

我们将根据下面描述的设计编写停车场的代码。

我们设计中包含的对象是车辆 (Vehicles)、停车场 (ParkingLot)、停车位 (Slots) 和楼层 (Levels)。

停车场 (ParkingLot): 有 'x' 层或楼层，每层有 'y' 个停车位。

楼层 (Levels): 每一层都是一个独立的实体，包含楼层号、其停车位以及其中的车道。

车道数量是根据停车位数量设计的。在本例中，10 个停车位构成 1 条车道。

停车位 (Slots): 一个停车位与其他停车位是独立的。停车位大小对车辆停放至关重要。例如，一个大车辆无法停放在一个小车位里。

车辆 (Vehicles): 包含公司名称、车辆编号及其类型。车辆有车牌和其所属公司的属性。

我们已将停车位和楼层视为独立的实体，这样以后可以为楼层添加任意数量的停车位。

每当车辆进出时，代表该车辆所属公司的车辆列表都会被更新。由于车辆的进入或离开，可用停车位的数量也会随之更新。

方法

parkVehicle(): parkVehicle() 方法会相应地停放车辆，同时还会考虑制造该车辆的公司。

leaveOperation(): 该操作负责让车辆 'V' 在楼层 'x' 离开。

companyParked(): CompanyParked() 方法方便用户查看特定公司停放的车辆列表。

停车场 Java 程序

完成设计部分后，我们就可以编写代码了。下面的程序使用了上述设计来创建一个停车场。

文件名: VSize.java

public enum VSize
{
    CarSize, Motorcycle,
}

文件名: Vehicle.java

// import statement
import java.util.ArrayList;

public abstract class Vehicle
{
// list of adding the slots that has been filled
protected ArrayList<ParkingSlot> parkingSlots = new ArrayList<ParkingSlot>();

// licence plate of the vehicle
protected String licPlate;

// field for the slot required by a vehicle
protected int slotsNeeded;

// size of the vehicle which is determined by the type of the vehicle
protected VSize siz;

// field of storing the company details from where the vehicle has come
// for example, if a car has come from Google, then companyName will be Google
protected String companyName;

// to get the slot required by a vehicle
public int getSlotsNeeded()
{
return slotsNeeded;
}

// the method adds the filled slot to the parkingSlots list
public void parkInSlot(ParkingSlot s)
{
parkingSlots.add(s);
}

// get the size of vehicle
public VSize getSize()
{
return siz;
}

public void clearSlots()
{
// remove car from slot, and notify the slot that the vehicle gone
for (int i = 0; i < parkingSlots.size(); i++)
{
parkingSlots.get(i).removeVehicle();
}
parkingSlots.clear();
}

// an abstract method that has to be defined by the child classess
public abstract boolean canFitInSlot(ParkingSlot spot);
}

文件名: Car.java

public class Car extends Vehicle
{
// constructor of the class Car
public Car(String licPlate, String companyName)
{
slotsNeeded = 1;
siz = VSize.CarSize;
this.licPlate = licPlate;
this.companyName = companyName;
}

public boolean canFitInSlot(ParkingSlot spot)
{
// checks if the spot is suitable for a car
return spot.getSize() == VSize.CarSize;
}
}

文件名: Motorcycle.java

public class Motorcycle extends Vehicle
{
// constructor of the class Motorcycle 
public Motorcycle(String licPlate, String companyName)
{
slotsNeeded = 1;
siz = VSize.Motorcycle;
this.licPlate = licPlate;
this.companyName = companyName;
}

public boolean canFitInSlot(ParkingSlot slot) 
{
// checks if the slot is a compact, motorcycle or a large

return slot.getSize() == VSize.CarSize || slot.getSize() == VSize.Motorcycle;
}
}

文件名: Lvl.java

// represents a level in the parking lot
public class Lvl
{
private int floor;
private ParkingSlot[] slots;	// number of slots in each level, including large, compact and motorcycle size
private int availableSlots = 0;	// number of free slots

// in each row at max there can be 10 slots
private static final int SLOT_PER_ROW = 10;

// constructor of the class Lvl
public Lvl(int flr, int numberSlots)
{
floor = flr;
availableSlots = numberSlots;
slots = new ParkingSlot[numberSlots];
int largeSlots = numberSlots / 4;
int bikeSlots = numberSlots / 4;
int compactSlots = numberSlots - largeSlots - bikeSlots;

for (int j = 0; j < numberSlots; j++)
{
VSize siz = VSize.Motorcycle;
if (j < largeSlots + compactSlots)
{
siz = VSize.CarSize;
}
int row = j / SLOT_PER_ROW;
slots[j] = new ParkingSlot(this, row, j, siz);
}
}

public int availableSlots()
{
return availableSlots;
}

public boolean parkVehicle(Vehicle vh)
{
//find a place to park this vehicle, return false if failed
if (availableSlots() < vh.getSlotsNeeded())
return false;

int slotNumber = findAvailableSlots(vh);
if (slotNumber < 0)
return false;
System.out.print(", Slot Number " + slotNumber);
return parkStartingAtSlot(slotNumber, vh);
}
private boolean parkStartingAtSlot(int num, Vehicle vh)
{
// park a vehicle at the slot slotNumber, and continuing till vehicle.slotsNeeded
vh.clearSlots();
boolean success = true;
for (int j = num; j < num + vh.slotsNeeded; j++)
{
success &= slots[j].park(vh);
}
availableSlots = availableSlots - vh.slotsNeeded;
return success;
}

// a method to find the vacant slot
private int findAvailableSlots(Vehicle vh)
{
int slotsNeeded = vh.getSlotsNeeded();
int lastRow = -1;
int slotsFound = 0;

for (int j = 0; j < slots.length; j++)
{
ParkingSlot spot = slots[j];
if (lastRow != slots[j].getLane())
{
slotsFound = 0;
lastRow = slots[j].getLane();
}
if (slots[j].canFitVehicle(vh))
{
slotsFound = slotsFound + 1;
}
else
{
slotsFound = 0;
}
if (slotsFound == slotsNeeded)
{
if(vh.siz == VSize.CarSize)
System.out.print("It is a Car parked in ");
else
System.out.print("It is a Motorcycle parked in ");
System.out.print("Lane Number  " + lastRow);
return j - (slotsNeeded - 1);
}
}
return -1;
}

// when the vehicle leaves the parking lot
// the numbyer of available slot increases by 1
public void slotFreed()
{
availableSlots = availableSlots + 1;
System.out.println("Available Slots in the current level :" + availableSlots);
}
}

文件名: ParkingSlot.java

public class ParkingSlot 
{
// fields of the class
private Vehicle vh;
private VSize siz;
private int lane;
private int slotNumber;
private Lvl l;

// constructor of the class
public ParkingSlot(Lvl lvl, int r, int num, VSize vs) 
{
l = lvl;
lane = r;
slotNumber = num;
siz = vs;
}


public boolean isAvailable() 
{
return vh == null;
}

public boolean canFitVehicle(Vehicle vh) 
{
//check if the spot is big enough and is available
return isAvailable() && vh.canFitInSlot(this);
}

public boolean park(Vehicle vObj) 
{
if (!canFitVehicle(vObj))
{
return false;
}

vh = vObj;
vh.parkInSlot(this);
return true;
}

// get method for lane
public int getLane() 
{
return lane;
}

// get method for slot number
public int getSlotNumber() 
{
return slotNumber;
}

// get method for getting the Size
public VSize getSize() 
{
return siz;
}

// method for removing the vehicle from the parking lot
public void removeVehicle() 
{
l.slotFreed();
vh = null;
}
}

文件名: ParkingLot.java

// important import statements
import java.util.ArrayList;
import java.util.*;
import java.util.HashMap;


// Creates a Parking Lot with the Number of levels and the slots in each of the given 
// levels.
public class ParkingLot
{
private Lvl[] lvls;
private final int NUM_LVLS = 2;
private int numberSlots;

// key contains the company name and 
// value is the vehicles present in the list
Map<String, ArrayList<String>> CompanytoVeh;

// constructor of the class
public ParkingLot(int numberSlots)
{
this.numberSlots = numberSlots;
this.CompanytoVeh = new HashMap<String, ArrayList<String>>();
lvls = new Lvl[NUM_LVLS];
for (int j = 0; j < NUM_LVLS; j++)
{
lvls[j] = new Lvl(j, numberSlots);
System.out.println("Level " + j + " created with " + numberSlots + " " +  "slots");
}
}

// a method for handling the scenario when a vehicle is parked
public boolean parkVehicle(Vehicle vh)
{
System.out.println(" ------------------------------------ ");

for (int i = 0; i < lvls.length; i++)
{
if (lvls[i].parkVehicle(vh)) 
{
System.out.println(" Level " + i + " with Vehicle Number " + vh.licPlate + " from " + vh.companyName);
if (this.CompanytoVeh.containsKey(vh.companyName)) 
{
ArrayList<String> regNoList = this.CompanytoVeh.get(vh.companyName);
this.CompanytoVeh.remove(vh.companyName);
regNoList.add(vh.licPlate);
this.CompanytoVeh.put(vh.companyName, regNoList);
} 
else 
{
ArrayList<String> regNoList = new ArrayList<String>();
regNoList.add(vh.licPlate);
this.CompanytoVeh.put(vh.companyName, regNoList);
}
return true;
}
}
System.out.println("PARKING IS FULL");
return false;
}

// method for handling the scenario when a vehicle leaves
public boolean leave(Vehicle vh, int lvl)
{
System.out.println(" ------------------------------------------ ");
lvls[lvl].slotFreed();
System.out.println("Slot freed from  Level " + lvl + " and exited  " + vh.licPlate + " of " + vh.companyName);
ArrayList<String> vhList = this.CompanytoVeh.get(vh.companyName);

// check if the vehicle is present in the list or not
// if present, remove the vehicle from the list
if (vhList.contains(vh.licPlate)) 
{
vhList.remove(vh.licPlate);
}

return true;
}

// method for displaying the list of vehicle of the given company
public void ComapnyParked(String companyName)
{
System.out.println(" ------------------------------------------ ");
ArrayList<String> vhList = this.CompanytoVeh.get(companyName);
System.out.print("The vehicles of " + companyName + " : ");
for(String vl : vhList)
{
System.out.print(vl + "\t");
}
System.out.println();
}
}

文件名: Main.java

public class Main 
{
// main mehtod
public static void main(String argvs[]) 
{
// creating an object of the class ParkingLot
ParkingLot pl = new ParkingLot(2);

// car1 has license number 1234 and the company name is Microsoft
Car car1 = new Car("1234", "Microsoft");

// m1 has license number 4016 and the company name is Microsoft
Motorcycle m1 = new Motorcycle("4016", "Microsoft");

// car2 has license number 1609 and the company name is Google
Car car2 = new Car("1609", "Google");

// m2 has license number 1389 and the company name is Google
Motorcycle m2 = new Motorcycle("1389", "Google");

// car3 has license number 1809 and the company name is Microsoft
Car car3 = new Car("1809", "Microsoft");

//  parking the vehicles
pl.parkVehicle(car1);
pl.parkVehicle(m1);
pl.parkVehicle(car2);

// for displaying the list of vehicles that has company name Microsoft
pl.ComapnyParked("Microsoft");

// for displaying the list of vehicles that has company name Google
pl.ComapnyParked("Google");

pl.leave(m1,0); // Note that m1 is from Microsoft


// for displaying the list of vehicles that has company name Microsoft
pl.ComapnyParked("Microsoft");


pl.parkVehicle(m2);
pl.parkVehicle(car3);


}
}

输出

Level 0 created with 2 slots
Level 1 created with 2 slots
 ------------------------------------
It is a Car parked in Lane Number 0, Slot Number 0 Level 0 with Vehicle Number 1234 from Microsoft
 ------------------------------------
It is a Motorcycle parked in Lane Number 0, Slot Number 1 Level 0 with Vehicle Number 4016 from Microsoft
 ------------------------------------
It is a Car parked in Lane Number 0, Slot Number 0 Level 1 with Vehicle Number 1609 from Google
 ------------------------------------------
The vehicles of Microsoft: 1234        4016
 ------------------------------------------
The vehicles of Google: 1609
 ------------------------------------------
Available Slots in the current level :1
Slot freed from Level 0 and exited 4016 of Microsoft
 ------------------------------------------
The vehicles of Microsoft: 1234
 ------------------------------------
It is a Motorcycle parked in Lane Number 0, Slot Number 1 Level 1 with Vehicle Number 1389 from Google
 ------------------------------------
PARKING IS FULL

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