Java

Question

我有一个 class 依赖于我之前创建的三个 classes。我在第 4 个 class 中有一个方法，其中要求我获取最新的 Car 对象。如果有更多，从一个这样的，其中一个将被 return 任意编辑。调用的方法getNewest()

发布当前的 class 和之前的供您参考以建立联系：

前 3 class -> 汽车

public class Car {

private  Owner _owner; //an object from 1st class
private String _manufacturer;
private boolean _airbag;
private boolean _leasingOrRental;
private int _km, _seats, _year;
private int _price;
private int _LevyPrice;
private Bid _highestBid;//an object from 2st class

public Car(Owner ow, String mfr, boolean isAirbag, boolean leasOrRent, int kilNum, int seatNum, int date, int price, int levy, Bid high) // Constructor
{
    _owner = new Owner(ow);
    _manufacturer = mfr;
    _airbag = isAirbag;
    _leasingOrRental = leasOrRent;
    _km = kilNum;
    _seats = seatNum;
    _year = date;
    _price = price;
    _LevyPrice = levy;
    _highestBid = new Bid(high);
}

public Car(Car other) //copy constrcutor 
{
    _owner = new Owner(other._owner);
    _manufacturer = other._manufacturer;
    _airbag = other._airbag;
    _leasingOrRental = other._leasingOrRental;;
    _km = other._km;
    _seats = other._seats;;
    _year = other._year;
    _price = other._price;
    _LevyPrice = other._LevyPrice;
    _highestBid = new Bid(other._highestBid); 
}

public Owner getOwner()
{
    return new Owner(_owner);
}

public String getManufacturer()
{
    return _manufacturer;
}

public boolean getAirbag()
{
    return _airbag;
}

public boolean getIsleasingOrRental()
{
    return _leasingOrRental;
}

public int getKm() {
    return _km;
}

public int getSeats() {
    return _seats;
}

public int getYear() {
    return _year;
}

public int getLevyPrice() {
    return _LevyPrice;
}

public Bid getHighestBid() {
    return new Bid(_highestBid);
}

public void makeBid(Bid bid)
{
    if (_highestBid.getBidPrice() < bid.getBidPrice())
        _highestBid.setBidPrice(bid.getBidPrice());
}

public boolean isAttractive()
{
    return _airbag == true && _leasingOrRental == true && (_km > 0 && _km < 20000 ) && _year >= 3;
}

public boolean fitForFamily(int kids)
{
    return _seats - 2 >= kids;
}

public boolean overUsedCar()
{
    final int KILOMERTES = 12000;

    return _km > KILOMERTES*(2022 - _year);
}

public String toString()
{
    return "Manufacturer: "+_manufacturer+"\n"
            +"Year: "+_year+"\n"
            +"Owner: "+_owner.toString()+"\n"
            +"Highest bid: "+_highestBid.getBidPrice();
}

}

第 4 和当前 class CarSales 和

public class CarSales {

private Car[] _cars;
int _noOfCars;

public CarSales(int size)
{
    _cars = new Car[size];
    _noOfCars = 0;
}

public boolean addCar(Car car)
{
    int size = _cars.length+1;
    //_cars = new Car[_noOfCars];
    if(_cars.length < _noOfCars)
    {
        _cars[size] = new Car(car);
        return true;
    }
    else
    {
        return false;
    }
}

public Car getNewest()
{
    Car newest = _cars[0];
    Car [] _new = new Car[_noOfCars];
    int size = 0;
    for (int i = 1; i < _cars.length; i++)
        if(newest.getYear() < _cars[i].getYear())
            newest = _cars[i];

    for (int i = 0; i < _cars.length; i++)
        if (newest.getYear() == _cars[i].getYear())
            size++;

    for (int i = 0; i < _cars.length; i++)
        if (newest.getYear() == _cars[i].getYear())
            _new[i] = new Car(_cars[i]);

    return _new[0];
}
}

在我创建的方法中，我正在 return 第一个对象，但如果我从一开始就这样做，我可以在第一个循环之后 return 它。但是，如果我有多个对象，我想任意选择 return 对象。另外，如果有办法提高效率，我将不胜感激。

不能使用 ArrayList lang，如添加或复制或 indexOf 必须按逻辑进行。

提前感谢所有帮助者和反馈。

Answer 1

在 class CarSales 的构造函数中，您初始化 _cars。这是您问题中代码的相关行。

_cars = new Car[size];

这将创建一个包含 size 个元素的数组，但每个元素都是空的。因此 _noOfCars 的目的是告诉您数组 _cars 中有多少 non-null 个元素。因此，在方法 getNewest 中的所有 for 循环中（在 class CarSales 中），您需要遍历数组 [=16= 的所有 non-null 元素] 而不是遍历所有元素。因此每个 for 循环应该是：

for (int i = 0; i < _noOfCars; i++)

因此，方法 addCar（也在 class CarSales 中）需要更新 _noOfCars。这是更正的方法。

public boolean addCar(Car car) {
    if (_noOfCars < _cars.length) {
        _cars[_noOfCars++] = car;
        return true;
    }
    else {
        return false;
    }
}

我假设在方法 getNewest 中，您想 return 从包含所有最新汽车的数组中随机选择一个元素。在下面的代码中，我使用 class ThreadLocalRandom 为数组生成一个随机索引。

public Car getNewest() {
    Car newest = _cars[0];
    int size = 0;
    for (int i = 1; i < _noOfCars; i++)
        if (newest.getYear() < _cars[i].getYear())
            newest = _cars[i];

    for (int i = 0; i < _noOfCars; i++)
        if (newest.getYear() == _cars[i].getYear())
            size++;

    Car[] _new = new Car[size];
    int ndx = 0;
    for (int i = 0; i < _noOfCars; i++)
        if (newest.getYear() == _cars[i].getYear())
            _new[ndx++] = new Car(_cars[i]);

    return _new[ThreadLocalRandom.current().nextInt(0, _new.length)];
}

这是一个完整的例子。由于您没有 post classes Owner 和 Bid 的代码，我为它们做了最少的定义，我还添加了一个 main 方法class Car 从而得到完整的可以编译的程序运行.

import java.util.concurrent.ThreadLocalRandom;

public class Car {
    private Owner _owner; // an object from 1st class
    private String _manufacturer;
    private boolean _airbag;
    private boolean _leasingOrRental;
    private int _km, _seats, _year;
    private int _price;
    private int _LevyPrice;
    private Bid _highestBid;// an object from 2st class

    // Constructor
    public Car(Owner ow,
               String mfr,
               boolean isAirbag,
               boolean leasOrRent,
               int kilNum,
               int seatNum,
               int date,
               int price,
               int levy,
               Bid high) {
        _owner = ow; // new Owner(ow);
        _manufacturer = mfr;
        _airbag = isAirbag;
        _leasingOrRental = leasOrRent;
        _km = kilNum;
        _seats = seatNum;
        _year = date;
        _price = price;
        _LevyPrice = levy;
        _highestBid = high; // new Bid(high);
    }

    // copy constrcutor
    public Car(Car other) {
        _owner = other._owner; // new Owner(other._owner);
        _manufacturer = other._manufacturer;
        _airbag = other._airbag;
        _leasingOrRental = other._leasingOrRental;
        _km = other._km;
        _seats = other._seats;
        _year = other._year;
        _price = other._price;
        _LevyPrice = other._LevyPrice;
        _highestBid = other._highestBid; // new Bid(other._highestBid);
    }

    public Owner getOwner() {
        return _owner; // new Owner(_owner);
    }

    public String getManufacturer() {
        return _manufacturer;
    }

    public boolean getAirbag() {
        return _airbag;
    }

    public boolean getIsleasingOrRental() {
        return _leasingOrRental;
    }

    public int getKm() {
        return _km;
    }

    public int getSeats() {
        return _seats;
    }

    public int getYear() {
        return _year;
    }

    public int getLevyPrice() {
        return _LevyPrice;
    }

    public Bid getHighestBid() {
        return _highestBid; // new Bid(_highestBid);
    }

    public void makeBid(Bid bid) {
        if (_highestBid.getBidPrice() < bid.getBidPrice())
            _highestBid.setBidPrice(bid.getBidPrice());
    }

    public boolean isAttractive() {
        return _airbag == true && _leasingOrRental == true && (_km > 0 && _km < 20000)
                && _year >= 3;
    }

    public boolean fitForFamily(int kids) {
        return _seats - 2 >= kids;
    }

    public boolean overUsedCar() {
        final int KILOMERTES = 12000;

        return _km > KILOMERTES * (2022 - _year);
    }

    public String toString() {
        return "Manufacturer: " + _manufacturer + "\n" + "Year: " + _year + "\n" + "Owner: "
                + _owner.toString() + "\n" + "Highest bid: " + _highestBid.getBidPrice();
    }

    public static void main(String[] args) {
        CarSales carSales = new CarSales(5);
        Car carOne = new Car(new Owner("George"), "mfr", true, true, 0, 5, 2020, 1, 1, new Bid(2));
        carSales.addCar(carOne);
        Car carTwo = new Car(new Owner("May"), "mfr", true, true, 0, 5, 2020, 2, 2, new Bid(4));
        carSales.addCar(carTwo);
        System.out.println(carSales.getNewest());
    }
}

class CarSales {
    private Car[] _cars;
    private int _noOfCars;

    public CarSales(int size) {
        _cars = new Car[size];
        _noOfCars = 0;
    }

    public boolean addCar(Car car) {
        if (_noOfCars < _cars.length) {
            _cars[_noOfCars++] = car;
            return true;
        }
        else {
            return false;
        }
    }

    public Car getNewest() {
        Car newest = _cars[0];
        int size = 0;
        for (int i = 1; i < _noOfCars; i++)
            if (newest.getYear() < _cars[i].getYear())
                newest = _cars[i];

        for (int i = 0; i < _noOfCars; i++)
            if (newest.getYear() == _cars[i].getYear())
                size++;

        Car[] _new = new Car[size];
        int ndx = 0;
        for (int i = 0; i < _noOfCars; i++)
            if (newest.getYear() == _cars[i].getYear())
                _new[ndx++] = new Car(_cars[i]);

        return _new[ThreadLocalRandom.current().nextInt(0, _new.length)];
    }
}

class Bid {
    private double bidPrice;

    public Bid(double price) {
        bidPrice = price;
    }

    public double getBidPrice() {
        return bidPrice;
    }

    public void setBidPrice(double bidPrice) {
        this.bidPrice = bidPrice;
    }
}

class Owner {
    private String name;

    public Owner(String name) {
        this.name = name;
    }

    public String toString() {
        return name;
    }
}

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