如何阻止 Java 代码重复 object 数组的最后一个值？

Question

我正在和一个朋友一起做一个项目；我们正在尝试创建一个飞机项目，使用 Passenger class 表示乘客，Airplane class 添加乘客并创建飞机，以及 driver class。我们运行遇到一个问题，当我们将所有乘客添加到飞机上并打印飞机的所有详细信息时，打印值仅捕获最后一位乘客的信息。我们正在努力为每一位乘客做到这一点。这是代码：

乘客

public class Passenger {

    private String name;
    private int  birthYear;
    private double weight;
    private char gender;
    private int numCarryOn;

    //Default constructor
    public Passenger(){
        name = "";
        birthYear = 1900;
        weight = 0.0;
        gender = 'u';
        numCarryOn = 0;
    }

    //Alt default constructor
    public Passenger(String newName, int newBirthYear, double newWeight, char newGend, int newNumCarryOn){

        this.setName(newName);
        this.setBirthYear(newBirthYear);
        this.setWeight(newWeight);
        this.setGender(newGend);
        this.setNumCarryOn(newNumCarryOn);
    }

    //Calculate age
    public int calculateAge(int currentYear){

        int age = 0;

        if (currentYear < birthYear){
            return -1;
        }
        else {
            age = currentYear - birthYear;
        }

        return age;
    }

    //Gain weight
    public void gainWeight(){
        weight += 1;
    }

    //Gain weight based on input
    public void gainWeight(double pounds){

        if (weight > 0){
            weight = weight + pounds;
        }

    }

    //Get birthYear
    public int getBirthYear(){
        return birthYear;
    }

    //Get gender
    public char getGender(){
        return gender;
    }

    //Get name
    public String getName(){
        return name;
    }

    //Get weight
    public double getWeight(){
        return weight;
    }

    //Get numCarryOn
    public int getNumCarryOn(){
        return numCarryOn;
    }

    //isFemale
    public boolean isFemale(){

        if (gender == 'f'){
            return true;
        }
        else {
            return false;
        }
    }

    //isMale
    public boolean isMale(){
        if (gender == 'm'){
            return true;
        }
        else {
            return false;

        }
    }

    //loseWeight
    public void loseWeight(){

        if (weight > 0){
            weight -= 1;
        }

    }

    //lose weight by value
    public void loseWeight(double weight2lose){

        if (weight - weight2lose >= 0){
            weight -= weight2lose;
        }

    }

    //print
    public void printDetails(){

        System.out.printf("Name: %20s | Year of Birth: %4d | Weight: %10.2f | Gender: %c | NumCarryOn: %2d\n", name, birthYear, weight, gender, numCarryOn);

    }

    //setGender
    public void setGender(char newGender){

        if (newGender == 'f' || newGender == 'm') {
            this.gender = newGender;
        } else {
            this.gender = 'u';
        }
    }

    //setName
    public void setName(String newName){
        name = newName;
    }

    //setBirthYear
    public void setBirthYear(int newBY){
        birthYear = newBY;
    }

    //setWeight
    public void setWeight(double newWeight){

        if (newWeight < 0){
            weight = -1;

        }
        else {
            weight = newWeight;
        }

    }

    //setNumCarryOn
    public void setNumCarryOn(int newNumCarryOn){

        if (newNumCarryOn < 0){
            numCarryOn = 0;

        }
        else if (newNumCarryOn > 2){
            numCarryOn = 2;
        }
        else {
            numCarryOn = newNumCarryOn;
        }
    }
}

飞机


public class Airplane {

    private Passenger[] passengers;
    private String airplaneName;
    private int numPassengers;
    public int count = 0;

    //default constructor
    public Airplane(){

        airplaneName = "";
        passengers = new Passenger[100];
        numPassengers = 0;
    }

    //default constructor with String input
    public Airplane(String otherairplaneName){

        airplaneName = otherairplaneName;
        passengers = new Passenger[100];
        numPassengers = 0;

    }

    //default constructor with int input
    public Airplane(int otherArraySize){

        airplaneName = "";

        if (otherArraySize < 0){
            otherArraySize = 0;
        }
        passengers = new Passenger[otherArraySize];


        numPassengers = 0;

    }

    //default constructor with String and int input
    public Airplane(String otherAirplaneName, int otherArraySize){

        airplaneName = otherAirplaneName;

        if (otherArraySize < 0){
            otherArraySize = 0;
        }

        passengers = new Passenger[otherArraySize];


        numPassengers = 0;

    }

    //add a passenger
    public void addPassenger(Passenger a){

        for (int i = 0; i < passengers.length; i++){


           passengers[i] = a;



        }
    }


    //resize array for new passengers
    private void resizePassengerArray(){

        passengers = new Passenger[passengers.length * 2];

    }

    //get a passenger
    public Passenger getPassenger(int passengerIndex){

        return passengers[passengerIndex];
    }

    //getNumPassengers
    public int getNumPassengers() {

       return count;
    }

    //getFirstPassenger
    public Passenger getFirstPassenger(){

        return passengers[0];
    }

    //getLastPassenger
    public Passenger getLastPassenger(){

        return passengers[passengers.length - 1];
    }

    //getPassengers**
    public Passenger[] getPassengers(){

        return passengers;
    }

    //setAirplaneName
    public void setAirplaneName(String newAirplaneName){

        airplaneName = newAirplaneName;
    }

    //printAllDetails
    public void printAllDetails(){

        System.out.printf("AirplaneName: %20s | Number of Passengers: %4d | Airplane Size: %4d\n", airplaneName, count, passengers.length);

        for (int i = 0; i < count; i++){
            System.out.printf("Name: %20s | Year of Birth: %4d | Weight: %10.2f | Gender: %c\n", passengers[i].getName(), passengers[i].getBirthYear(), passengers[i].getWeight(), passengers[i].getGender());

        }
    }

    //removePassenger
    public Passenger removePassenger(int passengerIndex){

        if (passengerIndex != passengers.length - 1){

            for (int i = passengerIndex; i < passengers.length - 1; i++){

                passengers[i] = passengers[i+1];

            }
        }

        return passengers[passengerIndex];
    }

    //remove all passengers
    public void removeAllPassengers(){

       passengers = new Passenger[100];
    }

    //total weight passengers
    public double getTotalWeightOfAllPassengers(){

        double weight = 0.0;

        for (int i = 0; i < passengers.length; i++){
            weight += passengers[i].getWeight();
        }

        return weight;
    }

    //avg weight passengers
    public double getAverageWeightOfAllPassengers(){

        double avg = this.getTotalWeightOfAllPassengers() / numPassengers;

        return avg;
    }

    //num elements above weight
    public int getNumberOfPassengersAboveWeight(double weight){

        int sum = 0;

        for (int i = 0; i < passengers.length; i++){

            if (passengers[i].getWeight() > weight){
                sum += 1;
            }

        }

        return sum;
    }

    //num elements below weight
    public int getNumberOfPassengersBelowWeight(double weight){

        int sum = 0;

        for (int i = 0; i < passengers.length; i++){

            if (passengers[i].getWeight() < weight){
                sum += 1;
            }

        }

        return sum;
    }

    //increase weight of passengers
    public void increaseWeightOfAllPassengers(){

        for (int i = 0; i < passengers.length; i++){
            passengers[i].gainWeight();
        }

    }

    //increase weight of passengers with weight input
    public void increaseWeightOfAllPassengers(double increaseAmount){

        for (int i = 0; i < passengers.length; i++){
            passengers[i].gainWeight(increaseAmount);
        }

    }



}

Driver

public class RunAirplane {
    public static void main(String[] args) {
        Airplane a1 = new Airplane("Flight 1", 100);
        Passenger p1 = new Passenger("Albert", 1879, 198.5, 'm', 2);
        Passenger p2 = new Passenger("Grace", 1906, 105, 'f', 1);
        Passenger p3 = new Passenger("Tim", 1955, 216.3, 'm', 2);
        Passenger p4 = new Passenger("Steve", 1955, 160, 'm', 2);
        Passenger p5 = new Passenger("Sergey", 1973, 165.35, 'm', 1);

        a1.addPassenger(p1);
        a1.count += 1;
        a1.addPassenger(p2);
        a1.count += 1;
        a1.addPassenger(p3);
        a1.count += 1;
        a1.addPassenger(p4);
        a1.count += 1;
        a1.addPassenger(p5);
        a1.count += 1;
        a1.printAllDetails();

        //How it should work starting with name
        System.out.println(p1.getName());
        System.out.println(p2.getName());

    }
}

下面是错误代码的截图： https://imgur.com/TGc0FQa

Answer 1

addPassenger() 方法正在覆盖数组中的每个元素：

public void addPassenger(Passenger a){
    for (int i = 0; i < passengers.length; i++){
       passengers[i] = a;
    }
}

它应该只设置下一个可用索引，恰好是 count:

public void addPassenger(Passenger a){
    passengers[count++] = a;
}

这也为您提供了更好的封装，因为您不必在外部公开和增加 count。

Answer 2

这个

    public void addPassenger(Passenger a){

        for (int i = 0; i < passengers.length; i++){


           passengers[i] = a;



        }
    }

每次 Passenger Array 充满同一个 Passenger 时产生。也许这可以解决问题。


public void addPassenger(Passenger a){

        for (int i = 0; i < passengers.length; i++){

          if((passengers[i-1] !=null)&&((passengers[i] ==null))
          { passengers[i] = a; }




        }
    }

更好的实现方式可能是 ArrayList

飞机


public class Airplane {

    private ArrayList<Passenger> passengers;
    private String airplaneName;
    private int numPassengers;
    public int count = 0;

    //default constructor
    public Airplane(){

        airplaneName = "";
        passengers = new ArrayList();
        numPassengers = 0;
    }

    //default constructor with String input
    public Airplane(String otherairplaneName){

        airplaneName = otherairplaneName;
        passengers = new ArrayList();
        numPassengers = 0;

    }

    

    //default constructor with String and int input
    public Airplane(String otherAirplaneName){

        airplaneName = otherAirplaneName;


        passengers = new ArrayList();


        numPassengers = 0;

    }

    //add a passenger
    public void addPassenger(Passenger a){
        
        passengers.add(a);
      
    }


    //get a passenger
    public Passenger getPassenger(int passengerIndex){

        return passengers[passengerIndex];
    }

    //getNumPassengers
    public int getNumPassengers() {

       return count;
    }

    //getFirstPassenger
    public Passenger getFirstPassenger(){

        return passengers.get(0);
    }

    //getLastPassenger
    public Passenger getLastPassenger(){

        return passengers.get(passengers.size() - 1);
    }

    //getPassengers**
    public ArrayList<Passenger> getPassengers(){

        return passengers;
    }

    //setAirplaneName
    public void setAirplaneName(String newAirplaneName){

        airplaneName = newAirplaneName;
    }

    //printAllDetails
    public void printAllDetails(){

        System.out.printf("AirplaneName: %20s | Number of Passengers: %4d | Airplane Size: %4d\n", airplaneName, count, passengers.size());

        for (int i = 0; i < count; i++){
            System.out.printf("Name: %20s | Year of Birth: %4d | Weight: %10.2f | Gender: %c\n", passengers.get(i).getName(), passengers[i].get(i).getBirthYear(), passengers[i].get(i).getWeight(), passengers[i].get(i).getGender());

        }
    }

    //removePassenger
    public Passenger removePassenger(int passengerIndex){

            passengers.remove(passengerIndex);

        return passengers.get(passengerIndex);
    }

    //remove all passengers
    public void removeAllPassengers(){

       passengers = new ArrayList();
    }

    //total weight passengers
    public double getTotalWeightOfAllPassengers(){

        double weight = 0.0;

        for (int i = 0; i < passengers.size(); i++){
            weight += passengers.get(i).getWeight();
        }

        return weight;
    }

    //avg weight passengers
    public double getAverageWeightOfAllPassengers(){

        double avg = this.getTotalWeightOfAllPassengers() / numPassengers;

        return avg;
    }

    //num elements above weight
    public int getNumberOfPassengersAboveWeight(double weight){

        int sum = 0;

        for (int i = 0; i < passengers.size(); i++){

            if (passengers.get(i).getWeight() > weight){
                sum += 1;
            }

        }

        return sum;
    }

    //num elements below weight
    public int getNumberOfPassengersBelowWeight(double weight){

        int sum = 0;

        for (int i = 0; i < passengers.size(); i++){

            if (passengers.get(i).getWeight() < weight){
                sum += 1;
            }

        }

        return sum;
    }

    //increase weight of passengers
    public void increaseWeightOfAllPassengers(){

        for (int i = 0; i < passengers.size(); i++){
            passengers.get(i).gainWeight();
        }

    }

    //increase weight of passengers with weight input
    public void increaseWeightOfAllPassengers(double increaseAmount){

        for (int i = 0; i < passengers.size(); i++){
            passengers.get(i).gainWeight(increaseAmount);
        }

    }



}

Answer 3

问题出在方法 addPassenger 中。您总是替换第一个元素。

你可以这样修复：

public void addPassenger(Passenger a){
    passengers[count] = a;
    count++
}

为了更好地实现，您可以删除count并使用numPassengers。

因此方法变为：

public void addPassenger(Passenger a){
    passengers[numPassengers] = a;
    numPassengers++
}

和主要 class:

public class RunAirplane {
    public static void main(String[] args) {
        Airplane a1 = new Airplane("Flight 1", 100);
        Passenger p1 = new Passenger("Albert", 1879, 198.5, 'm', 2);
        Passenger p2 = new Passenger("Grace", 1906, 105, 'f', 1);
        Passenger p3 = new Passenger("Tim", 1955, 216.3, 'm', 2);
        Passenger p4 = new Passenger("Steve", 1955, 160, 'm', 2);
        Passenger p5 = new Passenger("Sergey", 1973, 165.35, 'm', 1);

        a1.addPassenger(p1);
        a1.addPassenger(p2);
        a1.addPassenger(p3);
        a1.addPassenger(p4);
        a1.addPassenger(p5);
        a1.printAllDetails();

        //How it should work starting with name
        System.out.println(p1.getName());
        System.out.println(p2.getName());

    }
}

为了实现最佳效果，您可以使用 List 而不是字段 passengers:

的数组

private List<Passenger> passengers;

public Airplane(){
    airplaneName = "";
    passengers = new ArrayList<>();
}

public void addPassenger(Passenger a){
    passengers.add(a);
}

您可以删除 numPassengers 并使用 size:

public int getNumPassengers() {
   return passengers.size();
}

如何阻止 Java 代码重复 object 数组的最后一个值？

How to stop Java code from repeating last value of object array?

java

oop