Question

首先，我是ArrayList的新手。我有这个程序，SalesPerson对象将遍布全球20个城市。对于每次访问，程序将要求用户输入城市名称，城市规模和邮政编码。这是使用for循环和ArrayList完成的。但是当我想要显示所有城市时，它会打印出奇怪的角色。我可以知道我哪里出错吗？

Below is the sample output.

Enter name of city: Singapore

Enter size of city: Small

Enter postal code: 132115

==

Enter name of city: Indonesia

Enter size of city: Big

Enter postal code: 111222

==

Cities Visited: [travellingapp.City@42a57993, travellingapp.City@75b84c92]

这是我的代码：

TravellingApp.java

public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        SalesPerson s1 = new SalesPerson();

        for(int j=1; j<=20; j++)
        {
            System.out.print("Enter name of city: ");
            String name = sc.nextLine();

            System.out.print("Enter size of city: ");
            String size = sc.nextLine();

            System.out.print("Enter postal code: ");
            int postalCode = sc.nextInt();
            sc.nextLine();

            System.out.println("___________________________________________");



            City c1 = new City(name, size, postalCode);
            s1.addCity(c1);

        }
        System.out.print("Cities Visited: "+ s1.returnListOfCities());

    }

SalesPerson.java（Class）

public class SalesPerson {

    private ArrayList<City>listOfCities = new ArrayList<City>();

    public void addCity(City c1)
    {
        listOfCities.add(c1);
    }

    public ArrayList<City> returnListOfCities()
    {
        return listOfCities;
    }
}

City.java（Class）

public class City {

    private String nameOfCity;
    private String sizeOfCity;
    private int postalCode;

    public City(String nameOfCity, String sizeOfCity, int postalCode)
    {
        this.nameOfCity = nameOfCity;
        this.sizeOfCity = sizeOfCity;
        this.postalCode = postalCode;
    }

    public String getNameOfCity() {
        return nameOfCity;
    }

    public String getSizeOfCity() {
        return sizeOfCity;
    }

    public int getPostalCode() {
        return postalCode;
    }

    public void setNameOfCity(String nameOfCity) {
        this.nameOfCity = nameOfCity;
    }

    public void setSizeOfCity(String sizeOfCity) {
        this.sizeOfCity = sizeOfCity;
    }

    public void setPostalCode(int postalCode) {
        this.postalCode = postalCode;
    }   


}

Answer 1

当您致电require 'fruity' arr = Array.new(1000) { |seed| # seed is used to create the same array on each script run, # hence the same benchmark results will be produced Random.new(seed).rand(1..10).to_s } class Array def difference(other) h = other.each_with_object(Hash.new(0)) { |e,h| h[e] += 1 } reject { |e| h[e] > 0 && h[e] -= 1 } end end compare do _coreyward do arr.reduce(Hash.new(0)) { |counts, value| counts[value] += 1 counts }.max[1] <= 2 end _wayne do arr.group_by(&:itself).none? do |_key, values| values.count > 2 end end _sagarpandya82 do arr.sort_by(&:to_i).each_cons(3).none? { |a,b,c| a == b && b == c } end _tadman do arr.sort.slice_when { |a,b| a != b }.map(&:length).max.to_i <= 2 end _cary do arr.difference(arr.uniq*2).empty? end _akuhn do count = Hash.new(0) arr.none? { |each| (count[each] += 1) > 2 } end _oneneptune do arr.each_with_object(Hash.new(0)) { |element,counts| counts[element] += 1 }.values.max < 3 end _glykyo do arr.uniq.map{ |element| arr.count(element) }.max <= 2 end _vlasiak do arr.none? { |el| arr.count(el) > 2 } end end时，该方法会返回s1.returnListOfCities()个对象的arraylist。 City无法识别此格式。

您可以使用迭代器来迭代Arraylist。

System.out.println()

Answer 2

Java中的每个类都来自Object，它有一个toString()方法，这会返回一个类似你看到的字符串，而System.out.println()方法会使用它，所以如果你没有'在你的课堂上实现它，它将使用Object（多态）中的那个。

像

这样的东西

public String toString(){
   return "City { "+nameOfCity+", " + sizeOfCity +", "+postal code+"}";
}

Arraylist Java Program奇怪的输出

2 个答案: