如何在另一个模型类中创建列表

Question

我有两个bean类--乡村和城市。我需要在乡村班保留城市名单。另外，当我设置城市信息时，我需要设置国家名称，所以在城市类中也需要国家。怎么做？以下是代码：

country.java

 public class Country {

private String name;
private String about;
 ArrayList<City> cities;

public Country()
{
    cities = new ArrayList<City>();
}

public Country(String name, String about)
{
    this.name= name;
    this.about = about;
}


public int getNoOfCities()
{
    return cities.size();
}


public long getNoOfCitizens()
{ Long aPop= 0L;
    //Long aPopulation = cities.get 
    for(City aCity: cities)
    {
       aPop += aCity.getPopulation();
    }
    return aPop;
}



public String getName(){
    return name;

} 
public String getAbout(){
    return about;
}
}

 public class City {

    private String name;
    private String about;
    private Long population;

    public City(String name, String about, Long population)
    {
        this.name= name;
        this.name = about;
        this.population = population;


    }
    public String getName(){
        return name;

    } 
    public String getAbout(){
        return about;

    } 
    public Long getPopulation(){
        return population;
    } 
 }

Answer 1

我不确定我是否完全理解这个问题，但我能想到的最简单的事情是在城市中添加乡村的提法。如果你仔细想想，这是完全有道理的--每个城市都位于一个国家，所以没有国家的城市是不可能的。

public class City {

private String name;
private String about;
private Long population;
private Country country;

public City(String name, String about, Long population, Country country)
{
    this.name= name;
    this.name = about;
    this.population = population;
    this.country=country;
    country.addCity(this);
}