Question

city.getCityName()和country.getCountry()可行。但是如何使用cityname对象获取country？像country.getCity().getCityName()一样？当country.getCity被调用时，它将返回null。

public class Main {

class Country  {

    private String countryName;
    private City city;

    public String getCountry(){
        return countryName;
    }
    public void setCountry(String countryName){
        this.countryName = countryName;
    }

    public City getCity(){
        return city;
    }
    public void setCity(City city){
        this.city = city;
    }
}

class City {

    private String cityName;

    public String getCityName(){
        return cityName;
    }
    public void setCityName(String cityName) {
        this.cityName = cityName;
    }
}


public static void main(String[] args) {

    City city = new City();
    city.setCityName("Chittoor");

    Country country = new Country();
    country.setCountry("INDIA");

    System.out.println("how to get cityName using country object");
}

}

Answer 1

可能的解决方案可能是这样的：

nums.split(', ')

另一个解决方案是让方法getCity（）返回if(mycountry.getCity() != null){ mycountry.getCity().getCityName(); }。在这种情况下，前面的代码变为：

Optional<City>

您可以找到有关可选here的信息。

Answer 2

您需要使用setCity方法在国家/地区类别中设置城市对象：

public static void main(String[] args) {

City city = new City();
city.setCityName("Chittoor");

Country country = new Country();
country.setCountry("INDIA");
country.setCity(city);//setting the city

System.out.println("how to get cityName using country object");
System.out.println(country.getCity().getCityName());//printing the city
}

}

如何拨打＆＃34;城市名称＆＃34;来自Country对象？

2 个答案: