how to connect 2 list with each other?-CodePudding

I want to make an address system, so I have to make an ArrayList for the county and another for the district. Still, the problem is how can I make each element from the first array have an array on its own in the 2nd array? for example if int the 1st array ("Istanbul, bursa") and for 2nd array i want to give Istanbul ("avcilar, fatih") and for bursa i want to give("zaytin, elma")

import java.util.ArrayList;

public class Address {
    ArrayList<String> county=new ArrayList();
    ArrayList<String> district=new ArrayList();
}

CodePudding user response：

you described a one-to-many relation between country and district. the best way to describe this relation in Java is to have a Country class with list of districts, and then you can have a list of Country instances.

public class Country {
    ArrayList<String> districts = new ArrayList();
}

public class Address {
    ArrayList<Country> countries = new ArrayList();
}

note that by convention, variable names for lists is in plural

now you can create a country. fill its list of districts. repeat for every country and put instances in countries of address

Country turkey = new Country();
turkey.districts.add("Istanbul");
turkey.districts.add("another city");

CodePudding user response：

The data model should be refactored to reflect a hierarchy between "counties" or rather provinces and districts where a county/province has at least a name and a list of related districts. In a simple model a district can be represented with just a name, but generally it may also contain other attributes (e.g., population, area, list of cities/towns/villages, etc.):

public class County {
    private String name;
    private List<District> districts;

    public County(String name, List<District> districts) {
        this.name = name;
        this.districts = districts;
    }
//  ... getters
}

public class District {
    private String name;
    // other details/attributes if needed
    public District(String name) {
        this.name = name;
    }
}

Then assuming there's a method to convert a list of strings representing district names

public static List<District> districts(List<String> names) {
    return names.stream().map(District::new).collect(Collectors.toList());
}

The list of counties/provinces may be populated as follows:

List<Country> counties = Arrays.asList(
    new County("Istanbul", districts("Adalar", "Avcılar", "Fatih")),
    new County("Bursa", districts("Gürsu", "Kestel", "Yıldırım"))
);