java - 如何将对象按字母顺序插入到ArrayList中？

Question

这似乎与这里的其他问题类似，但它有所不同，因为我不想对预先存在的 ArrayList 进行排序。我正在寻找插入对象，当我插入对象时，我检查它是否按字母顺序排列。如果不是，我继续直到 arraylist 的末尾，然后将其添加到 ArrayList 的末尾。

我已有的代码似乎有问题，因为当我运行测试代码时，我的 toString() 方法似乎没有打印任何对象。

import java.util.ArrayList;
import java.util.List;

public class CityDB {
    ArrayList<City>cityList = new ArrayList<>();


    public ArrayList<City> getCityList(){
        return cityList;
    }

    public void addCity(City city){
        for (int i=0; i<cityList.size();i++){
            if (cityList.get(i).getName().toLowerCase().compareTo(city.getName().toLowerCase()) == 0){
                //city is the same as one of the cities in the list (case insensitive)
                //quit the loop (does not store two cities with same name)
                break;
            }else if (cityList.get(i).getName().toLowerCase().compareTo(city.getName().toLowerCase()) <0 && cityList.get(i+1).getName().toLowerCase().compareTo(city.getName().toLowerCase()) >0){
                //city before is lexicographically lesser but city after is lexicographically more (case insensitive)
                cityList.add(i+1, city);
                //inserts at i+1, which is after the lexicographically smaller city, but is before the city which is lexicographically larger
                break;
            }else if (i == cityList.size()-1){
                cityList.add(city);
            }
        }
    }
}

Answer 1

当您添加第一个城市时，大小为零。你的循环不会被执行。所提供的条件已被破坏

for (int i=0; i<cityList.size();i++){
    if (cityList.get(i).getName().toLowerCase().compareTo(city.getName().toLowerCase()) == 0){
        //city is the same as one of the cities in the list (case insensitive)
        //quit the loop (does not store two cities with same name)
        return;
    }else if (cityList.get(i).getName().toLowerCase().compareTo(city.getName().toLowerCase()) <0 && cityList.get(i+1).getName().toLowerCase().compareTo(city.getName().toLowerCase()) >0){
            //city before is lexicographically lesser but city after is lexicographically more (case insensitive)
            cityList.add(i+1, city);
            //inserts at i+1, which is after the lexicographically smaller city, but is before the city which is lexicographically larger
            return;
    }

}
cityList.add(city);

然后您需要修复循环中的条件。第一个条件可以，但考虑第二个条件:

cityList.get(i).getName().toLowerCase().compareTo(city.getName().toLowerCase()) <0 
&& 
cityList.get(i+1).getName().toLowerCase().compareTo(city.getName().toLowerCase()) > 0

这不需要分为两部分。首先检查它是否小于当前索引 i，如果小于则将其添加到该索引处。 不检查i+1