java 在 Hashmap<String, Object> 中对 Object 的值进行排序
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Sort the Object's value inside the Hashmap<String, Object>
提问by newbie
I want to sort an Hashmap by the object's value. In this case, by country code.
我想按对象的值对 Hashmap 进行排序。在这种情况下，按国家/地区代码。
KEY OBJECT
String LoyaltyCountry
- country name
- country code
- country loc
My code is as follows:
我的代码如下：
public static HashMap<String, LoyaltyCountry> loyaltyCountrySortMap(HashMap<String, LoyaltyCountry> loyaltyCountryMap) {
if (loyaltyCountryMap != null) {
List keys = new ArrayList();
keys.addAll(loyaltyCountryMap.keySet());
Collections.sort(keys, new Comparator<LoyaltyCountry>() {
public int compare(LoyaltyCountry o1, LoyaltyCountry o2) {
return o1.getCountryName().compareTo(o2.getCountryName());
}
});
}
return loyaltyCountryMap;
}
How can I do this correctly?
我怎样才能正确地做到这一点？
回答by Sarel Botha
Here is a method that returns a Set containing the Map.Entry items sorted by their value.
这是一个返回包含按其值排序的 Map.Entry 项的 Set 的方法。
public static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> entriesSortedByValues(Map<K, V> map) {
SortedSet<Map.Entry<K, V>> sortedEntries = new TreeSet<Map.Entry<K, V>>(
new Comparator<Map.Entry<K, V>>() {
@Override
public int compare(Map.Entry<K, V> e1, Map.Entry<K, V> e2) {
return e1.getValue().compareTo(e2.getValue());
}
});
sortedEntries.addAll(map.entrySet());
return sortedEntries;
}
回答by trutheality
Create a Comparator<Map.Entry<String,LoyaltyCountry>>, get the Map.entrySet(), put it into a List<Map.Entry<String,LoyaltyCountry>>and sort it.
创建 a Comparator<Map.Entry<String,LoyaltyCountry>>，获取Map.entrySet()，将其放入 aList<Map.Entry<String,LoyaltyCountry>>并对其进行排序。
Clarification: You say you want to sort the HashMapby values -- that isn't going to happen. A HashMapis an unsorted implementation of a Map. Moreover, the sorted implementations of Mapall sort on keys, so even a TreeMapwon't help you.
澄清：你说你想HashMap按值排序- 这不会发生。AHashMap是 a 的未排序实现Map。此外，Map所有排序键的排序实现，所以即使 aTreeMap也无济于事。
The closest you can come to it (short of making your own map implementation) is produce a list of the map entries, which is what I described how to do above.
最接近它的方法（没有制作自己的地图实现）是生成地图条目的列表，这就是我在上面描述的如何执行的操作。
回答by Alexander Pogrebnyak
You can't sort HashMap.
你不能排序HashMap。
Looks like you want to return an ordered list of map's values, sorted by country name.
看起来您想要返回按国家/地区名称排序的地图值的有序列表。
For that change return type of your method to List, e.g
对于将您的方法的返回类型更改为 List，例如
public static List<LoyaltyCountry> loyaltyCountrySortMap(
HashMap<String, LoyaltyCountry> loyaltyCountryMap
)
{
if (loyaltyCountryMap != null) {
List<LoyaltyCountry> values = new ArrayList();
values.addAll(loyaltyCountryMap.values());
Collections.sort(values, new Comparator<LoyaltyCountry>() {
public int compare(LoyaltyCountry o1, LoyaltyCountry o2) {
return o1.getCountryName().compareTo(o2.getCountryName());
}
});
return values;
}
return null;
}
