关于java：根据键和值对地图进行排序

sorting a map on the basis of key and value

本问题已经有最佳答案，请猛点这里访问。

我开发了下面的代码，我们可以根据键和值对Hash Map进行排序。

主要的逻辑是，我们可以对Map进行排序，可以是HashMap或Hashtable通过将密钥复制到List中，而不是使用Collections.sort()方法对List进行排序，在这里，您可以根据要按自定义顺序还是自然顺序进行排序，使用Comparator或Comparable。对键的List进行排序后，我们可以创建另一个映射，尤其是LinkedHashMap以按排序顺序插入键。LinkedHashMap将保持插入键的顺序，结果是基于键的排序映射

我的问题是，如果你校准，请建议我其他更好的方法或任何改进，你们可以建议。

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public class MapSortingExample {

public static void main(String args[]) {

//creating Hashtable for sorting
Map<String, Integer> olympic2012 = new HashMap<String, Integer>();

olympic2012.put("England", 3);
olympic2012.put("USA", 1);
olympic2012.put("China", 2);
olympic2012.put("Russia", 4);
//olympic2012.put("Australia", 4); //adding duplicate value

//printing hashtable without sorting
System.out.println("Unsorted Map in Java :" + olympic2012);

//sorting Map e.g. HashMap, Hashtable by keys in Java
Map<String, Integer> sorted = sortByKeys(olympic2012);
System.out.println("Sorted Map in Java by key:" + sorted);

//sorting Map like Hashtable and HashMap by values in Java
sorted = sortByValues(olympic2012);
System.out.println("Sorted Map in Java by values:" + sorted);

//Sorting Map in Java by keys using TreeMap
Map<String, Integer> sortedMapByKeys = new TreeMap<String,Integer>();
sortedMapByKeys.putAll(olympic2012);
System.out.println("Sorted Map in Java by key using TreeMap :" + sortedMapByKeys);

//Sorting Map by keys in Java using Google Collections (Guava)
//Main benefit is you can specify any ordering like natural or toString or arbitrary
Map<String, Integer> sortingUsingGuava = Maps.newTreeMap(Ordering.natural());
sortingUsingGuava.putAll(olympic2012);
System.out.println("Example to sort Map in Java using Guava :" + sortingUsingGuava);

}

/*
* Paramterized method to sort Map e.g. HashMap or Hashtable in Java
* throw NullPointerException if Map contains null key
*/
public static <K extends Comparable,V extends Comparable> Map<K,V> sortByKeys(Map<K,V> map){
List<K> keys = new LinkedList<K>(map.keySet());
Collections.sort(keys);

//LinkedHashMap will keep the keys in the order they are inserted
//which is currently sorted on natural ordering
Map<K,V> sortedMap = new LinkedHashMap<K,V>();
for(K key: keys){
sortedMap.put(key, map.get(key));
}

return sortedMap;
}

/*
* Java method to sort Map in Java by value e.g. HashMap or Hashtable
* throw NullPointerException if Map contains null values
* It also sort values even if they are duplicates
*/
public static <K extends Comparable,V extends Comparable> Map<K,V> sortByValues(Map<K,V> map){
List<Map.Entry<K,V>> entries = new LinkedList<Map.Entry<K,V>>(map.entrySet());

Collections.sort(entries, new Comparator<Map.Entry<K,V>>() {

@Override
public int compare(Entry<K, V> o1, Entry<K, V> o2) {
return o1.getValue().compareTo(o2.getValue());
}
});

//LinkedHashMap will keep the keys in the order they are inserted
//which is currently sorted on natural ordering
Map<K,V> sortedMap = new LinkedHashMap<K,V>();

for(Map.Entry<K,V> entry: entries){
sortedMap.put(entry.getKey(), entry.getValue());
}

return sortedMap;
}

}

输出将是..

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Unsorted Map in Java : {USA=1, England=3, Russia=4, China=2}
Sorted Map in Java by key: {China=2, England=3, Russia=4, USA=1}
Sorted Map in Java by values: {USA=1, China=2, England=3, Russia=4}
Sorted Map in Java by key using TreeMap : {China=2, England=3, Russia=4, USA=1}
Example to sort Map in Java using Guava : {China=2, England=3, Russia=4, USA=1}

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