Geeks For Geeks对HashMap按值排序

Input : Key = Math, Value = 98
    Key = Data Structure, Value = 85
    Key = Database, Value = 91
    Key = Java, Value = 95
    Key = Operating System, Value = 79
    Key = Networking, Value = 80

Output : Key = Operating System, Value = 79
         Key = Networking, Value = 80
         Key = Data Structure, Value = 85
         Key = Database, Value = 91
         Key = Java, Value = 95
         Key = Math, Value = 98
Solution: The idea is to store the entry set in a list and sort the list on the basis of values. Then fetch values and keys from the list and put them in a new hashmap. Thus, a new hashmap is sorted according to values.
Below is the implementation of the above idea: 




// Java program to sort hashmap by values
import java.util.*;
import java.lang.*;
 
public class GFG {
 
    // function to sort hashmap by values
    public static HashMap<String, Integer> sortByValue(HashMap<String, Integer> hm)
    {
        // Create a list from elements of HashMap
        List<Map.Entry<String, Integer> > list =
               new LinkedList<Map.Entry<String, Integer> >(hm.entrySet());
 
        // Sort the list
        Collections.sort(list, new Comparator<Map.Entry<String, Integer> >() {
            public int compare(Map.Entry<String, Integer> o1,
                               Map.Entry<String, Integer> o2)
            {
                return (o1.getValue()).compareTo(o2.getValue());
            }
        });
         
        // put data from sorted list to hashmap
        HashMap<String, Integer> temp = new LinkedHashMap<String, Integer>();
        for (Map.Entry<String, Integer> aa : list) {
            temp.put(aa.getKey(), aa.getValue());
        }
        return temp;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        HashMap<String, Integer> hm = new HashMap<String, Integer>();
 
        // enter data into hashmap
        hm.put("Math", 98);
        hm.put("Data Structure", 85);
        hm.put("Database", 91);
        hm.put("Java", 95);
        hm.put("Operating System", 79);
        hm.put("Networking", 80);
        Map<String, Integer> hm1 = sortByValue(hm);
 
        // print the sorted hashmap
        for (Map.Entry<String, Integer> en : hm1.entrySet()) {
            System.out.println("Key = " + en.getKey() +
                          ", Value = " + en.getValue());
        }
    }
}
Output
Key = Operating System, Value = 79
Key = Networking, Value = 80
Key = Data Structure, Value = 85
Key = Database, Value = 91
Key = Java, Value = 95
Key = Math, Value = 98

这可以用java8非常容易地实现

public static LinkedHashMap<Integer, String> sortByValue(HashMap<Integer, String> map) {

        List<Map.Entry<Integer, String>> list = new ArrayList<>(map.entrySet());
        list.sort(Map.Entry.comparingByValue());
        LinkedHashMap<Integer, String> sortedMap = new LinkedHashMap<>();
        list.forEach(e -> sortedMap.put(e.getKey(), e.getValue()));
        return sortedMap;
    }

最好的方法是将HashMap转换为TreeMap。TreeMap自己排序键。如果您希望对值进行排序，则可以快速修复，如果您的值不重复，则可以使用键切换值。

给定的地图

   Map<String, Integer> wordCounts = new HashMap<>();
    wordCounts.put("USA", 100);
    wordCounts.put("jobs", 200);
    wordCounts.put("software", 50);
    wordCounts.put("technology", 70);
    wordCounts.put("opportunity", 200);

根据值按升序对地图进行排序

Map<String,Integer>  sortedMap =  wordCounts.entrySet().
                                                stream().
                                                sorted(Map.Entry.comparingByValue()).
        collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
    System.out.println(sortedMap);
    

根据值按降序排序地图

Map<String,Integer>  sortedMapReverseOrder =  wordCounts.entrySet().
            stream().
            sorted(Map.Entry.comparingByValue(Comparator.reverseOrder())).
            collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
    System.out.println(sortedMapReverseOrder);

输出：

{软件=50，技术=70，美国=100，工作=200，机会=200}

｛工作岗位=200，机会=200，美国=100，技术=70，软件=50｝

因为地图是无序的要对其进行排序，我们可以执行以下操作

Map<String, String> map= new TreeMap<String, String>(unsortMap);

您应该注意，与哈希映射不同，树映射保证其元素将按升序键排序。

在TreeMap中，键按自然顺序排序。例如，如果您对数字进行排序，（注意4的排序）

{0=0, 10=10, 20=20, 30=30, 4=4, 50=50, 60=60, 70=70}

要解决这个问题，在Java8中，首先检查字符串长度，然后进行比较。

Map<String, String> sortedMap = new TreeMap<>Comparator.comparingInt(String::length)
.thenComparing(Function.identity()));

{0=0, 4=4, 10=10, 20=20, 30=30, 50=50, 60=60, 70=70}