根据值对 Hashmap 进行排序

给定学生在以学科名称为关键且得分为价值的学科中得分 100 分的分数。我们的任务是根据值（即根据标记）对哈希图进行排序。
例子：

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

解决方案：想法是将条目集存储在列表中，并根据值对列表进行排序。然后从列表中获取值和键并将它们放入新的哈希图中。因此，根据值对新的 hashmap 进行排序。
下面是上述思想的实现：

Java

// 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 sortByValue(HashMap hm)
    {
        // Create a list from elements of HashMap
        List > list =
               new LinkedList >(hm.entrySet());
 
        // Sort the list
        Collections.sort(list, new Comparator >() {
            public int compare(Map.Entry o1,
                               Map.Entry o2)
            {
                return (o1.getValue()).compareTo(o2.getValue());
            }
        });
         
        // put data from sorted list to hashmap
        HashMap temp = new LinkedHashMap();
        for (Map.Entry aa : list) {
            temp.put(aa.getKey(), aa.getValue());
        }
        return temp;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        HashMap hm = new HashMap();
 
        // 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 hm1 = sortByValue(hm);
 
        // print the sorted hashmap
        for (Map.Entry en : hm1.entrySet()) {
            System.out.println("Key = " + en.getKey() +
                          ", Value = " + en.getValue());
        }
    }
}

输出

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

使用Java 8 Lambda

在这里，我们将更改排序方式，并使用 lambda 表达式进行排序。逻辑是一样的，甚至我们也传递了比较器对象，但只使用了 lambda。

下面是上述方法的实现：

Java

// Java program to sort hashmap by values
import java.lang.*;
import java.util.*;
 
public class GFG {
 
    // function to sort hashmap by values
    public static HashMap
    sortByValue(HashMap hm)
    {
        // Create a list from elements of HashMap
        List > list
            = new LinkedList >(
                hm.entrySet());
 
        // Sort the list using lambda expression
        Collections.sort(
            list,
            (i1,
             i2) -> i1.getValue().compareTo(i2.getValue()));
 
        // put data from sorted list to hashmap
        HashMap temp
            = new LinkedHashMap();
        for (Map.Entry aa : list) {
            temp.put(aa.getKey(), aa.getValue());
        }
        return temp;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        HashMap hm
            = new HashMap();
 
        // 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 hm1 = sortByValue(hm);
 
        // print the sorted hashmap
        for (Map.Entry en :
             hm1.entrySet()) {
            System.out.println("Key = " + en.getKey()
                               + ", Value = "
                               + en.getValue());
        }
    }
}

输出

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

在Java 8 中使用流

在这里，我们将使用流对地图进行排序。我们将使用stream()方法获取 entrySet 的流，然后使用 sorted() 方法中的 lambda 表达式对流进行排序，最后，我们将使用 toMap() 将其转换为映射 方法。在 toMap() 方法中，我们使用LinkedHashMap::new方法引用来保留地图的排序顺序。

Java

// Java program to sort hashmap by values
import static java.util.stream.Collectors.*;
 
import java.lang.*;
import java.util.*;
import java.util.stream.*;
import java.util.stream.Collectors;
public class gfg3 {
 
    // function to sort hashmap by values
    public static HashMap
    sortByValue(HashMap hm)
    {
        HashMap temp
            = hm.entrySet()
                  .stream()
                  .sorted((i1, i2)
                              -> i1.getValue().compareTo(
                                  i2.getValue()))
                  .collect(Collectors.toMap(
                      Map.Entry::getKey,
                      Map.Entry::getValue,
                      (e1, e2) -> e1, LinkedHashMap::new));
 
        return temp;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        HashMap hm
            = new HashMap();
 
        // 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 hm1 = sortByValue(hm);
 
        // print the sorted hashmap
        for (Map.Entry en :
             hm1.entrySet()) {
            System.out.println("Key = " + en.getKey()
                               + ", Value = "
                               + en.getValue());
        }
    }
}

输出

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