Java 根据数值对HashMap进行排序

2023-02-28 15:39| 来源: 网络整理| 查看: 265

给出一个学生在100个科目中的分数，其中科目的名称是关键，分数是值。我们的任务是根据数值对HashMap进行排序，即根据分数进行排序。

示例：

输入 : 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

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

解决方案：我们的想法是将条目集存储在一个列表中，并根据数值对列表进行排序。然后从列表中获取值和键，并将其放入一个新的哈希玛。这样，一个新的HashMap就根据值进行了排序。以下是上述想法的实现：

// 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 Lambdas

这里我们将改变我们的排序方式，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，但只是使用lambda。

下面是上述方法的实现。

// 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

这里我们将使用流来对地图进行排序。我们将使用 stream() 方法来获取entrySet的流，然后在sorted()方法中使用lambda表达式来对流进行排序，最后，我们将使用toMap() 方法将其转换成map。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 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

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