Java HashMap根据键对进行排序

浅浅的花香味﹌ 2023-09-23 23:29 159阅读 0赞

> HashMap根据键对进行排序有三种方法  
> 1)使用 TreeMap（putAll 方法）  
> 2)使用 TreeMap（构造函数）  
> 3)使用数组列表

# 1.使用 TreeMap（putAll 方法） #

> 使用 TreeMap（putAll 方法） 思路是把HashMap的所有数据放到一个TreeMap中。 TreeMap 遵循基于红黑树的实现。映射根据其键的自然顺序进行排序。

public class Test2 {
        
        public static void main(String[] args) throws Exception {
        
            int [] nums={
        3,4,2,1};
            String[]h= {
        "a","c","d","e"};
    
            Map<Integer,String> map = new HashMap<Integer,String>();
            for(int i=0;i<nums.length;i++){
        
                map.put(nums[i],h[i]);
            }
    
            TreeMap<Integer, String> sorted = new TreeMap<>();
    
            //TreeMap 存储 HashMap 的值
            sorted.putAll(map);
    
            // 显示自然排序的TreeMap
            for (Map.Entry<Integer, String> entry : sorted.entrySet()) {
        
                System.out.println("Key = " + entry.getKey() +
                        ", Value = " + entry.getValue());
            }
        }
    }

Key = 1, Value = e
    Key = 2, Value = d
    Key = 3, Value = a
    Key = 4, Value = c

# 2. 使用 TreeMap（构造函数） #

public class Test2 {
        
        public static void main(String[] args) throws Exception {
        
            int [] nums={
        3,4,2,1};
            String[]h= {
        "a","c","d","e"};
    
            Map<Integer,String> map = new HashMap<Integer,String>();
            for(int i=0;i<nums.length;i++){
        
                map.put(nums[i],h[i]);
            }
    
            TreeMap<Integer, String> sorted = new TreeMap<>(map);//添加map
    
    //        //TreeMap 存储 HashMap 的值
    //        sorted.putAll(map);
    
            // 显示自然排序的TreeMap
            for (Map.Entry<Integer, String> entry : sorted.entrySet()) {
        
                System.out.println("Key = " + entry.getKey() +
                        ", Value = " + entry.getValue());
            }
        }
    }

Key = 1, Value = e
    Key = 2, Value = d
    Key = 3, Value = a
    Key = 4, Value = c

# 3.使用数组列表 #

public class Test2 {
        
        public static void main(String[] args) throws Exception {
        
            int [] nums={
        3,4,2,1};
            String[]h= {
        "a","c","d","e"};
    
            Map<Integer,String> map = new HashMap<Integer,String>();
            for(int i=0;i<nums.length;i++){
        
                map.put(nums[i],h[i]);
            }
    
            ArrayList<Integer> sortedKeys = new ArrayList<Integer>(map.keySet());
    
            Collections.sort(sortedKeys);
            // Display the TreeMap which is naturally sorted
            for (Integer x : sortedKeys)
                System.out.println("Key = " + x
                        + ", Value = " + map.get(x));
    
        }
    }

Key = 1, Value = e
    Key = 2, Value = d
    Key = 3, Value = a
    Key = 4, Value = c