[Java] HashMap 정렬하기

List 오름차순 (Key 정렬)

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void solution1(String[] sNation, String[] sCapital) {
        Map<String , String> map = new HashMap<>();

        for (int i = 0; i < sNation.length; i++) {
            map.put(sNation[i], map.getOrDefault(sNation[i], sCapital[i]));
        }

        List<String> keyList = new ArrayList<>(map.keySet());
        keyList.sort((s1,s2) -> s1.compareTo(s2));

        for (String key : keyList) {
            System.out.println("Key : " + key + ", Value : " + map.get(key));
        }
    }

    public static void main(String[] args) {

        String[] sNation = {"KOREA","JAPAN","CHINA","USA"};
        String[] sCapital = {"SEOUL", "TOKYO", "BEIJING", "WASHINGTON"};

        System.out.println("==== List 오름차순 (Key 정렬) ====");
        solution1(sNation, sCapital);
        
        
//        ==== List 오름차순 (Key 정렬) ====
//        Key : CHINA, Value : BEIJING
//        Key : JAPAN, Value : TOKYO
//        Key : KOREA, Value : SEOUL
//        Key : USA,   Value : WASHINGTON
    }
}

List 오름차순 (Value 정렬)

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void solution2(String[] sNation, String[] sCapital) {
        Map<String , String> map = new HashMap<>();

        for (int i = 0; i < sNation.length; i++) {
            map.put(sNation[i], map.getOrDefault(sNation[i], sCapital[i]));
        }

        List<String> valueList = new ArrayList<>(map.values());
        valueList.sort(String::compareTo);

        for (String value : valueList) {
            System.out.println("Value : " + value);
        }

    }

    public static void main(String[] args) {

        String[] sNation = {"KOREA","JAPAN","CHINA","USA"};
        String[] sCapital = {"SEOUL", "TOKYO", "BEIJING", "WASHINGTON"};

        System.out.println("==== List 오름차순 (value 정렬) ====");
        solution2(sNation, sCapital);
        
//        ==== List 오름차순 (value 정렬) ====
//        Value : BEIJING
//        Value : SEOUL
//        Value : TOKYO
//        Value : WASHINGTON
    }
}

Stream 오름차순 (Key 정렬)

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void solution3(String[] sNation, String[] sCapital) {
        Map<String , String> map = new HashMap<>();

        for (int i = 0; i < sNation.length; i++) {
            map.put(sNation[i], map.getOrDefault(sNation[i], sCapital[i]));
        }

        List<Map.Entry<String, String>> entries = map.entrySet().stream()
                .sorted(Map.Entry.comparingByKey())
                .collect(Collectors.toList());
                
        for (Map.Entry<String,String> entry : entries) {
            System.out.println("Key : " + entry.getKey() + ", Value : " + entry.getValue());
        }

    }

    public static void main(String[] args) {

        String[] sNation = {"KOREA","JAPAN","CHINA","USA"};
        String[] sCapital = {"SEOUL", "TOKYO", "BEIJING", "WASHINGTON"};

        System.out.println("==== Stream 오름차순 (Key 정렬) ====");
        solution3(sNation, sCapital);
        
//        ==== Stream 오름차순 (Key 정렬) ====
//        Key : CHINA, Value : BEIJING
//        Key : JAPAN, Value : TOKYO
//        Key : KOREA, Value : SEOUL
//        Key : USA,   Value : WASHINGTON
    }
}

Stream 오름차순 (Value 정렬)

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void solution4(String[] sNation, String[] sCapital) {
        Map<String , String> map = new HashMap<>();

        for (int i = 0; i < sNation.length; i++) {
            map.put(sNation[i], map.getOrDefault(sNation[i], sCapital[i]));
        }

        // Map.Entry 리스트 생성
        List<Map.Entry<String, String>> entries = new ArrayList<>(map.entrySet());

        // 리스트를 value 기준으로 정렬
        
        // 방법 1
        entries.sort((entry1, entry2) -> 
        	entry1.getValue().compareTo(entry2.getValue()));  
        // 방법 2
        entries.sort(Comparator.comparing(Entry::getValue));	
        // 방법 3
        entries.sort(Entry.comparingByValue());              
        
        for (Map.Entry<String, String> entry : entries) {
            System.out.println("Key : " + entry.getKey() + ", Value : " + entry.getValue());
        }

    }

    public static void main(String[] args) {

        String[] sNation = {"KOREA","JAPAN","CHINA","USA"};
        String[] sCapital = {"SEOUL", "TOKYO", "BEIJING", "WASHINGTON"};

        System.out.println("==== Stream 오름차순 (Value 정렬) ====");
        solution4(sNation, sCapital);
        
//        ==== Stream 오름차순 (Value 정렬) ====
//        Key : CHINA, Value : BEIJING
//        Key : KOREA, Value : SEOUL
//        Key : JAPAN, Value : TOKYO
//        Key : USA,   Value : WASHINGTON       
    }
}