컬렉션 프레임워크

import java.util.*;

public class CollectionDemo {
    public static void main(String[] args) {
        // List
        List<String> list = new ArrayList<>(Arrays.asList("c","a","b","a"));
        Collections.sort(list);
        System.out.println(list);  // [a, a, b, c]

        // Set (중복 제거)
        Set<String> set = new HashSet<>(list);
        System.out.println(set);   // [a, b, c] (순서 무관)

        // Map
        Map<String, Integer> map = new HashMap<>();
        map.put("java", 90);
        map.put("spring", 85);
        map.put("react", 80);

        // 순회
        for (Map.Entry<String, Integer> entry : map.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }

        // 정렬된 Map
        Map<String, Integer> sorted = new TreeMap<>(map);
        System.out.println(sorted);  // {java=90, react=80, spring=85}
    }
}