Java创建不可修改的静态常量集合

如下代码
举例了：List、Map、Set的创建方式

源码

import java.util.*;

public class ConstantUtil {
    public static final List LIST;
    public static final Map MAP;
    public static final Set SET;

    static {
        ArrayList list = new ArrayList<>();
        list.add("v1");
        list.add("v2");
        LIST = Collections.unmodifiableList(list);
        HashMap map = new HashMap<>();
        map.put("k1", "v1");
        map.put("k2", "v2");
        MAP = Collections.unmodifiableMap(map);
        HashSet set = new HashSet<>();
        set.add("v1");
        set.add("v2");
        SET = Collections.unmodifiableSet(set);
    }
}