如何限制用户使用Java流从列表中选择两个枚举?

Question

我有一个enum类，用户可以从中选择最多2个选项。如果他选择了多于2个，就会显示一个错误信息。

我想用Java流来做这件事。我仍在努力弄清楚它们是如何工作的。

到目前为止，我在 下面写了这段代码:

public enum UserSkills {
HARD_WORKNG("HARD_WORKNG"),
ON_TIME("ON_TIME"),
HONEST("HONEST");
public final String value;
UserSkills(String value) {
this.value = value;
}
@Override
public String toString() {
return name() + "[" + value + "]";
}
public static List < UserSkills > of (String userSkills) {
notNull(userSkills, "userSkills cannot be null");
return Arrays.stream(values())
.flatMap(s - > {
if (values().length > 3) {
throw new IllegalArgumentException(String.format("you can only choose up to 3 user skills", userSkills));
} else {
}
}).collect(Collectors.toList());
}
}

我不知道如何完成它，如有任何建议，不胜感激。

Answer 1

似乎方法of应该接受一个变量String ... userSkills(或者输入字符串应该以某种方式分割以识别多个enum值):

public static List<UserSkills> of (String ... userSkills) {
List<UserSkills> result = Arrays.stream(userSkills)
.filter(Objects::nonNull)
.map(UserSkills::valueOf) // throws IllegalArgumentException no enum constant
.distinct()
.collect(Collectors.toList());

if (result.size() > 2) {
throw new IllegalArgumentException("Only 2 skills can be selected");
}
return result;
}

测试:

List<UserSkills> skills = UserSkills.of(null, "HARD_WORKNG", "HONEST", "HARD_WORKNG", "ON_TIME");
Exception in thread "main" java.lang.IllegalArgumentException: Only 2 skills can be selected

List<UserSkills> skills = UserSkills.of(null, "HARD_WORKNG", "HONEST", "HARD_WORKNG");
System.out.println(skills);

输出:

[HARD_WORKNG[HARD_WORKNG], HONEST[HONEST]]