java - 我应该选择哪种方法 fromValue() 函数枚举

Question

嗨，我想在 ENUM 中提供 fromValue() 函数。您能否提供您宝贵的建议，我应该选择哪种方法:-

1. 这里我们每次迭代 ENUM 值并返回匹配的结果。

<p></p>

<pre><code>    public enum DAY {
        SUNDAY("sunday"),
        MONDAY("monday"),
        TUESDAY("tuesday"),
        UNKNOWN("unknown");

        private final String value;

        DAY(final String value) {
            this.value = value;
        }

        public String value() {
            return value;
        }

        public static DAY fromValue(final String value) {
            return Stream.of(DAY.values())
                    .filter( day -> day.value().equals(value))
                    .findAny()
                    .orElse(UNKNOWN);
        }
    }
</code></pre>

<p></p>

在这种方法中，我们使用静态 block 创建键值映射并返回值而无需迭代。但这里我们需要使用“静态 block ”

    public enum DAY {<p></p>

<pre><code>    SUNDAY("sunday"),
    MONDAY("monday"),
    TUESDAY("tuesday"),
    UNKNOWN("unknown");

    private final String value;

    DAY(final String value) {
        this.value = value;
    }

    private static final Map<String, DAY> VALUE_TO_TYPE = new HashMap<>();

    static {
        Stream.of(DAY.values()).forEach(type -> VALUE_TO_TYPE.put(type.value, type));
    }

    public String value() {
        return value;
    }

    public static DAY fromValue(final String value) {
        final DAY day = VALUE_TO_TYPE.get(value);
        return day != null ?  day : UNKNOWN;
    }
}
</code></pre>

<p></p>

Answer 1

采用第二种方法，稍加修改。

public enum DAY {<p></p>

<pre><code>    SUNDAY("sunday"),
    MONDAY("monday"),
    TUESDAY("tuesday"),
    UNKNOWN("unknown");

    private final String value;

    DAY(final String value) {
        this.value = value;
    }

    private static final Map<String, DAY> VALUE_TO_TYPE = Stream.of(DAY.values()).collect(Collectors.toMap(d -> d.value, d -> d));

    public String value() {
        return value;
    }

   public static Optional<DAY> fromValue(final String value) {
       return Optional.ofNullable(VALUE_TO_TYPE.get(value));
   }
}
</code></pre>

<p></p>