java - 当我们只给出 1 个参数值时，如何获取某个枚举实例？

Question

请在下面找到我的枚举类:

public enum CountryCode //implements IEnum
{
AD("Andorra", "AND", "Europe", "South West Europe"),
AE("United Arab Emirates", "ARE", "Asia", "South West Asia"),
AF("Afghanistan", "AFG", "Asia", "South Asia"),
// and so one till Z

// attributes defined
private final String label;
private final String isoCode3;
private final String continent;
private final String region;

// countructor defined
private CountryCode(String label, String isoCode3, String continent, String region)
{
    this.label = label;
    this.isoCode3 = isoCode3;
    this.continent = continent;
    this.region = region;

}   // END CountryCode

} // END enum CountryCode

现在，如果我只得到国家/地区名称(即标签)，那么我将如何获取其相应的枚举实例？因此，如果给定“Andorra”，我想要 AD。

Answer 1

我会缓存 Map 中的关系，其中键是标签，值是相应的 CountryCode 实例。这样，您只需迭代一次 CountryCode 实例，而不是每次调用 getByLabel() 方法时。

public enum CountryCode {

    AD("Andorra", "AND", "Europe", "South West Europe"),
    AE("United Arab Emirates", "ARE", "Asia", "South West Asia"),
    AF("Afghanistan", "AFG", "Asia", "South Asia");

    private static final Map<String, CountryCode> BY_LABEL;
    static {
        Map<String, CountryCode> byLabel = new HashMap<String, CountryCode>();
        for (CountryCode countryCode : values()) {
            byLabel.put(countryCode.label, countryCode);
        }
        BY_LABEL = Collections.unmodifiableMap(byLabel);
    }

    private final String label;
    private final String isoCode3;
    private final String continent;
    private final String region;

    private CountryCode(String label, String isoCode3, String continent, String region) {
        this.label = label;
        this.isoCode3 = isoCode3;
        this.continent = continent;
        this.region = region;
    }

    public static CountryCode getByLabel(String label) {
        return BY_LABEL.get(label);
    }

}

然后，只需调用:

CountryCode countryCode = CountryCode.getByLabel("Andorra");