為什么枚舉的構(gòu)造函數(shù)不能訪問靜態(tài)字段和方法？這對(duì)于一個(gè)類是完全有效的，但對(duì)于枚舉是不允許的。我正在嘗試將枚舉實(shí)例存儲(chǔ)在靜態(tài)Map中?？紤]下面的示例代碼，它允許通過abbreivation查找：public enum Day {    Sunday("Sun"), Monday("Mon"), Tuesday("Tue"), Wednesday("Wed"), Thursday("Thu"), Friday("Fri"), Saturday("Sat");    private final String abbreviation;    private static final Map<String, Day> ABBREV_MAP = new HashMap<String, Day>();    private Day(String abbreviation) {        this.abbreviation = abbreviation;        ABBREV_MAP.put(abbreviation, this);  // Not valid    }    public String getAbbreviation() {        return abbreviation;    }    public static Day getByAbbreviation(String abbreviation) {        return ABBREV_MAP.get(abbreviation);    }}這將不起作用，因?yàn)槊杜e不允許在其構(gòu)造函數(shù)中使用靜態(tài)引用。但是，它只是在實(shí)現(xiàn)為類的情況下才起作用：public static final Day SUNDAY = new Day("Sunday", "Sun");private Day(String name, String abbreviation) {    this.name = name;    this.abbreviation = abbreviation;    ABBREV_MAP.put(abbreviation, this);  // Valid}