java - 具有数字常量的枚举类型

Question

我从遗留系统获取数据，其中某个字节字段是可能包含字母或数字的代码。我想将它映射到一个枚举，但我不确定如何处理数值。

public enum UsageCode {
    A ("Antique"),
    F ("Flood Damaged"),
    N ("New");
//  0 ("Unknown")  How to allow for value of "0"?

    private final String description;

    UsageCode(String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }
}

Answer 1

把它翻过来:

public enum UsageCode {
    ANTIQUE ('A'),
    FLOOD_DAMAGED ('F'),
    NEW ('N');
    UNKNOWN ('0')

    private static final Map<Character, UsageCode> charToEnum
            = new HashMap<Character, UsageCode>();

    static { // Initialize map from legacy code to enum constant
        for (UsageCode code : values())
        charToEnum.put(code.getCode(), code);
    }

    // Returns UsageCode for legacy character code, or null if code is invalid
    public static UsageCode fromLegacyCode(char code) {
        return charToEnum.get(code);
    }

    private final char code;

    UsageCode(char code) {
        this.code = code;
    }

    public char getCode() {
        return code;
    }
}

为了将传入的字符代码转换为枚举值，我添加了一个内部 Map<Character, UsageCode>和静态转换方法。

示例改编自 Effective Java 2nd Edition , 第 30 条。