No enum constant XXX.name，Enum$valueOf()，入参类型为枚举对象名

目录

使用场景

原因

valueOf源码

enumConstantDirectory源码

---

使用valueOf()出现异常

使用场景

public enum CertificateType {

    ID_CARD(1, "身份证"),
    PASSPORT(2, "护照"),
    OTHERS(3, "其他"),
    ORGANIZATION(4, "组织机构代码"),
    BUSINESS_LICENSE(5, "营业证号"),
    ;
}

//发生错误的代码
CertificateType type = CertificateType.valueOf("身份证");

原因

valueOf方法的入参类型为枚举对象名

valueOf源码

public abstract class Enum>
        implements Comparable, Serializable {

    public static > T valueOf(Class enumType,
                                                String name) {
        T result = enumType.enumConstantDirectory().get(name);
        if (result != null)
            return result;
        if (name == null)
            throw new NullPointerException("Name is null");
        throw new IllegalArgumentException(
            "No enum constant " + enumType.getCanonicalName() + "." + name);
    }
}

valueOf核心为enumConstantDirectory()，获取结果见下图

valueOf获取的结果为​​​​​​

enumConstantDirectory源码

public final class Class implements java.io.Serializable,
                              GenericDeclaration,
                              Type,
                              AnnotatedElement {
   
    Map enumConstantDirectory() {
        if (enumConstantDirectory == null) {
            T[] universe = getEnumConstantsShared();
            if (universe == null)
                throw new IllegalArgumentException(
                    getName() + " is not an enum type");
            Map m = new HashMap<>(2 * universe.length);
            for (T constant : universe)
                m.put(((Enum)constant).name(), constant);
            enumConstantDirectory = m;
        }
        return enumConstantDirectory;
    }
    private volatile transient Map enumConstantDirectory = null;
}

拿到当前枚举类的各个对象组装结果如下：