向Java枚举类型中添加新方法

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除了不能继承enum之外，可将其看做一个常规类。甚至可以有main方法。
注意：必须先定义enum实例，实例的最后有一个分号。

下面是一个例子：返回对实例自身的描述，而非默认的toString返回枚举实例的名字。

public enum Color {RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);    // 成员变量    private String name;    private int index;    // 构造方法    private Color(String name, int index) {        this.name = name;        this.index = index;    }    public static String getName(int index) {    //利用了枚举自身的values()方法；        for (Color c : Color.values()) {            if (c.getIndex() == index) {                return c.name;            }        }        return null;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

重要性在于：可以调用相应枚举成员的方法来生成相应的对象，比如下面的OFType，可以这样使用：

OFType t = OFType.HELLO;

t.newInstance();

下面是Floodlight controller中相关知识点的体现

public enum OFType {    //这里自定义构造方法，有三个参数    HELLO               (0, OFHello.class, new Instantiable<OFMessage>() {                            @Override                            public OFMessage instantiate() {                                return new OFHello();                            }}),    ERROR               (1, OFError.class, new Instantiable<OFMessage>() {                            @Override                            public OFMessage instantiate() {                                return new OFError();                            }}),     PACKET_IN           (10, OFPacketIn.class, new Instantiable<OFMessage>() {                            @Override                            public OFMessage instantiate() {                                return new OFPacketIn();                            }}),    PACKET_OUT          (13, OFPacketOut.class, new Instantiable<OFMessage>() {                            @Override                            public OFMessage instantiate() {                                return new OFPacketOut();                            }}),    FLOW_MOD            (14, OFFlowMod.class, new Instantiable<OFMessage>() {                            @Override                            public OFMessage instantiate() {                                return new OFFlowMod();                            }});    static OFType[] mapping;    //每个消息类型，都需要对应的具体实现类    protected Class<? extends OFMessage> clazz;    //每个消息类的无参构造器    protected Constructor<? extends OFMessage> constructor;    //接口 Instantiable 有一个初始化实例的方法，创建具体的OFMessage    protected Instantiable<OFMessage> instantiable;    //消息类型的值    protected byte type;    /**构造方法     * Store some information about the OpenFlow type, including wire protocol     * type number, length, and derived class     *     * @param type Wire protocol number associated with this OFType     * @param requestClass The Java class corresponding to this type of OpenFlow message     * @param instantiator An Instantiator<OFMessage> implementation that creates an     *          instance of the specified OFMessage     */    OFType(int type, Class<? extends OFMessage> clazz, Instantiable<OFMessage> instantiator) {        this.type = (byte) type;        this.clazz = clazz;        this.instantiable = instantiator;        try {            this.constructor = clazz.getConstructor(new Class[]{});        } catch (Exception e) {            throw new RuntimeException("Failure getting constructor for class: " + clazz, e);        }        OFType.addMapping(this.type, this); //值到枚举类的映射    }    /**     * Adds a mapping from type value to OFType enum     *     * @param i OpenFlow wire protocol type     * @param t type     */    static public void addMapping(byte i, OFType t) {        if (mapping == null)            mapping = new OFType[32];        OFType.mapping[i] = t;    }    /**     * Remove a mapping from type value to OFType enum     *     * @param i OpenFlow wire protocol type     */    static public void removeMapping(byte i) {        OFType.mapping[i] = null;    }    /**     * Given a wire protocol OpenFlow type number, return the OFType associated     * with it     *     * @param i wire protocol number     * @return OFType enum type     */    static public OFType valueOf(Byte i) {        return OFType.mapping[i];    }    /**     * @return Returns the wire protocol value corresponding to this OFType     */    public byte getTypeValue() {        return this.type;    }    /**     * @return return the OFMessage subclass corresponding to this OFType     */    public Class<? extends OFMessage> toClass() {        return clazz;    }    /**     * Returns the no-argument Constructor of the implementation class for     * this OFType     * @return the constructor     */    public Constructor<? extends OFMessage> getConstructor() {        return constructor;    }    /**     * Returns a new instance of the OFMessage represented by this OFType     * @return the new object     */    public OFMessage newInstance() {        return instantiable.instantiate();    }    /**     * @return the instantiable     */    public Instantiable<OFMessage> getInstantiable() {        return instantiable;    }    /**     * @param instantiable the instantiable to set     */    public void setInstantiable(Instantiable<OFMessage> instantiable) {        this.instantiable = instantiable;    }}

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