向Java枚举类型中加入新方法

Posted 2020-09-20 clnchanpin

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


以下是一个样例：返回对实例自身的描写叙述，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：能够调用对应枚举成员的方法来生成对应的对象，比方以下的OFType，能够这样使用：

OFType t = OFType.HELLO;

t.newInstance();

以下是Floodlight controller中相关知识点的体现

public enum OFType {
    //这里自己定义构造方法。有三个參数
    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;

    //每一个消息类型，都须要相应的详细实现类
    protected Class<? extends OFMessage> clazz;

    //每一个消息类的无參构造器
    protected Constructor<? extends OFMessage> constructor;

    //接口 Instantiable 有一个初始化实例的方法。创建详细的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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