Enum Class

枚举是个好东西

一、简单的枚举使用

每一个enum都会继承Enum类
原始的Enum只具有两个属性ordinal、name
每一个枚举数据都是枚举对象
枚举可以方便的使用在switch中

public enum Light {
    RED , GREEN , YELLOW ;
}

public class App {
    public static void main(String[] args) {
        System.out.println(Light.GREEN);
        System.out.println(Light.GREEN.ordinal());
        System.out.println(Light.GREEN.name());
    }
}

输出
------
GREEN
1
GREEN

二、枚举基本使用

每一个枚举类都可以新加一些属性，然后通过override toString的方法来实现name的映射

public enum Light2 {

    // 利用构造函数传参
    RED ("red"), 
    GREEN ("green"), 
    YELLOW ("yellow");

    // 定义私有变量
    private String nCode

    // 构造函数，枚举类型只能为私有
    private Light2(String _nCode) {
        this.nCode1 = _nCode;
    }

    @Override
    public String toString() {
        return String.valueOf(this.nCode1);
    }
}


public class App {
    public static void main(String[] args) {
        System.out.println(Light2.GREEN);
        System.out.println(Light2.GREEN.ordinal());
        System.out.println(Light2.GREEN.name());
    }
}

输出
---
green
1
GREEN

三、枚举映射

将映射关系存入map中

import java.util.HashMap;
import java.util.Map;

public class Network {

    public static class NetworkValue {

        public static final NetworkValue UNKNOWN = new NetworkValue(-1);

        public static final NetworkValue WIFI = new NetworkValue(1);

        public static final NetworkValue NETWORK_2G = new NetworkValue(2);

        public static final NetworkValue NETWORK_3G = new NetworkValue(3);

        public static final NetworkValue NETWORK_4G = new NetworkValue(4);

        public static final NetworkValue NETWORK_5G = new NetworkValue(5);

        public static final NetworkValue OTHER_MOBILE_NETWORK = new NetworkValue(6);

        private int value = -1;

        private NetworkValue(int value) {
            this.value = value;
        }

        public int getValue() {
            return value;
        }

        @Override
        public String toString() {
            return String.valueOf(value);
        }

        @Override
        public boolean equals(Object obj) {
            boolean ret = false;

            if (obj instanceof NetworkValue) {
                ret = (value == ((NetworkValue)obj).value);
            } else if (obj instanceof Integer) {
                ret = (value == (Integer)obj);
            }

            return ret;
        }
    }

    public static class NetworkValueDesc {

        public static final NetworkValueDesc UNKNOWN = new NetworkValueDesc("unknown");

        public static final NetworkValueDesc WIFI = new NetworkValueDesc("wifi");

        public static final NetworkValueDesc NETWORK_2G = new NetworkValueDesc("2g");

        public static final NetworkValueDesc NETWORK_3G = new NetworkValueDesc("3g");

        public static final NetworkValueDesc NETWORK_4G = new NetworkValueDesc("4g");

        public static final NetworkValueDesc NETWORK_5G = new NetworkValueDesc("5g");

        public static final NetworkValueDesc OTHER_MOBILE_NETWORK = new NetworkValueDesc("other");

        private String value = null;

        private NetworkValueDesc(String value) {
            this.value = value;
        }

        @Override
        public String toString() {
            return value;
        }
    }

    public static Map<Integer, String> network_value_desc = new HashMap<Integer, String>();

    static {
        network_value_desc.put(NetworkValue.UNKNOWN.getValue(), NetworkValueDesc.UNKNOWN.toString());
        network_value_desc.put(NetworkValue.WIFI.getValue(), NetworkValueDesc.WIFI.toString());
        network_value_desc.put(NetworkValue.NETWORK_2G.getValue(), NetworkValueDesc.NETWORK_2G.toString());
        network_value_desc.put(NetworkValue.NETWORK_3G.getValue(), NetworkValueDesc.NETWORK_3G.toString());
        network_value_desc.put(NetworkValue.NETWORK_4G.getValue(), NetworkValueDesc.NETWORK_4G.toString());
        network_value_desc.put(NetworkValue.NETWORK_5G.getValue(), NetworkValueDesc.NETWORK_5G.toString());
        network_value_desc.put(NetworkValue.OTHER_MOBILE_NETWORK.getValue(), NetworkValueDesc.OTHER_MOBILE_NETWORK.toString());
    }

    public static String getNetwork(String network_str) {
        int network = NetworkValue.UNKNOWN.getValue();
        try {
            network = Integer.valueOf(network_str);
        } catch (Exception e){
        }
        return getNetwork(network);
    }

    public static String getNetwork(int network) {
        String ret = network_value_desc.get(network);
        if (ret == null) {
            ret = NetworkValueDesc.UNKNOWN.toString();
        }
        return ret;
    }

}

abstract class Enum

package java.lang;

import java.io.Serializable;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;

/**
 * This is the common base class of all Java language enumeration types.
 *
 * More information about enums, including descriptions of the
 * implicitly declared methods synthesized by the compiler, can be
 * found in section 8.9 of
 * <cite>The Java&trade; Language Specification</cite>.
 *
 * <p> Note that when using an enumeration type as the type of a set
 * or as the type of the keys in a map, specialized and efficient
 * {@linkplain java.util.EnumSet set} and {@linkplain
 * java.util.EnumMap map} implementations are available.
 *
 * @param <E> The enum type subclass
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see     Class#getEnumConstants()
 * @see     java.util.EnumSet
 * @see     java.util.EnumMap
 * @since   1.5
 */
public abstract class Enum<E extends Enum<E>>
        implements Comparable<E>, Serializable {
    /**
     * The name of this enum constant, as declared in the enum declaration.
     * Most programmers should use the {@link #toString} method rather than
     * accessing this field.
     */
    private final String name;

    /**
     * Returns the name of this enum constant, exactly as declared in its
     * enum declaration.
     *
     * <b>Most programmers should use the {@link #toString} method in
     * preference to this one, as the toString method may return
     * a more user-friendly name.</b>  This method is designed primarily for
     * use in specialized situations where correctness depends on getting the
     * exact name, which will not vary from release to release.
     *
     * @return the name of this enum constant
     */
    public final String name() {
        return name;
    }

    /**
     * The ordinal of this enumeration constant (its position
     * in the enum declaration, where the initial constant is assigned
     * an ordinal of zero).
     *
     * Most programmers will have no use for this field.  It is designed
     * for use by sophisticated enum-based data structures, such as
     * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
     */
    private final int ordinal;

    /**
     * Returns the ordinal of this enumeration constant (its position
     * in its enum declaration, where the initial constant is assigned
     * an ordinal of zero).
     *
     * Most programmers will have no use for this method.  It is
     * designed for use by sophisticated enum-based data structures, such
     * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
     *
     * @return the ordinal of this enumeration constant
     */
    public final int ordinal() {
        return ordinal;
    }

    /**
     * Sole constructor.  Programmers cannot invoke this constructor.
     * It is for use by code emitted by the compiler in response to
     * enum type declarations.
     *
     * @param name - The name of this enum constant, which is the identifier
     *               used to declare it.
     * @param ordinal - The ordinal of this enumeration constant (its position
     *         in the enum declaration, where the initial constant is assigned
     *         an ordinal of zero).
     */
    protected Enum(String name, int ordinal) {
        this.name = name;
        this.ordinal = ordinal;
    }

    /**
     * Returns the name of this enum constant, as contained in the
     * declaration.  This method may be overridden, though it typically
     * is not necessary or desirable.  An enum type should override this
     * method when a more "programmer-friendly" string form exists.
     *
     * @return the name of this enum constant
     */
    public String toString() {
        return name;
    }

    /**
     * Returns true if the specified object is equal to this
     * enum constant.
     *
     * @param other the object to be compared for equality with this object.
     * @return  true if the specified object is equal to this
     *          enum constant.
     */
    public final boolean equals(Object other) {
        return this==other;
    }

    /**
     * Returns a hash code for this enum constant.
     *
     * @return a hash code for this enum constant.
     */
    public final int hashCode() {
        return super.hashCode();
    }

    /**
     * Throws CloneNotSupportedException.  This guarantees that enums
     * are never cloned, which is necessary to preserve their "singleton"
     * status.
     *
     * @return (never returns)
     */
    protected final Object clone() throws CloneNotSupportedException {
        throw new CloneNotSupportedException();
    }

    /**
     * Compares this enum with the specified object for order.  Returns a
     * negative integer, zero, or a positive integer as this object is less
     * than, equal to, or greater than the specified object.
     *
     * Enum constants are only comparable to other enum constants of the
     * same enum type.  The natural order implemented by this
     * method is the order in which the constants are declared.
     */
    public final int compareTo(E o) {
        Enum<?> other = (Enum<?>)o;
        Enum<E> self = this;
        if (self.getClass() != other.getClass() && // optimization
            self.getDeclaringClass() != other.getDeclaringClass())
            throw new ClassCastException();
        return self.ordinal - other.ordinal;
    }

    /**
     * Returns the Class object corresponding to this enum constant's
     * enum type.  Two enum constants e1 and  e2 are of the
     * same enum type if and only if
     *   e1.getDeclaringClass() == e2.getDeclaringClass().
     * (The value returned by this method may differ from the one returned
     * by the {@link Object#getClass} method for enum constants with
     * constant-specific class bodies.)
     *
     * @return the Class object corresponding to this enum constant's
     *     enum type
     */
    @SuppressWarnings("unchecked")
    public final Class<E> getDeclaringClass() {
        Class<?> clazz = getClass();
        Class<?> zuper = clazz.getSuperclass();
        return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
    }

    /**
     * Returns the enum constant of the specified enum type with the
     * specified name.  The name must match exactly an identifier used
     * to declare an enum constant in this type.  (Extraneous whitespace
     * characters are not permitted.)
     *
     * <p>Note that for a particular enum type {@code T}, the
     * implicitly declared {@code public static T valueOf(String)}
     * method on that enum may be used instead of this method to map
     * from a name to the corresponding enum constant.  All the
     * constants of an enum type can be obtained by calling the
     * implicit {@code public static T[] values()} method of that
     * type.
     *
     * @param <T> The enum type whose constant is to be returned
     * @param enumType the {@code Class} object of the enum type from which
     *      to return a constant
     * @param name the name of the constant to return
     * @return the enum constant of the specified enum type with the
     *      specified name
     * @throws IllegalArgumentException if the specified enum type has
     *         no constant with the specified name, or the specified
     *         class object does not represent an enum type
     * @throws NullPointerException if {@code enumType} or {@code name}
     *         is null
     * @since 1.5
     */
    public static <T extends Enum<T>> T valueOf(Class<T> 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);
    }

    /**
     * enum classes cannot have finalize methods.
     */
    protected final void finalize() { }

    /**
     * prevent default deserialization
     */
    private void readObject(ObjectInputStream in) throws IOException,
        ClassNotFoundException {
        throw new InvalidObjectException("can't deserialize enum");
    }

    private void readObjectNoData() throws ObjectStreamException {
        throw new InvalidObjectException("can't deserialize enum");
    }
}