sourcemedia.java

Hiberante程序高手秘籍的源代码

package com.oreilly.hh;

import java.util.*;
import java.io.Serializable;

/**
 * This is a typesafe enumeration that identifies the media on which an
 * item in our music database was obtained.
 **/
public class SourceMedia implements Serializable {

    /**
     * Stores the external name of this instance, by which it can be retrieved.
     */
    private final String name;

    /**
     * Stores the human-readable description of this instance, by which it is
     * identified in the user interface.
     */
    private final transient String description;

    /**
     * Return the external name associated with this instance. <p>
     * 
     * @return the name by which this instance is identified in code.
     **/
    public String getName() {
        return name;
    }

    /**
     * Return the description associated with this instance. <p>
     * 
     * @return the human-readable description by which this instance is
     *         identified in the user interface.
     **/
    public String getDescription() {
        return description;
    }

    /**
     * Keeps track of all instances by name, for efficient lookup.
     */
    private static final Map instancesByName = new HashMap();

    /**
     * Constructor is private to prevent instantiation except during class
     * loading.
     * 
     * @param name the external name of the message type.
     * @param description the human readable description of the message type,
     *        by which it is presented in the user interface.
     */
    private SourceMedia(String name, String description) {
        this.name = name;
        this.description = description;

        // Record this instance in the collection that tracks the enumeration
        instancesByName.put(name, this);
    }

    /**
     * The instance that represents music obtained from cassette tape.
     */
    public static final SourceMedia CASSETTE =
        new SourceMedia("cassette", "Audio Cassette Tape");

    /**
     * The instance that represents music obtained from vinyl.
     */
    public static final SourceMedia VINYL =
        new SourceMedia("vinyl", "Vinyl Record");

    /**
     * The instance that represents music obtained from VHS tapes.
     */
    public static final SourceMedia VHS =
        new SourceMedia("vhs", "VHS Videocassette Tape");

    /**
     * The instance that represents music obtained from a compact disc.
     */
    public static final SourceMedia CD =
        new SourceMedia("cd", "Compact Disc");

    /**
     * The instance that represents music obtained from a broadcast.
     */
    public static final SourceMedia BROADCAST =
        new SourceMedia("broadcast", "Analog Broadcast");

    /**
     * The instance that represents music obtained as an Internet download.
     */
    public static final SourceMedia DOWNLOAD =
        new SourceMedia("download", "Internet Download");

    /**
     * The instance that represents music from a digital audio stream.
     */
    public static final SourceMedia STREAM =
        new SourceMedia("stream", "Digital Audio Stream");

    /**
     * Obtain the collection of all legal enumeration values.
     *
     * @return all instances of this typesafe enumeration.
     */
    public static Collection getAllValues() {
        return Collections.unmodifiableCollection(instancesByName.values());
    }

    /**
     * Look up an instance by name.
     *
     * @param name the external name of an instance.
     * @return the corresponding instance.
     * @throws NoSuchElementException if there is no such instance.
     */
    public static SourceMedia getInstanceByName(String name) {
        SourceMedia result = (SourceMedia)instancesByName.get(name);
        if (result == null) {
            throw new NoSuchElementException(name);
        }
        return result;
    }

    /**
     * Return a string representation of this object.
     */
        public String toString() {
        return description;
    }

    /**
     * Insure that deserialization preserves the signleton property.
     */
    private Object readResolve() {
        return getInstanceByName(name);
    }
}