import org.jpox.identity;

public interface OID
{
    /**
     * Provides the OID in a form that can be used by the database as a key.
     * @return The key value
     */
    public abstract Object getKeyValue();

    /**
     * Accessor for the PC class name 
     * @return the PC Class
     */
    public abstract String getPcClass();

    /**
     * Equality operator.
     * @param obj Object to compare against
     * @return Whether they are equal
     */
    public abstract boolean equals(Object obj);

    /**
     * Accessor for the hashcode
     * @return Hashcode for this object
     */
    public abstract int hashCode();

    /**
     * Returns the string representation of the OID.
     * The string representation should contain enough information to be usable as input to a String constructor
     * to create the OID.
     * @return the string representation of the OID.
     */
    public abstract String toString();
}

package org.jpox.identity;

public class OIDImpl implements java.io.Serializable, OID
{
    /** Localiser for messages. */
    protected static final transient Localiser LOCALISER = Localiser.getInstance("org.jpox.store.Localisation");

    /** Separator to use between fields. */
    private transient static final String oidSeparator = "[OID]";

    // JDO spec 5.4.3 - serializable fields required to be public.

    /** The key value. */
    public final Object oid;

    /** The PersistenceCapable class name */
    public final String pcClass;

    /** pre-created toString to improve performance **/ 
    public final String toString;

    /** pre-created hasCode to improve performance **/ 
    public final int hashCode;

    /**
    * Creates an OID with no value. Required by the JDO spec
    */
    public OIDImpl()
    {
        oid = null;
        pcClass = null; 
        toString = null;
        hashCode = -1;
    }

    /**
     * Create a string datastore identity.
     * @param pcClass The PersistenceCapable class that this represents
     * @param object The value
     */
    public OIDImpl(String pcClass, Object object)
    {
        this.pcClass = pcClass;
        this.oid = object;

        StringBuffer s = new StringBuffer();
        s.append(this.oid.toString());
        s.append(oidSeparator);
        s.append(this.pcClass);
        toString = s.toString();
        hashCode = toString.hashCode();        
    }

    /**
     * Constructs an OID from its string representation that is consistent with the output of toString().
     * @param str the string representation of an OID
     * @exception IllegalArgumentException if the given string representation is not valid.
     * @see #toString
     */
    public OIDImpl(String str)
    throws IllegalArgumentException
    {
        if (str.length() < 2)
        {
            throw new IllegalArgumentException(LOCALISER.msg("OID.InvalidValue",str));
        }

        int start = 0;
        int end = str.indexOf(oidSeparator, start);
        String oidStr = str.substring(start, end);
        Object oidValue = null;
        try
        {
            // Use Long if possible, else String
            oidValue = new Long(oidStr);
        }
        catch (NumberFormatException nfe)
        {
            oidValue = oidStr;
        }
        oid = oidValue;

        start = end + oidSeparator.length();
        this.pcClass = str.substring(start, str.length());
        
        toString = str;
        hashCode = toString.hashCode();
    }

    /**
     * Accessor for the key value.
     * @return The key value
     */
    public Object getKeyValue()
    {
        return oid;
    }

    /**
     * Accessor for the PersistenceCapable class name.
     * @return PC class name
     */
    public String getPcClass()
    {
        return pcClass;
    }

    /**
     * Equality operator.
     * @param obj Object to compare against
     * @return Whether they are equal
     */
    public boolean equals(Object obj)
    {
        if (obj == null)
        {
            return false;
        }
        if (obj == this)
        {
            return true;
        }
        if (!(obj.getClass().getName().equals(ClassNameConstants.OIDImpl)))
        {
            return false;
        }
        if (hashCode() != obj.hashCode())
        {
            return false;
        }
        return true;
    }

    /**
     * Accessor for the hashcode
     * @return Hashcode for this object
     */
    public int hashCode()
    {
        return hashCode;
    }

    /**
     * Creates a String representation of the datastore identity, formed from the PC class name
     * and the key value. This will be something like
     * <pre>3254[OID]mydomain.MyClass</pre>
     * @return The String form of the identity
     */
    public String toString()
    {
        return toString;
    }
}

<?xml version="1.0"?>
<plugin id="mydomain" name="JPOX plug-ins" provider-name="My Company">
    <extension point="org.jpox.store_datastoreidentity">
        <datastoreidentity name="myoid" class-name="mydomain.MyOIDImpl" unique="true"/>
    </extension>
</plugin>