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DataNucleus Core provides the primary components of a heterogenous Java persistence solution. It supports persistence API's being layered on top of the core functionality.

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/**********************************************************************
Copyright (c) 2007 Xuan Baldauf and others. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Contributors:
2007 Andy Jefferson - generalised for all datastores
    ...
**********************************************************************/
package org.datanucleus.identity;

/**
 * Identity for use with datastore-identity where the datastore provides a unique "identity" long key per object
 * and hence doesn't need the class name. The behaviour of this class is governed by JDO spec 5.4.3.
 */
public class DatastoreUniqueLongId implements java.io.Serializable, DatastoreId, Comparable
{
    // JDO spec 5.4.3 says: all serializable fields of ObjectID classes are required to be public.

    private static final long serialVersionUID = -8633190725867210874L;
    public final long key;

    public DatastoreUniqueLongId()
    {
        this.key = -1;
    }

    public DatastoreUniqueLongId(long key)
    {
        this.key = key;
    }

    /**
     * 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 DatastoreUniqueLongId(String str)
    throws IllegalArgumentException
    {
        this.key = Long.parseLong(str);
    }

    public Object getKeyAsObject()
    {
        return Long.valueOf(key);
    }

    public long getKey()
    {
        return key;
    }

    public String getTargetClassName()
    {
        // We do not need a class name.
        throw new UnsupportedOperationException();
    }

    public boolean equals(Object obj)
    {
        if (obj == this)
        {
            return true;
        }
        if (obj == null)
        {
            return false;
        }
        if (!(obj.getClass().equals(this.getClass())))
        {
            return false;
        }
        return key == ((DatastoreUniqueLongId)obj).key;
    }

    public int compareTo(Object o)
    {
        if (o instanceof DatastoreUniqueLongId)
        {
            DatastoreUniqueLongId c = (DatastoreUniqueLongId)o;
            return (int)(this.key - c.key);
        }
        else if (o == null)
        {
            throw new ClassCastException("object is null");
        }
        throw new ClassCastException(this.getClass().getName() + " != " + o.getClass().getName());
    }

    public int hashCode()
    {
        // Assume that we wont overflow the int range
        return (int) key; 
    }

    /**
     * Creates a String representation of the datastore identity, formed from the key value. 
     * This will be something like 3254
     * @return The String form of the identity
     */
    public String toString()
    {
        return Long.toString(key);
    }
}