001/* ObjID.java -- Unique object id with respect to the given host.
002   Copyright (c) 1996, 1997, 1998, 1999, 2004, 2006
003   Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011 
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.rmi.server;
041
042import java.io.DataInput;
043import java.io.DataOutput;
044import java.io.IOException;
045import java.io.ObjectInput;
046import java.io.ObjectOutput;
047import java.io.Serializable;
048
049/**
050 * Represents the object identifier, unique for the host that generated it.
051 * The ObjID contains inside the integer object identifier that, if needed,
052 * may indicated that this is a reference to one of the well known objects
053 * on that host (registry, activator or dgc) and the {@link UID} that 
054 * ensures uniqueness.
055 */
056public final class ObjID
057    implements Serializable
058{
059
060  /**
061   * Use serial version uid for interoperability.
062   */
063  static final long serialVersionUID = - 6386392263968365220L;
064
065  /**
066   * The object counter, which value is assigned when creating the ordinary
067   * objects without the known object id. The counter is incremented each time
068   * the new ObjID is constructed.
069   */
070  private static long next = 0x8000000000000000L;
071
072  /**
073   * The object to put the lock on when incrementing {@link #next}
074   */
075  private static final Object lock = ObjID.class;
076
077  /**
078   * Defines the ID of the naming service.
079   */
080  public static final int REGISTRY_ID = 0;
081
082  /**
083   * Defines the ID of the activator.
084   */
085  public static final int ACTIVATOR_ID = 1;
086
087  /**
088   * Defines the ID of the distributed garbage collector.
089   */
090  public static final int DGC_ID = 2;
091
092  /**
093   * The object Id (either well-known value or the value of the incrementing
094   * object counter.
095   */
096  long objNum;
097
098  /**
099   * The object unique identifier, generated individually for each object.
100   */
101  UID space;
102
103  /**
104   * Create the new object id, unique for this host.
105   */
106  public ObjID()
107  {
108    synchronized (lock)
109      {
110        objNum = next++;
111      }
112    space = new UID();
113  }
114
115  /**
116   * Create the new object id defining the well known remotely accessible
117   * object, present in this host. The well - known objects are:
118   * <ul>
119   * <li>{@link #REGISTRY_ID} - RMI naming service.</li>
120   * <li>{@link #ACTIVATOR_ID} - activator</li>
121   * <li>{@link #DGC_ID} - distributed garbage collector (grants lease
122   * durations to keep the object before it is garbage collected.</li>
123   * </ul>
124   * 
125   * @param id the well known object id, one of the above.
126   */
127  public ObjID(int id)
128  {
129    objNum = (long) id;
130    space = new UID((short) 0);
131  }
132
133  /**
134   * Write object id as long, then the object {@link UID}.
135   */
136  public void write(ObjectOutput out) throws IOException
137  {
138    DataOutput dout = (DataOutput) out;
139    dout.writeLong(objNum);
140    space.write(dout);
141  }
142
143  /**
144   * Read object id (as long), then the object {@link UID}.
145   */
146  public static ObjID read(ObjectInput in) throws IOException
147  {
148    DataInput din = (DataInput) in;
149    ObjID id = new ObjID();
150    id.objNum = din.readLong();
151    id.space = UID.read(din);
152    return (id);
153  }
154
155  /**
156   * Get the hashcode.
157   */
158  public int hashCode()
159  {
160    return space == null ? (int) objNum : space.hashCode() ^ (int) objNum;
161  }
162
163  /**
164   * Compare for equality.
165   */
166  public boolean equals(Object obj)
167  {
168    if (obj instanceof ObjID)
169      {
170        ObjID that = (ObjID) obj;
171        return that.objNum == objNum && eq(that.space, space);
172      }
173    else
174      return false;
175  }
176
177  /**
178   * Compare by .equals if both a and b are not null, compare directly if at
179   * least one of them is null.
180   */
181  static final boolean eq(Object a, Object b)
182  {
183    if (a == null || b == null)
184      return a == b;
185    else
186      return a.equals(b);
187  }  
188  
189  /**
190   * Get the string representation.
191   */
192  public String toString()
193  {
194    return (objNum + ":" + space);
195  }
196
197}