libjava/classpath/java/rmi/server/ObjID.java

   1 /* ObjID.java -- Unique object id with respect to the given host.
   2    Copyright (c) 1996, 1997, 1998, 1999, 2004, 2006
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package java.rmi.server;
  41
  42 import java.io.DataInput;
  43 import java.io.DataOutput;
  44 import java.io.IOException;
  45 import java.io.ObjectInput;
  46 import java.io.ObjectOutput;
  47 import java.io.Serializable;
  48
  49 /**
  50  * Represents the object identifier, unique for the host that generated it.
  51  * The ObjID contains inside the integer object identifier that, if needed,
  52  * may indicated that this is a reference to one of the well known objects
  53  * on that host (registry, activator or dgc) and the {@link UID} that
  54  * ensures uniqueness.
  55  */
  56 public final class ObjID
  57     implements Serializable
  58 {
  59
  60   /**
  61    * Use serial version uid for interoperability.
  62    */
  63   static final long serialVersionUID = - 6386392263968365220L;
  64
  65   /**
  66    * The object counter, which value is assigned when creating the ordinary
  67    * objects without the known object id. The counter is incremented each time
  68    * the new ObjID is constructed.
  69    */
  70   private static long next = 0x8000000000000000L;
  71
  72   /**
  73    * The object to put the lock on when incrementing {@link #next}
  74    */
  75   private static final Object lock = ObjID.class;
  76
  77   /**
  78    * Defines the ID of the naming service.
  79    */
  80   public static final int REGISTRY_ID = 0;
  81
  82   /**
  83    * Defines the ID of the activator.
  84    */
  85   public static final int ACTIVATOR_ID = 1;
  86
  87   /**
  88    * Defines the ID of the distributed garbage collector.
  89    */
  90   public static final int DGC_ID = 2;
  91
  92   /**
  93    * The object Id (either well-known value or the value of the incrementing
  94    * object counter.
  95    */
  96   long objNum;
  97
  98   /**
  99    * 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 }