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/*
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* Copyright 1996-2006 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Sun designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Sun in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*/
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package java.rmi.server;
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import java.io.DataInput;
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import java.io.DataOutput;
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import java.io.IOException;
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import java.io.ObjectInput;
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import java.io.ObjectOutput;
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import java.io.Serializable;
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import java.security.AccessController;
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import java.security.SecureRandom;
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import java.util.concurrent.atomic.AtomicLong;
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import sun.security.action.GetPropertyAction;
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/**
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* An <code>ObjID</code> is used to identify a remote object exported
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* to an RMI runtime. When a remote object is exported, it is assigned
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* an object identifier either implicitly or explicitly, depending on
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* the API used to export.
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*
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* <p>The {@link #ObjID()} constructor can be used to generate a unique
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* object identifier. Such an <code>ObjID</code> is unique over time
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* with respect to the host it is generated on.
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*
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* The {@link #ObjID(int)} constructor can be used to create a
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* "well-known" object identifier. The scope of a well-known
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* <code>ObjID</code> depends on the RMI runtime it is exported to.
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*
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* <p>An <code>ObjID</code> instance contains an object number (of type
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* <code>long</code>) and an address space identifier (of type
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* {@link UID}). In a unique <code>ObjID</code>, the address space
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* identifier is unique with respect to a given host over time. In a
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* well-known <code>ObjID</code>, the address space identifier is
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* equivalent to one returned by invoking the {@link UID#UID(short)}
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* constructor with the value zero.
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*
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* <p>If the system property <code>java.rmi.server.randomIDs</code>
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* is defined to equal the string <code>"true"</code> (case insensitive),
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* then the {@link #ObjID()} constructor will use a cryptographically
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* strong random number generator to choose the object number of the
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* returned <code>ObjID</code>.
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*
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* @author Ann Wollrath
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* @author Peter Jones
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* @since JDK1.1
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*/
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public final class ObjID implements Serializable {
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/** Object number for well-known <code>ObjID</code> of the registry. */
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public static final int REGISTRY_ID = 0;
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/** Object number for well-known <code>ObjID</code> of the activator. */
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public static final int ACTIVATOR_ID = 1;
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/**
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* Object number for well-known <code>ObjID</code> of
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* the distributed garbage collector.
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*/
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public static final int DGC_ID = 2;
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/** indicate compatibility with JDK 1.1.x version of class */
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private static final long serialVersionUID = -6386392263968365220L;
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private static final AtomicLong nextObjNum = new AtomicLong(0);
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private static final UID mySpace = new UID();
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private static final SecureRandom secureRandom = new SecureRandom();
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/**
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* @serial object number
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* @see #hashCode
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*/
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private final long objNum;
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/**
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* @serial address space identifier (unique to host over time)
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*/
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private final UID space;
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/**
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* Generates a unique object identifier.
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*
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* <p>If the system property <code>java.rmi.server.randomIDs</code>
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* is defined to equal the string <code>"true"</code> (case insensitive),
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* then this constructor will use a cryptographically
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* strong random number generator to choose the object number of the
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* returned <code>ObjID</code>.
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*/
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public ObjID() {
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/*
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* If generating random object numbers, create a new UID to
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* ensure uniqueness; otherwise, use a shared UID because
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* sequential object numbers already ensure uniqueness.
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*/
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if (useRandomIDs()) {
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space = new UID();
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objNum = secureRandom.nextLong();
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} else {
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space = mySpace;
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objNum = nextObjNum.getAndIncrement();
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}
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}
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/**
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* Creates a "well-known" object identifier.
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*
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* <p>An <code>ObjID</code> created via this constructor will not
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* clash with any <code>ObjID</code>s generated via the no-arg
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* constructor.
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*
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* @param objNum object number for well-known object identifier
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*/
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public ObjID(int objNum) {
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space = new UID((short) 0);
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this.objNum = objNum;
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}
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/**
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* Constructs an object identifier given data read from a stream.
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*/
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private ObjID(long objNum, UID space) {
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this.objNum = objNum;
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this.space = space;
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}
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/**
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* Marshals a binary representation of this <code>ObjID</code> to
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* an <code>ObjectOutput</code> instance.
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*
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* <p>Specifically, this method first invokes the given stream's
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* {@link ObjectOutput#writeLong(long)} method with this object
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* identifier's object number, and then it writes its address
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* space identifier by invoking its {@link UID#write(DataOutput)}
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* method with the stream.
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*
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* @param out the <code>ObjectOutput</code> instance to write
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* this <code>ObjID</code> to
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*
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* @throws IOException if an I/O error occurs while performing
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* this operation
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*/
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public void write(ObjectOutput out) throws IOException {
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out.writeLong(objNum);
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space.write(out);
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}
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/**
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* Constructs and returns a new <code>ObjID</code> instance by
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* unmarshalling a binary representation from an
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* <code>ObjectInput</code> instance.
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*
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* <p>Specifically, this method first invokes the given stream's
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* {@link ObjectInput#readLong()} method to read an object number,
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* then it invokes {@link UID#read(DataInput)} with the
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* stream to read an address space identifier, and then it
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* creates and returns a new <code>ObjID</code> instance that
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* contains the object number and address space identifier that
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* were read from the stream.
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*
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* @param in the <code>ObjectInput</code> instance to read
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* <code>ObjID</code> from
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*
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* @return unmarshalled <code>ObjID</code> instance
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*
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* @throws IOException if an I/O error occurs while performing
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* this operation
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*/
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public static ObjID read(ObjectInput in) throws IOException {
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long num = in.readLong();
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UID space = UID.read(in);
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return new ObjID(num, space);
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}
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/**
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* Returns the hash code value for this object identifier, the
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* object number.
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*
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* @return the hash code value for this object identifier
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*/
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public int hashCode() {
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return (int) objNum;
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}
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/**
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* Compares the specified object with this <code>ObjID</code> for
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* equality.
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*
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* This method returns <code>true</code> if and only if the
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* specified object is an <code>ObjID</code> instance with the same
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* object number and address space identifier as this one.
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*
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* @param obj the object to compare this <code>ObjID</code> to
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*
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* @return <code>true</code> if the given object is equivalent to
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* this one, and <code>false</code> otherwise
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*/
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public boolean equals(Object obj) {
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if (obj instanceof ObjID) {
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ObjID id = (ObjID) obj;
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return objNum == id.objNum && space.equals(id.space);
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} else {
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return false;
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}
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}
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/**
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* Returns a string representation of this object identifier.
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*
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* @return a string representation of this object identifier
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*/
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/*
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* The address space identifier is only included in the string
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* representation if it does not denote the local address space
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* (or if the randomIDs property was set).
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*/
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public String toString() {
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return "[" + (space.equals(mySpace) ? "" : space + ", ") +
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objNum + "]";
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}
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private static boolean useRandomIDs() {
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String value = AccessController.doPrivileged(
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new GetPropertyAction("java.rmi.server.randomIDs"));
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return value == null ? true : Boolean.parseBoolean(value);
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}
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}
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