Java 1.2 How-To/JavaHowTo.iso/3rdParty/jbuilder/unsupported/JDK1.2beta3/SOURCE/SRC.ZIP/java/rmi/server/RemoteObject.java

Java Source | 1998-03-20 | 5.0 KB | 167 lines

/*
 * @(#)RemoteObject.java    1.13 98/03/18
 *
 * Copyright 1996-1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

package java.rmi.server;

import java.rmi.Remote;
import java.rmi.UnmarshalException;
import java.rmi.NoSuchObjectException;

/**
 * The RemoteObject class implements the java.lang.Object behavior for
 * remote objects.  RemoteObject provides the remote semantics of
 * Object by implementing methods for hashCode, equals, and toString.
 */
public abstract class RemoteObject implements Remote, java.io.Serializable {

    transient protected RemoteRef ref;

    /* indicate compatibility with JDK 1.1.x version of class */
    private static final long serialVersionUID = -3215090123894869218L;

    /**
     * Create a remote object.
     */
    protected RemoteObject() {
    ref = null;
    }

    /**
     * Create a remote object, initialized with the specified remote reference.
     */
    protected RemoteObject(RemoteRef newref) {
    ref = newref;
    }

    /**
     * Returns the remote reference for the remote object.
     */
    public RemoteRef getRef()
    {
    return ref;
    }

    /**
     * Returns the stub for the remote object <code>obj</code> passed
     * as a parameter. This operation is only valid <i>after</i>
     * the object has been exported.

     * @return the stub for the remote object, <code>obj</code>.
     * @exception NoSuchObjectException if the stub for the
     * remote object could not be found.
     */
    public static Remote toStub(Remote obj) throws NoSuchObjectException
    {
    if (obj instanceof RemoteStub) {
        return (RemoteStub)obj;
    } else {
        return sun.rmi.transport.ObjectTable.getStub(obj);
    }
    }

    /**
     * Returns a hashcode for a remote object.  Two remote object stubs
     * that refer to the same remote object will have the same hash code
     * (in order to support remote objects as keys in hash tables).
     *
     * @see        java.util.Hashtable
     */
    public int hashCode() {
    return (ref == null) ? super.hashCode() : ref.remoteHashCode();
    }

    /**
     * Compares two remote objects for equality.
     * Returns a boolean that indicates whether this remote object is
     * equivalent to the specified Object. This method is used when a
     * remote object is stored in a hashtable.
     * If the specified Object is not itself an instance of RemoteObject,
     * then this method delegates by returning the result of invoking the
     * <code>equals</code> method of its parameter with this remote object
     * as the argument.
     * @param    obj    the Object to compare with
     * @return    true if these Objects are equal; false otherwise.
     * @see        java.util.Hashtable
     */
    public boolean equals(Object obj) {
    if (obj instanceof RemoteObject) {
        if (ref == null) {
        return obj == this;
        } else {
        return ref.remoteEquals(((RemoteObject)obj).ref);
        }
    } else if (obj != null) {
        /*
         * Fix for 4099660: if object is not an instance of RemoteObject,
         * use the result of its equals method, to support symmetry is a
         * remote object implementation class that does not extend
         * RemoteObject wishes to support equality with its stub objects.
         */
        return obj.equals(this);
    } else {
        return false;
    }
    }

    /**
     * Returns a String that represents the value of this remote object.
     */
    public String toString()
    {
    String classname = this.getClass().getName();
    return (ref == null) ? classname :
        classname + "[" +ref.remoteToString() + "]";
    }


    /**
     * writeObject for object serialization. Writes out the class name of
     * the remote reference and delegates to the reference to write out
     * its representation.
     */
    private void writeObject(java.io.ObjectOutputStream out)
    throws java.io.IOException, java.lang.ClassNotFoundException
    {
    if (ref == null) {
        throw new java.rmi.MarshalException("Invalid remote object");
    } else {
        out.writeUTF(ref.getRefClass(out));
        ref.writeExternal(out);
    }

    }

    /**
     * readObject for object serialization. Reads in the class name of
     * the remote reference and delegates to the reference to read in
     * its representation.
     */
    private void readObject(java.io.ObjectInputStream in)
    throws java.io.IOException, java.lang.ClassNotFoundException
    {
    try {
        Class refClass = Class.forName(RemoteRef.packagePrefix + "." +
                       in.readUTF());
        ref = (RemoteRef)refClass.newInstance();
        ref.readExternal(in);
    } catch (InstantiationException e) {
        throw new UnmarshalException("Unable to create remote reference",
                     e);
    } catch (IllegalAccessException e) {
        throw new UnmarshalException("Illegal access creating remote reference");
    }
    }

}