JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the java.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ java/rmi/server/ServerRef.java

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.rmi.server;

import java.rmi.*;

/**
 * A ServerRef represents the server-side handle for a remote object
 * implementation.
 *
 * @author  Ann Wollrath
 * @since   JDK1.1
 * @deprecated No replacement. This interface is unused and is obsolete.
 */
@Deprecated
public interface ServerRef extends RemoteRef {

    /** indicate compatibility with JDK 1.1.x version of class. */
    static final long serialVersionUID = -4557750989390278438L;

    /**
     * Creates a client stub object for the supplied Remote object.
     * If the call completes successfully, the remote object should
     * be able to accept incoming calls from clients.
     * @param obj the remote object implementation
     * @param data information necessary to export the object
     * @return the stub for the remote object
     * @exception RemoteException if an exception occurs attempting
     * to export the object (e.g., stub class could not be found)
     * @since JDK1.1
     */
    RemoteStub exportObject(Remote obj, Object data)
        throws RemoteException;

    /**
     * Returns the hostname of the current client.  When called from a
     * thread actively handling a remote method invocation the
     * hostname of the client is returned.
     * @return the client's host name
     * @exception ServerNotActiveException if called outside of servicing
     * a remote method invocation
     * @since JDK1.1
     */
    String getClientHost() throws ServerNotActiveException;
}

⏎ java/rmi/server/ServerRef.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - javax.* Package Source Code

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