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/RemoteStub.java

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

/**
 * The {@code RemoteStub} class is the common superclass of
 * statically generated client
 * stubs and provides the framework to support a wide range of remote
 * reference semantics.  Stub objects are surrogates that support
 * exactly the same set of remote interfaces defined by the actual
 * implementation of the remote object.
 *
 * @author  Ann Wollrath
 * @since   JDK1.1
 *
 * @deprecated Statically generated stubs are deprecated, since
 * stubs are generated dynamically. See {@link UnicastRemoteObject}
 * for information about dynamic stub generation.
 */
@Deprecated
abstract public class RemoteStub extends RemoteObject {

    /** indicate compatibility with JDK 1.1.x version of class */
    private static final long serialVersionUID = -1585587260594494182L;

    /**
     * Constructs a {@code RemoteStub}.
     */
    protected RemoteStub() {
        super();
    }

    /**
     * Constructs a {@code RemoteStub} with the specified remote
     * reference.
     *
     * @param ref the remote reference
     * @since JDK1.1
     */
    protected RemoteStub(RemoteRef ref) {
        super(ref);
    }

    /**
     * Throws {@link UnsupportedOperationException}.
     *
     * @param stub the remote stub
     * @param ref the remote reference
     * @throws UnsupportedOperationException always
     * @since JDK1.1
     * @deprecated No replacement.  The {@code setRef} method
     * was intended for setting the remote reference of a remote
     * stub. This is unnecessary, since {@code RemoteStub}s can be created
     * and initialized with a remote reference through use of
     * the {@link #RemoteStub(RemoteRef)} constructor.
     */
    @Deprecated
    protected static void setRef(RemoteStub stub, RemoteRef ref) {
        throw new UnsupportedOperationException();
    }
}

⏎ java/rmi/server/RemoteStub.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

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)