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/Skeleton.java

/*
 * Copyright (c) 1996, 2004, 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.Remote;

/**
 * The <code>Skeleton</code> interface is used solely by the RMI
 * implementation.
 *
 * <p> Every version 1.1 (and version 1.1 compatible skeletons generated in
 * 1.2 using <code>rmic -vcompat</code>) skeleton class generated by the rmic
 * stub compiler implements this interface. A skeleton for a remote object is
 * a server-side entity that dispatches calls to the actual remote object
 * implementation.
 *
 * @author  Ann Wollrath
 * @since   JDK1.1
 * @deprecated no replacement.  Skeletons are no longer required for remote
 * method calls in the Java 2 platform v1.2 and greater.
 */
@Deprecated
public interface Skeleton {
    /**
     * Unmarshals arguments, calls the actual remote object implementation,
     * and marshals the return value or any exception.
     *
     * @param obj remote implementation to dispatch call to
     * @param theCall object representing remote call
     * @param opnum operation number
     * @param hash stub/skeleton interface hash
     * @exception java.lang.Exception if a general exception occurs.
     * @since JDK1.1
     * @deprecated no replacement
     */
    @Deprecated
    void dispatch(Remote obj, RemoteCall theCall, int opnum, long hash)
        throws Exception;

    /**
     * Returns the operations supported by the skeleton.
     * @return operations supported by skeleton
     * @since JDK1.1
     * @deprecated no replacement
     */
    @Deprecated
    Operation[] getOperations();
}

⏎ java/rmi/server/Skeleton.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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