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 org.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ org/omg/CORBA/portable/UnknownException.java

/*
 * Copyright (c) 1998, 1999, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
 * Licensed Materials - Property of IBM
 * RMI-IIOP v1.0
 * Copyright IBM Corp. 1998 1999  All Rights Reserved
 *
 */

package org.omg.CORBA.portable;
/**
 * The org.omg.CORBA.portable.UnknownException is used for reporting
 * unknown exceptions between ties and ORBs and between ORBs and stubs.
 * It provides a Java representation of an UNKNOWN system exception
 * that has an UnknownExceptionInfo service context.
 * If the CORBA system exception org.omg.CORBA.portable.UnknownException
 * is thrown, then the stub does one of the following:
 * (1) Translates it to org.omg.CORBA.UNKNOWN.
 * (2) Translates it to the nested exception that the UnknownException contains.
 * (3) Passes it on directly to the user.
 */
public class UnknownException extends org.omg.CORBA.SystemException {
    /**
     * A throwable--the original exception that was wrapped in a CORBA
     * UnknownException.
     */
    public Throwable originalEx;
    /**
     * Constructs an UnknownException object.
     * @param ex a Throwable object--to be wrapped in this exception.
     */
    public UnknownException(Throwable ex) {
        super("", 0, org.omg.CORBA.CompletionStatus.COMPLETED_MAYBE);
        originalEx = ex;
    }
}

⏎ org/omg/CORBA/portable/UnknownException.java

Or download all of them as a single archive file:

File name: jre-rt-org-1.8.0_191-src.zip
File size: 951125 bytes
Release date: 2018-10-28
Download 

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

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)