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/DomainManager.java

/*
 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package org.omg.CORBA;

/** Provides mechanisms for establishing and navigating relationships to
 *  superior and subordinate domains, as well as for creating and accessing
 *  policies. The <tt>DomainManager</tt> has associated with it the policy
 *  objects for a
 *  particular domain. The domain manager also records the membership of
 *  the domain and provides the means to add and remove members. The domain
 *  manager is itself a member of a domain, possibly the domain it manages.
 *  The domain manager provides mechanisms for establishing and navigating
 *  relationships to superior and subordinate domains and
 *  creating and accessing policies.
 */

public interface DomainManager extends DomainManagerOperations,
    org.omg.CORBA.Object, org.omg.CORBA.portable.IDLEntity
{
}

⏎ org/omg/CORBA/DomainManager.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)