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/CosNaming/NamingContext.java

package org.omg.CosNaming;


/**
* org/omg/CosNaming/NamingContext.java .
* Generated by the IDL-to-Java compiler (portable), version "3.2"
* from c:/re/workspace/8-2-build-windows-amd64-cygwin/jdk8u191/11896/corba/src/share/classes/org/omg/CosNaming/nameservice.idl
* Saturday, October 6, 2018 9:30:40 AM PDT
*/


/** 
 * A naming context is an object that contains a set of name bindings in 
 * which each name is unique. Different names can be bound to an object 
 * in the same or different contexts at the same time. <p>
 * 
 * See <a href="http://www.omg.org/technology/documents/formal/naming_service.htm">
 * CORBA COS 
 * Naming Specification.</a>
 */
public interface NamingContext extends NamingContextOperations, org.omg.CORBA.Object, org.omg.CORBA.portable.IDLEntity 
{
} // interface NamingContext

⏎ org/omg/CosNaming/NamingContext.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)