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

⏎ javax/management/relation/RelationSupportMBean.java

/*
 * Copyright (c) 2000, 2005, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.management.relation;

/**
 * A RelationSupport object is used internally by the Relation Service to
 * represent simple relations (only roles, no properties or methods), with an
 * unlimited number of roles, of any relation type. As internal representation,
 * it is not exposed to the user.
 * <P>RelationSupport class conforms to the design patterns of standard MBean. So
 * the user can decide to instantiate a RelationSupport object himself as
 * a MBean (as it follows the MBean design patterns), to register it in the
 * MBean Server, and then to add it in the Relation Service.
 * <P>The user can also, when creating his own MBean relation class, have it
 * extending RelationSupport, to retrieve the implementations of required
 * interfaces (see below).
 * <P>It is also possible to have in a user relation MBean class a member
 * being a RelationSupport object, and to implement the required interfaces by
 * delegating all to this member.
 * <P> RelationSupport implements the Relation interface (to be handled by the
 * Relation Service).
 *
 * @since 1.5
 */
public interface RelationSupportMBean
    extends Relation {

    /**
     * Returns an internal flag specifying if the object is still handled by
     * the Relation Service.
     *
     * @return a Boolean equal to {@link Boolean#TRUE} if the object
     * is still handled by the Relation Service and {@link
     * Boolean#FALSE} otherwise.
     */
    public Boolean isInRelationService();

    /**
     * <p>Specifies whether this relation is handled by the Relation
     * Service.</p>
     * <P>BEWARE, this method has to be exposed as the Relation Service will
     * access the relation through its management interface. It is RECOMMENDED
     * NOT to use this method. Using it does not affect the registration of the
     * relation object in the Relation Service, but will provide wrong
     * information about it!
     *
     * @param flag whether the relation is handled by the Relation Service.
     *
     * @exception IllegalArgumentException  if null parameter
     */
    public void setRelationServiceManagementFlag(Boolean flag)
        throws IllegalArgumentException;
}

⏎ javax/management/relation/RelationSupportMBean.java

Or download all of them as a single archive file:

File name: jre-rt-javax-1.8.0_191-src.zip
File size: 5381005 bytes
Release date: 2018-10-28
Download 

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

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)