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/NotificationListener.java

/*
 * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package javax.management;


/**
 * Should be implemented by an object that wants to receive notifications.
 *
 * @since 1.5
 */
public interface NotificationListener extends java.util.EventListener   {

    /**
    * Invoked when a JMX notification occurs.
    * The implementation of this method should return as soon as possible, to avoid
    * blocking its notification broadcaster.
    *
    * @param notification The notification.
    * @param handback An opaque object which helps the listener to associate
    * information regarding the MBean emitter. This object is passed to the
    * addNotificationListener call and resent, without modification, to the
    * listener.
    */
    public void handleNotification(Notification notification, Object handback);
}

⏎ javax/management/NotificationListener.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

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