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/DescriptorAccess.java

/*
 * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
 * @author    IBM Corp.
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 * Copyright IBM Corp. 1999-2000.  All rights reserved.
 */

package javax.management;

/**
 * This interface is used to gain access to descriptors of the Descriptor class
 * which are associated with a JMX component, i.e. MBean, MBeanInfo,
 * MBeanAttributeInfo, MBeanNotificationInfo,
 * MBeanOperationInfo, MBeanParameterInfo.
 * <P>
 * ModelMBeans make extensive use of this interface in ModelMBeanInfo classes.
 *
 * @since 1.5
 */
public interface DescriptorAccess extends DescriptorRead
{
    /**
    * Sets Descriptor (full replace).
    *
    * @param inDescriptor replaces the Descriptor associated with the
    * component implementing this interface. If the inDescriptor is invalid for the
    * type of Info object it is being set for, an exception is thrown.  If the
    * inDescriptor is null, then the Descriptor will revert to its default value
    * which should contain, at a minimum, the descriptor name and descriptorType.
    *
    * @see #getDescriptor
    */
    public void setDescriptor(Descriptor inDescriptor);
}

⏎ javax/management/DescriptorAccess.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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