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/lang/model/element/UnknownElementException.java

/*
 * Copyright (c) 2005, 2009, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package javax.lang.model.element;

import javax.lang.model.UnknownEntityException;

/**
 * Indicates that an unknown kind of element was encountered.  This
 * can occur if the language evolves and new kinds of elements are
 * added to the {@code Element} hierarchy.  May be thrown by an
 * {@linkplain ElementVisitor element visitor} to indicate that the
 * visitor was created for a prior version of the language.
 *
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ahé
 * @see ElementVisitor#visitUnknown
 * @since 1.6
 */
public class UnknownElementException extends UnknownEntityException {

    private static final long serialVersionUID = 269L;

    private transient Element element;
    private transient Object parameter;

    /**
     * Creates a new {@code UnknownElementException}.  The {@code p}
     * parameter may be used to pass in an additional argument with
     * information about the context in which the unknown element was
     * encountered; for example, the visit methods of {@link
     * ElementVisitor} may pass in their additional parameter.
     *
     * @param e the unknown element, may be {@code null}
     * @param p an additional parameter, may be {@code null}
     */
    public UnknownElementException(Element e, Object p) {
        super("Unknown element: " + e);
        element = e;
        this.parameter = p;
    }

    /**
     * Returns the unknown element.
     * The value may be unavailable if this exception has been
     * serialized and then read back in.
     *
     * @return the unknown element, or {@code null} if unavailable
     */
    public Element getUnknownElement() {
        return element;
    }

    /**
     * Returns the additional argument.
     *
     * @return the additional argument
     */
    public Object getArgument() {
        return parameter;
    }
}

⏎ javax/lang/model/element/UnknownElementException.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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