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/w3c/dom/css/DocumentCSS.java

/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 * Copyright (c) 2000 World Wide Web Consortium,
 * (Massachusetts Institute of Technology, Institut National de
 * Recherche en Informatique et en Automatique, Keio University). All
 * Rights Reserved. This program is distributed under the W3C's Software
 * Intellectual Property License. This program is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY; without even
 * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE.
 * See W3C License http://www.w3.org/Consortium/Legal/ for more details.
 */

package org.w3c.dom.css;

import org.w3c.dom.Element;
import org.w3c.dom.stylesheets.DocumentStyle;

/**
 * This interface represents a document with a CSS view.
 * <p> The <code>getOverrideStyle</code> method provides a mechanism through
 * which a DOM author could effect immediate change to the style of an
 * element without modifying the explicitly linked style sheets of a
 * document or the inline style of elements in the style sheets. This style
 * sheet comes after the author style sheet in the cascade algorithm and is
 * called override style sheet. The override style sheet takes precedence
 * over author style sheets. An "!important" declaration still takes
 * precedence over a normal declaration. Override, author, and user style
 * sheets all may contain "!important" declarations. User "!important" rules
 * take precedence over both override and author "!important" rules, and
 * override "!important" rules take precedence over author "!important"
 * rules.
 * <p> The expectation is that an instance of the <code>DocumentCSS</code>
 * interface can be obtained by using binding-specific casting methods on an
 * instance of the <code>Document</code> interface.
 * <p>See also the <a href='http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113'>Document Object Model (DOM) Level 2 Style Specification</a>.
 * @since DOM Level 2
 */
public interface DocumentCSS extends DocumentStyle {
    /**
     *  This method is used to retrieve the override style declaration for a
     * specified element and a specified pseudo-element.
     * @param elt  The element whose style is to be modified. This parameter
     *   cannot be null.
     * @param pseudoElt  The pseudo-element or <code>null</code> if none.
     * @return  The override style declaration.
     */
    public CSSStyleDeclaration getOverrideStyle(Element elt,
                                                String pseudoElt);

}

⏎ org/w3c/dom/css/DocumentCSS.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

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⇑⇑ FAQ for JDK (Java Development Kit)