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/DOMLocator.java

/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 * Copyright (c) 2004 World Wide Web Consortium,
 *
 * (Massachusetts Institute of Technology, European Research Consortium for
 * Informatics and Mathematics, Keio University). All Rights Reserved. This
 * work is distributed under the W3C(r) Software License [1] 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.
 *
 * [1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
 */

package org.w3c.dom;

/**
 * <code>DOMLocator</code> is an interface that describes a location (e.g.
 * where an error occurred).
 * <p>See also the <a href='http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407'>Document Object Model (DOM) Level 3 Core Specification</a>.
 * @since DOM Level 3
 */
public interface DOMLocator {
    /**
     * The line number this locator is pointing to, or <code>-1</code> if
     * there is no column number available.
     */
    public int getLineNumber();

    /**
     * The column number this locator is pointing to, or <code>-1</code> if
     * there is no column number available.
     */
    public int getColumnNumber();

    /**
     * The byte offset into the input source this locator is pointing to or
     * <code>-1</code> if there is no byte offset available.
     */
    public int getByteOffset();

    /**
     * The UTF-16, as defined in [Unicode] and Amendment 1 of [ISO/IEC 10646], offset into the input source this locator is pointing to or
     * <code>-1</code> if there is no UTF-16 offset available.
     */
    public int getUtf16Offset();

    /**
     * The node this locator is pointing to, or <code>null</code> if no node
     * is available.
     */
    public Node getRelatedNode();

    /**
     * The URI this locator is pointing to, or <code>null</code> if no URI is
     * available.
     */
    public String getUri();

}

⏎ org/w3c/dom/DOMLocator.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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)