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/print/event/PrintEvent.java

/*
 * Copyright (c) 2000, 2003, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package javax.print.event;

/**
 *
 * Class PrintEvent is the super class of all Print Service API events.
 */

public class PrintEvent extends java.util.EventObject {

    private static final long serialVersionUID = 2286914924430763847L;

    /**
     * Constructs a PrintEvent object.
     * @param source is the source of the event
     * @throws IllegalArgumentException if <code>source</code> is
     *         <code>null</code>.
     */
    public PrintEvent (Object source) {
        super(source);
    }

    /**
     * @return a message describing the event
     */
    public String toString() {
        return ("PrintEvent on " + getSource().toString());
    }

}

⏎ javax/print/event/PrintEvent.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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