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 java.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ java/applet/AudioClip.java

/*
 * Copyright (c) 1995, 1997, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.applet;

/**
 * The <code>AudioClip</code> interface is a simple abstraction for
 * playing a sound clip. Multiple <code>AudioClip</code> items can be
 * playing at the same time, and the resulting sound is mixed
 * together to produce a composite.
 *
 * @author      Arthur van Hoff
 * @since       JDK1.0
 */
public interface AudioClip {
    /**
     * Starts playing this audio clip. Each time this method is called,
     * the clip is restarted from the beginning.
     */
    void play();

    /**
     * Starts playing this audio clip in a loop.
     */
    void loop();

    /**
     * Stops playing this audio clip.
     */
    void stop();
}

⏎ java/applet/AudioClip.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - javax.* Package Source Code

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)