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/sound/sampled/LineUnavailableException.java

/*
 * Copyright (c) 1999, 2002, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.sound.sampled;

/**
 * A <code>LineUnavailableException</code> is an exception indicating that a
 * line cannot be opened because it is unavailable.  This situation
 * arises most commonly when a requested line is already in use
 * by another application.
 *
 * @author Kara Kytle
 * @since 1.3
 */
/*
 * A <code>LinenavailableException</code> is an exception indicating that a
 * line annot be opened because it is unavailable.  This situation
 * arises most commonly when a line is requested when it is already in use
 * by another application.
 *
 * @author Kara Kytle
 */

public class LineUnavailableException extends Exception {

    /**
     * Constructs a <code>LineUnavailableException</code> that has
     * <code>null</code> as its error detail message.
     */
    public LineUnavailableException() {

        super();
    }


    /**
     * Constructs a <code>LineUnavailableException</code> that has
     * the specified detail message.
     *
     * @param message a string containing the error detail message
     */
    public LineUnavailableException(String message) {

        super(message);
    }
}

⏎ javax/sound/sampled/LineUnavailableException.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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)