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/imageio/spi/RegisterableService.java

/*
 * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package javax.imageio.spi;

/**
 * An optional interface that may be provided by service provider
 * objects that will be registered with a
 * <code>ServiceRegistry</code>.  If this interface is present,
 * notification of registration and deregistration will be performed.
 *
 * @see ServiceRegistry
 *
 */
public interface RegisterableService {

    /**
     * Called when an object implementing this interface is added to
     * the given <code>category</code> of the given
     * <code>registry</code>.  The object may already be registered
     * under another category or categories.
     *
     * @param registry a <code>ServiceRegistry</code> where this
     * object has been registered.
     * @param category a <code>Class</code> object indicating the
     * registry category under which this object has been registered.
     */
    void onRegistration(ServiceRegistry registry, Class<?> category);

    /**
     * Called when an object implementing this interface is removed
     * from the given <code>category</code> of the given
     * <code>registry</code>.  The object may still be registered
     * under another category or categories.
     *
     * @param registry a <code>ServiceRegistry</code> from which this
     * object is being (wholly or partially) deregistered.
     * @param category a <code>Class</code> object indicating the
     * registry category from which this object is being deregistered.
     */
    void onDeregistration(ServiceRegistry registry, Class<?> category);
}

⏎ javax/imageio/spi/RegisterableService.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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