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/beans/AppletInitializer.java

/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.beans;

import java.applet.Applet;

import java.beans.beancontext.BeanContext;

/**
 * <p>
 * This interface is designed to work in collusion with java.beans.Beans.instantiate.
 * The interface is intended to provide mechanism to allow the proper
 * initialization of JavaBeans that are also Applets, during their
 * instantiation by java.beans.Beans.instantiate().
 * </p>
 *
 * @see java.beans.Beans#instantiate
 *
 * @since 1.2
 *
 */


public interface AppletInitializer {

    /**
     * <p>
     * If passed to the appropriate variant of java.beans.Beans.instantiate
     * this method will be called in order to associate the newly instantiated
     * Applet (JavaBean) with its AppletContext, AppletStub, and Container.
     * </p>
     * <p>
     * Conformant implementations shall:
     * <ol>
     * <li> Associate the newly instantiated Applet with the appropriate
     * AppletContext.
     *
     * <li> Instantiate an AppletStub() and associate that AppletStub with
     * the Applet via an invocation of setStub().
     *
     * <li> If BeanContext parameter is null, then it shall associate the
     * Applet with its appropriate Container by adding that Applet to its
     * Container via an invocation of add(). If the BeanContext parameter is
     * non-null, then it is the responsibility of the BeanContext to associate
     * the Applet with its Container during the subsequent invocation of its
     * addChildren() method.
     * </ol>
     *
     * @param newAppletBean  The newly instantiated JavaBean
     * @param bCtxt          The BeanContext intended for this Applet, or
     *                       null.
     */

    void initialize(Applet newAppletBean, BeanContext bCtxt);

    /**
     * <p>
     * Activate, and/or mark Applet active. Implementors of this interface
     * shall mark this Applet as active, and optionally invoke its start()
     * method.
     * </p>
     *
     * @param newApplet  The newly instantiated JavaBean
     */

    void activate(Applet newApplet);
}

⏎ java/beans/AppletInitializer.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)