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/rmi/RMISecurityException.java

/*
 * Copyright (c) 1996, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package java.rmi;

/**
 * An <code>RMISecurityException</code> signals that a security exception
 * has occurred during the execution of one of
 * <code>java.rmi.RMISecurityManager</code>'s methods.
 *
 * @author  Roger Riggs
 * @since   JDK1.1
 * @deprecated Use {@link java.lang.SecurityException} instead.
 * Application code should never directly reference this class, and
 * <code>RMISecurityManager</code> no longer throws this subclass of
 * <code>java.lang.SecurityException</code>.
 */
@Deprecated
public class RMISecurityException extends java.lang.SecurityException {

    /* indicate compatibility with JDK 1.1.x version of class */
     private static final long serialVersionUID = -8433406075740433514L;

    /**
     * Construct an <code>RMISecurityException</code> with a detail message.
     * @param name the detail message
     * @since JDK1.1
     * @deprecated no replacement
     */
    @Deprecated
    public RMISecurityException(String name) {
        super(name);
    }

    /**
     * Construct an <code>RMISecurityException</code> with a detail message.
     * @param name the detail message
     * @param arg ignored
     * @since JDK1.1
     * @deprecated no replacement
     */
    @Deprecated
    public RMISecurityException(String name, String arg) {
        this(name);
    }
}

⏎ java/rmi/RMISecurityException.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)