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

⏎ com/sun/corba/se/impl/io/OptionalDataException.java

/*
 * Copyright (c) 1998, 2002, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

/*
 * Licensed Materials - Property of IBM
 * RMI-IIOP v1.0
 * Copyright IBM Corp. 1998 1999  All Rights Reserved
 *
 */

package com.sun.corba.se.impl.io;

/**
 * Unexpected data appeared in an ObjectInputStream trying to read
 * an Object.
 * This exception occurs when the stream contains primitive data
 * instead of the object expected by readObject.
 * The eof flag in the exception is true to indicate that no more
 * primitive data is available.
 * The count field contains the number of bytes available to read.
 *
 * @author  unascribed
 * @since   JDK1.1
 */
public class OptionalDataException extends java.io.IOException {
    /*
     * Create an <code>OptionalDataException</code> with a length.
     */
    OptionalDataException(int len) {
        eof = false;
        length = len;
    }

    /*
     * Create an <code>OptionalDataException</code> signifing no
     * more primitive data is available.
     */
    OptionalDataException(boolean end) {
        length = 0;
        eof = end;
    }

    /**
     * The number of bytes of primitive data available to be read
     * in the current buffer.
     */
    public int length;

    /**
     * True if there is no more data in the buffered part of the stream.
     */
    public boolean eof;
}

⏎ com/sun/corba/se/impl/io/OptionalDataException.java

Or download all of them as a single archive file:

File name: jre-rt-com-1.8.0_191-src.zip
File size: 8099783 bytes
Release date: 2018-10-28
Download 

⇒ Backup JDK 8 Installation Directory

⇐ JRE 8 rt.jar - org.* Package Source Code

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)