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/orbutil/LegacyHookGetFields.java

/*
 * Copyright (c) 2001, 2002, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

/*
 */
package com.sun.corba.se.impl.orbutil;

import java.io.*;
import java.util.Hashtable;

class LegacyHookGetFields extends ObjectInputStream.GetField {
    private Hashtable fields = null;

    LegacyHookGetFields(Hashtable fields){
        this.fields = fields;
    }

    /**
     * Get the ObjectStreamClass that describes the fields in the stream.
     */
    public java.io.ObjectStreamClass getObjectStreamClass() {
        return null;
    }

    /**
     * Return true if the named field is defaulted and has no value
     * in this stream.
     */
    public boolean defaulted(String name)
        throws IOException, IllegalArgumentException  {
        return (!fields.containsKey(name));
    }

    /**
     * Get the value of the named boolean field from the persistent field.
     */
    public boolean get(String name, boolean defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Boolean)fields.get(name)).booleanValue();
    }

    /**
     * Get the value of the named char field from the persistent fields.
     */
    public char get(String name, char defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Character)fields.get(name)).charValue();

    }

    /**
     * Get the value of the named byte field from the persistent fields.
     */
    public byte get(String name, byte defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Byte)fields.get(name)).byteValue();

    }

    /**
     * Get the value of the named short field from the persistent fields.
     */
    public short get(String name, short defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Short)fields.get(name)).shortValue();

    }

    /**
     * Get the value of the named int field from the persistent fields.
     */
    public int get(String name, int defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Integer)fields.get(name)).intValue();

    }

    /**
     * Get the value of the named long field from the persistent fields.
     */
    public long get(String name, long defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Long)fields.get(name)).longValue();

    }

    /**
     * Get the value of the named float field from the persistent fields.
     */
    public float get(String name, float defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return ((Float)fields.get(name)).floatValue();

    }

    /**
     * Get the value of the named double field from the persistent field.
     */
    public double get(String name, double defvalue)
        throws IOException, IllegalArgumentException  {
        if (defaulted(name))
            return defvalue;
        else return ((Double)fields.get(name)).doubleValue();

    }

    /**
     * Get the value of the named Object field from the persistent field.
     */
    public Object get(String name, Object defvalue)
        throws IOException, IllegalArgumentException {
        if (defaulted(name))
            return defvalue;
        else return fields.get(name);

    }

    public String toString(){
        return fields.toString();
    }
}

⏎ com/sun/corba/se/impl/orbutil/LegacyHookGetFields.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)