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/jmx/snmp/internal/SnmpTools.java

/*
 * Copyright (c) 2001, 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package com.sun.jmx.snmp.internal;

import com.sun.jmx.snmp.SnmpDefinitions;
/**
 * Utility class used to deal with various data representations.
 * <p><b>This API is a Sun Microsystems internal API  and is subject
 * to change without notice.</b></p>
 * @since 1.5
 */
public class SnmpTools implements SnmpDefinitions {

    /**
     * Translates a binary representation in an ASCII one. The returned string is an hexadecimal string starting with 0x.
     * @param data Binary to translate.
     * @return Translated binary.
     */
    static public String binary2ascii(byte[] data, int length)
    {
        if(data == null) return null;
        final int size = (length * 2) + 2;
        byte[] asciiData = new byte[size];
        asciiData[0] = (byte) '0';
        asciiData[1] = (byte) 'x';
        for (int i=0; i < length; i++) {
            int j = i*2;
            int v = (data[i] & 0xf0);
            v = v >> 4;
            if (v < 10)
                asciiData[j+2] = (byte) ('0' + v);
            else
                asciiData[j+2] = (byte) ('A' + (v - 10));
            v = ((data[i] & 0xf));
            if (v < 10)
                asciiData[j+1+2] = (byte) ('0' + v);
            else
                asciiData[j+1+2] = (byte) ('A' + (v - 10));
        }
        return new String(asciiData);
    }

    /**
     * Translates a binary representation in an ASCII one. The returned string is an hexadecimal string starting with 0x.
     * @param data Binary to translate.
     * @return Translated binary.
     */
    static public String binary2ascii(byte[] data)
    {
        return binary2ascii(data, data.length);
    }
    /**
     * Translates a stringified representation in a binary one. The passed string is an hexadecimal one starting with 0x.
     * @param str String to translate.
     * @return Translated string.
     */
    static public byte[] ascii2binary(String str) {
        if(str == null) return null;
        String val = str.substring(2);

        int size = val.length();
        byte []buf = new byte[size/2];
        byte []p = val.getBytes();

        for(int i = 0; i < (size / 2); i++)
        {
            int j = i * 2;
            byte v = 0;
            if (p[j] >= '0' && p[j] <= '9') {
                v = (byte) ((p[j] - '0') << 4);
            }
            else if (p[j] >= 'a' && p[j] <= 'f') {
                v = (byte) ((p[j] - 'a' + 10) << 4);
            }
            else if (p[j] >= 'A' && p[j] <= 'F') {
                v = (byte) ((p[j] - 'A' + 10) << 4);
            }
            else
                throw new Error("BAD format :" + str);

            if (p[j+1] >= '0' && p[j+1] <= '9') {
                //System.out.println("ascii : " + p[j+1]);
                v += (p[j+1] - '0');
                //System.out.println("binary : " + v);
            }
            else if (p[j+1] >= 'a' && p[j+1] <= 'f') {
                //System.out.println("ascii : " + p[j+1]);
                v += (p[j+1] - 'a' + 10);
                //System.out.println("binary : " + v+1);
            }
            else if (p[j+1] >= 'A' && p[j+1] <= 'F') {
                //System.out.println("ascii : " + p[j+1]);
                v += (p[j+1] - 'A' + 10);
                //System.out.println("binary : " + v);
            }
            else
                throw new Error("BAD format :" + str);

            buf[i] = v;
        }
        return buf;
    }
}

⏎ com/sun/jmx/snmp/internal/SnmpTools.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)