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/imageio/plugins/jpeg/DRIMarkerSegment.java

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

package com.sun.imageio.plugins.jpeg;

import javax.imageio.metadata.IIOInvalidTreeException;
import javax.imageio.metadata.IIOMetadataNode;
import javax.imageio.stream.ImageOutputStream;

import java.io.IOException;

import org.w3c.dom.Node;

/**
     * A DRI (Define Restart Interval) marker segment.
     */
class DRIMarkerSegment extends MarkerSegment {
    /**
     * Restart interval, or 0 if none is specified.
     */
    int restartInterval = 0;

    DRIMarkerSegment(JPEGBuffer buffer)
        throws IOException {
        super(buffer);
        restartInterval = (buffer.buf[buffer.bufPtr++] & 0xff) << 8;
        restartInterval |= buffer.buf[buffer.bufPtr++] & 0xff;
        buffer.bufAvail -= length;
    }

    DRIMarkerSegment(Node node) throws IIOInvalidTreeException {
        super(JPEG.DRI);
        updateFromNativeNode(node, true);
    }

    IIOMetadataNode getNativeNode() {
        IIOMetadataNode node = new IIOMetadataNode("dri");
        node.setAttribute("interval", Integer.toString(restartInterval));
        return node;
    }

    void updateFromNativeNode(Node node, boolean fromScratch)
        throws IIOInvalidTreeException {
        restartInterval = getAttributeValue(node, null, "interval",
                                            0, 65535, true);
    }

    /**
     * Writes the data for this segment to the stream in
     * valid JPEG format.
     */
    void write(ImageOutputStream ios) throws IOException {
        // We don't write DRI segments; the IJG library does.
    }

    void print() {
        printTag("DRI");
        System.out.println("Interval: "
                           + Integer.toString(restartInterval));
    }
}

⏎ com/sun/imageio/plugins/jpeg/DRIMarkerSegment.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 

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