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/java/swing/plaf/windows/WindowsPopupMenuSeparatorUI.java

/*
 * Copyright (c) 2004, 2014, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package com.sun.java.swing.plaf.windows;

import java.awt.*;

import javax.swing.*;
import javax.swing.plaf.basic.BasicPopupMenuSeparatorUI;
import javax.swing.plaf.ComponentUI;

import com.sun.java.swing.plaf.windows.TMSchema.Part;
import com.sun.java.swing.plaf.windows.TMSchema.State;
import com.sun.java.swing.plaf.windows.XPStyle.Skin;

/**
 * Windows L&F implementation of PopupMenuSeparatorUI.
 *
 * @author Leif Samuelsson
 * @author Igor Kushnirskiy
 */

public class WindowsPopupMenuSeparatorUI extends BasicPopupMenuSeparatorUI {

    public static ComponentUI createUI(JComponent c) {
        return new WindowsPopupMenuSeparatorUI();
    }

    public void paint(Graphics g, JComponent c) {
        Dimension s = c.getSize();
        XPStyle xp = XPStyle.getXP();
        if (WindowsMenuItemUI.isVistaPainting(xp)) {
            int x = 1;
            Component parent = c.getParent();
            if (parent instanceof JComponent) {
                Object gutterOffsetObject =
                    ((JComponent) parent).getClientProperty(
                        WindowsPopupMenuUI.GUTTER_OFFSET_KEY);
                if (gutterOffsetObject instanceof Integer) {
                    /*
                     * gutter offset is in parent's coordinates.
                     * See comment in
                     * WindowsPopupMenuUI.getTextOffset(JComponent)
                     */
                    x = ((Integer) gutterOffsetObject).intValue() - c.getX();
                    x += WindowsPopupMenuUI.getGutterWidth();
                }
            }
            Skin skin = xp.getSkin(c, Part.MP_POPUPSEPARATOR);
            int skinHeight = skin.getHeight();
            int y = (s.height - skinHeight) / 2;
            skin.paintSkin(g, x, y, s.width - x - 1, skinHeight, State.NORMAL);
        } else {
            int y = s.height / 2;
            g.setColor(c.getForeground());
            g.drawLine(1, y - 1, s.width - 2, y - 1);

            g.setColor(c.getBackground());
            g.drawLine(1, y,     s.width - 2, y);
        }
    }

    public Dimension getPreferredSize(JComponent c) {
        int fontHeight = 0;
        Font font = c.getFont();
        if (font != null) {
            fontHeight = c.getFontMetrics(font).getHeight();
        }

        return new Dimension(0, fontHeight/2 + 2);
    }

}

⏎ com/sun/java/swing/plaf/windows/WindowsPopupMenuSeparatorUI.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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