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

⏎ javax/swing/colorchooser/CenterLayout.java

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

package javax.swing.colorchooser;

import java.awt.*;
import java.io.*;


/**
  * Center-positioning layout manager.
  * @author Tom Santos
  * @author Steve Wilson
  */
class CenterLayout implements LayoutManager, Serializable {
    public void addLayoutComponent(String name, Component comp) { }
    public void removeLayoutComponent(Component comp) { }

    public Dimension preferredLayoutSize( Container container ) {
        Component c = container.getComponent( 0 );
        if ( c != null ) {
            Dimension size = c.getPreferredSize();
            Insets insets = container.getInsets();
            size.width += insets.left + insets.right;
            size.height += insets.top + insets.bottom;
            return size;
        }
        else {
            return new Dimension( 0, 0 );
        }
    }

    public Dimension minimumLayoutSize(Container cont) {
        return preferredLayoutSize(cont);
    }

    public void layoutContainer(Container container) {
        try {
           Component c = container.getComponent( 0 );

           c.setSize( c.getPreferredSize() );
           Dimension size = c.getSize();
           Dimension containerSize = container.getSize();
           Insets containerInsets = container.getInsets();
           containerSize.width -= containerInsets.left + containerInsets.right;
           containerSize.height -= containerInsets.top + containerInsets.bottom;
           int componentLeft = (containerSize.width / 2) - (size.width / 2);
           int componentTop = (containerSize.height / 2) - (size.height / 2);
           componentLeft += containerInsets.left;
           componentTop += containerInsets.top;

            c.setBounds( componentLeft, componentTop, size.width, size.height );
         }
         catch( Exception e ) {
         }
    }
}

⏎ javax/swing/colorchooser/CenterLayout.java

Or download all of them as a single archive file:

File name: jre-rt-javax-1.8.0_191-src.zip
File size: 5381005 bytes
Release date: 2018-10-28
Download 

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

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

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