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/print/attribute/Attribute.java

/*
 * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package javax.print.attribute;

import java.io.Serializable;

/**
 * Interface Attribute is the base interface implemented by any and every
 * printing attribute class to indicate that the class represents a
 * printing attribute. All printing attributes are serializable.
 * <P>
 *
 * @author  David Mendenhall
 * @author  Alan Kaminsky
 */
public interface Attribute extends Serializable {

  /**
   * Get the printing attribute class which is to be used as the "category"
   * for this printing attribute value when it is added to an attribute set.
   *
   * @return  Printing attribute class (category), an instance of class
   *          {@link java.lang.Class java.lang.Class}.
   */
  public Class<? extends Attribute> getCategory();

  /**
   * Get the name of the category of which this attribute value is an
   * instance.
   * <P>
   * <I>Note:</I> This method is intended to provide a default, nonlocalized
   * string for the attribute's category. If two attribute objects return the
   * same category from the <CODE>getCategory()</CODE> method, they should
   * return the same name from the <CODE>getName()</CODE> method.
   *
   * @return  Attribute category name.
   */
  public String getName();

}

⏎ javax/print/attribute/Attribute.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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