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

⏎ java/awt/event/KeyAdapter.java

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.awt.event;

/**
 * An abstract adapter class for receiving keyboard events.
 * The methods in this class are empty. This class exists as
 * convenience for creating listener objects.
 * <P>
 * Extend this class to create a <code>KeyEvent</code> listener
 * and override the methods for the events of interest. (If you implement the
 * <code>KeyListener</code> interface, you have to define all of
 * the methods in it. This abstract class defines null methods for them
 * all, so you can only have to define methods for events you care about.)
 * <P>
 * Create a listener object using the extended class and then register it with
 * a component using the component's <code>addKeyListener</code>
 * method. When a key is pressed, released, or typed,
 * the relevant method in the listener object is invoked,
 * and the <code>KeyEvent</code> is passed to it.
 *
 * @author Carl Quinn
 *
 * @see KeyEvent
 * @see KeyListener
 * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html">Tutorial: Writing a Key Listener</a>
 *
 * @since 1.1
 */
public abstract class KeyAdapter implements KeyListener {
    /**
     * Invoked when a key has been typed.
     * This event occurs when a key press is followed by a key release.
     */
    public void keyTyped(KeyEvent e) {}

    /**
     * Invoked when a key has been pressed.
     */
    public void keyPressed(KeyEvent e) {}

    /**
     * Invoked when a key has been released.
     */
    public void keyReleased(KeyEvent e) {}
}

⏎ java/awt/event/KeyAdapter.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

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

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)