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/WindowFocusListener.java

/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.awt.event;

import java.util.EventListener;

/**
 * The listener interface for receiving <code>WindowEvents</code>, including
 * <code>WINDOW_GAINED_FOCUS</code> and <code>WINDOW_LOST_FOCUS</code> events.
 * The class that is interested in processing a <code>WindowEvent</code>
 * either implements this interface (and
 * all the methods it contains) or extends the abstract
 * <code>WindowAdapter</code> class (overriding only the methods of interest).
 * The listener object created from that class is then registered with a
 * <code>Window</code>
 * using the <code>Window</code>'s <code>addWindowFocusListener</code> method.
 * When the <code>Window</code>'s
 * status changes by virtue of it being opened, closed, activated, deactivated,
 * iconified, or deiconified, or by focus being transfered into or out of the
 * <code>Window</code>, the relevant method in the listener object is invoked,
 * and the <code>WindowEvent</code> is passed to it.
 *
 * @author David Mendenhall
 *
 * @see WindowAdapter
 * @see WindowEvent
 * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/windowlistener.html">Tutorial: Writing a Window Listener</a>
 *
 * @since 1.4
 */
public interface WindowFocusListener extends EventListener {

    /**
     * Invoked when the Window is set to be the focused Window, which means
     * that the Window, or one of its subcomponents, will receive keyboard
     * events.
     */
    public void windowGainedFocus(WindowEvent e);

    /**
     * Invoked when the Window is no longer the focused Window, which means
     * that keyboard events will no longer be delivered to the Window or any of
     * its subcomponents.
     */
    public void windowLostFocus(WindowEvent e);
}

⏎ java/awt/event/WindowFocusListener.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 

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