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/peer/KeyboardFocusManagerPeer.java

/*
 * Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.awt.peer;

import java.awt.Component;
import java.awt.Window;

/**
 * The native peer interface for {@link KeyboardFocusManager}.
 */
public interface KeyboardFocusManagerPeer {

    /**
     * Sets the window that should become the focused window.
     *
     * @param win the window that should become the focused window
     *
     */
    void setCurrentFocusedWindow(Window win);

    /**
     * Returns the currently focused window.
     *
     * @return the currently focused window
     *
     * @see KeyboardFocusManager#getNativeFocusedWindow()
     */
    Window getCurrentFocusedWindow();

    /**
     * Sets the component that should become the focus owner.
     *
     * @param comp the component to become the focus owner
     *
     * @see KeyboardFocusManager#setNativeFocusOwner(Component)
     */
    void setCurrentFocusOwner(Component comp);

    /**
     * Returns the component that currently owns the input focus.
     *
     * @return the component that currently owns the input focus
     *
     * @see KeyboardFocusManager#getNativeFocusOwner()
     */
    Component getCurrentFocusOwner();

    /**
     * Clears the current global focus owner.
     *
     * @param activeWindow
     *
     * @see KeyboardFocusManager#clearGlobalFocusOwner()
     */
    void clearGlobalFocusOwner(Window activeWindow);

}

⏎ java/awt/peer/KeyboardFocusManagerPeer.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

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