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/lang/management/OperatingSystemMXBean.java

/*
 * Copyright (c) 2003, 2008, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.lang.management;

/**
 * The management interface for the operating system on which
 * the Java virtual machine is running.
 *
 * <p> A Java virtual machine has a single instance of the implementation
 * class of this interface.  This instance implementing this interface is
 * an <a href="ManagementFactory.html#MXBean">MXBean</a>
 * that can be obtained by calling
 * the {@link ManagementFactory#getOperatingSystemMXBean} method or
 * from the {@link ManagementFactory#getPlatformMBeanServer
 * platform <tt>MBeanServer</tt>} method.
 *
 * <p>The <tt>ObjectName</tt> for uniquely identifying the MXBean for
 * the operating system within an MBeanServer is:
 * <blockquote>
 *    {@link ManagementFactory#OPERATING_SYSTEM_MXBEAN_NAME
 *      <tt>java.lang:type=OperatingSystem</tt>}
 * </blockquote>
 *
 * It can be obtained by calling the
 * {@link PlatformManagedObject#getObjectName} method.
 *
 * <p> This interface defines several convenient methods for accessing
 * system properties about the operating system on which the Java
 * virtual machine is running.
 *
 * @see ManagementFactory#getPlatformMXBeans(Class)
 * @see <a href="../../../javax/management/package-summary.html">
 *      JMX Specification.</a>
 * @see <a href="package-summary.html#examples">
 *      Ways to Access MXBeans</a>
 *
 * @author  Mandy Chung
 * @since   1.5
 */
public interface OperatingSystemMXBean extends PlatformManagedObject {
    /**
     * Returns the operating system name.
     * This method is equivalent to <tt>System.getProperty("os.name")</tt>.
     *
     * @return the operating system name.
     *
     * @throws  java.lang.SecurityException
     *     if a security manager exists and its
     *     <code>checkPropertiesAccess</code> method doesn't allow access
     *     to this system property.
     * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
     * @see java.lang.System#getProperty
     */
    public String getName();

    /**
     * Returns the operating system architecture.
     * This method is equivalent to <tt>System.getProperty("os.arch")</tt>.
     *
     * @return the operating system architecture.
     *
     * @throws  java.lang.SecurityException
     *     if a security manager exists and its
     *     <code>checkPropertiesAccess</code> method doesn't allow access
     *     to this system property.
     * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
     * @see java.lang.System#getProperty
     */
    public String getArch();

    /**
     * Returns the operating system version.
     * This method is equivalent to <tt>System.getProperty("os.version")</tt>.
     *
     * @return the operating system version.
     *
     * @throws  java.lang.SecurityException
     *     if a security manager exists and its
     *     <code>checkPropertiesAccess</code> method doesn't allow access
     *     to this system property.
     * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
     * @see java.lang.System#getProperty
     */
    public String getVersion();

    /**
     * Returns the number of processors available to the Java virtual machine.
     * This method is equivalent to the {@link Runtime#availableProcessors()}
     * method.
     * <p> This value may change during a particular invocation of
     * the virtual machine.
     *
     * @return  the number of processors available to the virtual
     *          machine; never smaller than one.
     */
    public int getAvailableProcessors();

    /**
     * Returns the system load average for the last minute.
     * The system load average is the sum of the number of runnable entities
     * queued to the {@linkplain #getAvailableProcessors available processors}
     * and the number of runnable entities running on the available processors
     * averaged over a period of time.
     * The way in which the load average is calculated is operating system
     * specific but is typically a damped time-dependent average.
     * <p>
     * If the load average is not available, a negative value is returned.
     * <p>
     * This method is designed to provide a hint about the system load
     * and may be queried frequently.
     * The load average may be unavailable on some platform where it is
     * expensive to implement this method.
     *
     * @return the system load average; or a negative value if not available.
     *
     * @since 1.6
     */
    public double getSystemLoadAverage();
}

⏎ java/lang/management/OperatingSystemMXBean.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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