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/net/SocketSecrets.java

/*
 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.net;

import java.io.IOException;

class SocketSecrets {

    /* accessed by reflection from jdk.net.Sockets */

    /* obj must be a Socket or ServerSocket */

    private static <T> void setOption(Object obj, SocketOption<T> name, T value) throws IOException {
        SocketImpl impl;

        if (obj instanceof Socket) {
            impl = ((Socket)obj).getImpl();
        } else if (obj instanceof ServerSocket) {
            impl = ((ServerSocket)obj).getImpl();
        } else {
            throw new IllegalArgumentException();
        }
        impl.setOption(name, value);
    }

    private static <T> T getOption(Object obj, SocketOption<T> name) throws IOException {
        SocketImpl impl;

        if (obj instanceof Socket) {
            impl = ((Socket)obj).getImpl();
        } else if (obj instanceof ServerSocket) {
            impl = ((ServerSocket)obj).getImpl();
        } else {
            throw new IllegalArgumentException();
        }
        return impl.getOption(name);
    }

    private static <T> void setOption(DatagramSocket s, SocketOption<T> name, T value) throws IOException {
        s.getImpl().setOption(name, value);
    }

    private static <T> T getOption(DatagramSocket s, SocketOption<T> name) throws IOException {
        return s.getImpl().getOption(name);
    }

}

⏎ java/net/SocketSecrets.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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