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/io/FileNotFoundException.java

/*
 * Copyright (c) 1994, 2008, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.io;


/**
 * Signals that an attempt to open the file denoted by a specified pathname
 * has failed.
 *
 * <p> This exception will be thrown by the {@link FileInputStream}, {@link
 * FileOutputStream}, and {@link RandomAccessFile} constructors when a file
 * with the specified pathname does not exist.  It will also be thrown by these
 * constructors if the file does exist but for some reason is inaccessible, for
 * example when an attempt is made to open a read-only file for writing.
 *
 * @author  unascribed
 * @since   JDK1.0
 */

public class FileNotFoundException extends IOException {
    private static final long serialVersionUID = -897856973823710492L;

    /**
     * Constructs a <code>FileNotFoundException</code> with
     * <code>null</code> as its error detail message.
     */
    public FileNotFoundException() {
        super();
    }

    /**
     * Constructs a <code>FileNotFoundException</code> with the
     * specified detail message. The string <code>s</code> can be
     * retrieved later by the
     * <code>{@link java.lang.Throwable#getMessage}</code>
     * method of class <code>java.lang.Throwable</code>.
     *
     * @param   s   the detail message.
     */
    public FileNotFoundException(String s) {
        super(s);
    }

    /**
     * Constructs a <code>FileNotFoundException</code> with a detail message
     * consisting of the given pathname string followed by the given reason
     * string.  If the <code>reason</code> argument is <code>null</code> then
     * it will be omitted.  This private constructor is invoked only by native
     * I/O methods.
     *
     * @since 1.2
     */
    private FileNotFoundException(String path, String reason) {
        super(path + ((reason == null)
                      ? ""
                      : " (" + reason + ")"));
    }

}

⏎ java/io/FileNotFoundException.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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