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/nio/file/FileSystemException.java

/*
 * Copyright (c) 2007, 2009, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
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 *
 *
 *
 *
 *
 *
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 *
 *
 *
 *
 *
 *
 *
 */

package java.nio.file;

import java.io.IOException;

/**
 * Thrown when a file system operation fails on one or two files. This class is
 * the general class for file system exceptions.
 *
 * @since 1.7
 */

public class FileSystemException
    extends IOException
{
    static final long serialVersionUID = -3055425747967319812L;

    private final String file;
    private final String other;

    /**
     * Constructs an instance of this class. This constructor should be used
     * when an operation involving one file fails and there isn't any additional
     * information to explain the reason.
     *
     * @param   file
     *          a string identifying the file or {@code null} if not known.
     */
    public FileSystemException(String file) {
        super((String)null);
        this.file = file;
        this.other = null;
    }

    /**
     * Constructs an instance of this class. This constructor should be used
     * when an operation involving two files fails, or there is additional
     * information to explain the reason.
     *
     * @param   file
     *          a string identifying the file or {@code null} if not known.
     * @param   other
     *          a string identifying the other file or {@code null} if there
     *          isn't another file or if not known
     * @param   reason
     *          a reason message with additional information or {@code null}
     */
    public FileSystemException(String file, String other, String reason) {
        super(reason);
        this.file = file;
        this.other = other;
    }

    /**
     * Returns the file used to create this exception.
     *
     * @return  the file (can be {@code null})
     */
    public String getFile() {
        return file;
    }

    /**
     * Returns the other file used to create this exception.
     *
     * @return  the other file (can be {@code null})
     */
    public String getOtherFile() {
        return other;
    }

    /**
     * Returns the string explaining why the file system operation failed.
     *
     * @return  the string explaining why the file system operation failed
     */
    public String getReason() {
        return super.getMessage();
    }

    /**
     * Returns the detail message string.
     */
    @Override
    public String getMessage() {
        if (file == null && other == null)
            return getReason();
        StringBuilder sb = new StringBuilder();
        if (file != null)
            sb.append(file);
        if (other != null) {
            sb.append(" -> ");
            sb.append(other);
        }
        if (getReason() != null) {
            sb.append(": ");
            sb.append(getReason());
        }
        return sb.toString();
    }
}

⏎ java/nio/file/FileSystemException.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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