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/rmi/server/Operation.java

/*
 * Copyright (c) 1996, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.rmi.server;

/**
 * An <code>Operation</code> contains a description of a Java method.
 * <code>Operation</code> objects were used in JDK1.1 version stubs and
 * skeletons. The <code>Operation</code> class is not needed for 1.2 style
 * stubs (stubs generated with <code>rmic -v1.2</code>); hence, this class
 * is deprecated.
 *
 * @since JDK1.1
 * @deprecated no replacement
 */
@Deprecated
public class Operation {
    private String operation;

    /**
     * Creates a new Operation object.
     * @param op method name
     * @deprecated no replacement
     * @since JDK1.1
     */
    @Deprecated
    public Operation(String op) {
        operation = op;
    }

    /**
     * Returns the name of the method.
     * @return method name
     * @deprecated no replacement
     * @since JDK1.1
     */
    @Deprecated
    public String getOperation() {
        return operation;
    }

    /**
     * Returns the string representation of the operation.
     * @deprecated no replacement
     * @since JDK1.1
     */
    @Deprecated
    public String toString() {
        return operation;
    }
}

⏎ java/rmi/server/Operation.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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