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/sql/SQLType.java

/*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.sql;

/**
 * An object that is used to identify a generic SQL type, called a JDBC type or
 * a vendor specific data type.
 *
 * @since 1.8
 */
public interface SQLType {

    /**
     * Returns the {@code SQLType} name that represents a SQL data type.
     *
     * @return The name of this {@code SQLType}.
     */
    String getName();

    /**
     * Returns the name of the vendor that supports this data type. The value
     * returned typically is the package name for this vendor.
     *
     * @return The name of the vendor for this data type
     */
    String getVendor();

    /**
     * Returns the vendor specific type number for the data type.
     *
     * @return An Integer representing the vendor specific data type
     */
    Integer getVendorTypeNumber();
}

⏎ java/sql/SQLType.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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