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/beans/MethodRef.java

/*
 * Copyright (c) 2013, 2016, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.beans;

import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Method;

import static sun.reflect.misc.ReflectUtil.isPackageAccessible;

final class MethodRef {
    private String signature;
    private SoftReference<Method> methodRef;
    private WeakReference<Class<?>> typeRef;

    void set(Method method) {
        if (method == null) {
            this.signature = null;
            this.methodRef = null;
            this.typeRef = null;
        }
        else {
            this.signature = method.toGenericString();
            this.methodRef = new SoftReference<>(method);
            this.typeRef = new WeakReference<Class<?>>(method.getDeclaringClass());
        }
    }

    boolean isSet() {
        return this.methodRef != null;
    }

    Method get() {
        if (this.methodRef == null) {
            return null;
        }
        Method method = this.methodRef.get();
        if (method == null) {
            method = find(this.typeRef.get(), this.signature);
            if (method == null) {
                this.signature = null;
                this.methodRef = null;
                this.typeRef = null;
                return null;
            }
            this.methodRef = new SoftReference<>(method);
        }
        return isPackageAccessible(method.getDeclaringClass()) ? method : null;
    }

    private static Method find(Class<?> type, String signature) {
        if (type != null) {
            for (Method method : type.getMethods()) {
                if (type.equals(method.getDeclaringClass())) {
                    if (method.toGenericString().equals(signature)) {
                        return method;
                    }
                }
            }
        }
        return null;
    }
}

⏎ java/beans/MethodRef.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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