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/FilterReader.java

/*
 * Copyright (c) 1996, 2005, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.io;


/**
 * Abstract class for reading filtered character streams.
 * The abstract class <code>FilterReader</code> itself
 * provides default methods that pass all requests to
 * the contained stream. Subclasses of <code>FilterReader</code>
 * should override some of these methods and may also provide
 * additional methods and fields.
 *
 * @author      Mark Reinhold
 * @since       JDK1.1
 */

public abstract class FilterReader extends Reader {

    /**
     * The underlying character-input stream.
     */
    protected Reader in;

    /**
     * Creates a new filtered reader.
     *
     * @param in  a Reader object providing the underlying stream.
     * @throws NullPointerException if <code>in</code> is <code>null</code>
     */
    protected FilterReader(Reader in) {
        super(in);
        this.in = in;
    }

    /**
     * Reads a single character.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        return in.read();
    }

    /**
     * Reads characters into a portion of an array.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read(char cbuf[], int off, int len) throws IOException {
        return in.read(cbuf, off, len);
    }

    /**
     * Skips characters.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public long skip(long n) throws IOException {
        return in.skip(n);
    }

    /**
     * Tells whether this stream is ready to be read.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        return in.ready();
    }

    /**
     * Tells whether this stream supports the mark() operation.
     */
    public boolean markSupported() {
        return in.markSupported();
    }

    /**
     * Marks the present position in the stream.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        in.mark(readAheadLimit);
    }

    /**
     * Resets the stream.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void reset() throws IOException {
        in.reset();
    }

    public void close() throws IOException {
        in.close();
    }

}

⏎ java/io/FilterReader.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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