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/awt/image/Kernel.java

/*
 * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.awt.image;


/**
 * The <code>Kernel</code> class defines a matrix that describes how a
 * specified pixel and its surrounding pixels affect the value
 * computed for the pixel's position in the output image of a filtering
 * operation.  The X origin and Y origin indicate the kernel matrix element
 * that corresponds to the pixel position for which an output value is
 * being computed.
 *
 * @see ConvolveOp
 */
public class Kernel implements Cloneable {
    private int  width;
    private int  height;
    private int  xOrigin;
    private int  yOrigin;
    private float data[];

    private static native void initIDs();
    static {
        ColorModel.loadLibraries();
        initIDs();
    }

    /**
     * Constructs a <code>Kernel</code> object from an array of floats.
     * The first <code>width</code>*<code>height</code> elements of
     * the <code>data</code> array are copied.
     * If the length of the <code>data</code> array is less
     * than width*height, an <code>IllegalArgumentException</code> is thrown.
     * The X origin is (width-1)/2 and the Y origin is (height-1)/2.
     * @param width         width of the kernel
     * @param height        height of the kernel
     * @param data          kernel data in row major order
     * @throws IllegalArgumentException if the length of <code>data</code>
     *         is less than the product of <code>width</code> and
     *         <code>height</code>
     */
    public Kernel(int width, int height, float data[]) {
        this.width  = width;
        this.height = height;
        this.xOrigin  = (width-1)>>1;
        this.yOrigin  = (height-1)>>1;
        int len = width*height;
        if (data.length < len) {
            throw new IllegalArgumentException("Data array too small "+
                                               "(is "+data.length+
                                               " and should be "+len);
        }
        this.data = new float[len];
        System.arraycopy(data, 0, this.data, 0, len);

    }

    /**
     * Returns the X origin of this <code>Kernel</code>.
     * @return the X origin.
     */
    final public int getXOrigin(){
        return xOrigin;
    }

    /**
     * Returns the Y origin of this <code>Kernel</code>.
     * @return the Y origin.
     */
    final public int getYOrigin() {
        return yOrigin;
    }

    /**
     * Returns the width of this <code>Kernel</code>.
     * @return the width of this <code>Kernel</code>.
     */
    final public int getWidth() {
        return width;
    }

    /**
     * Returns the height of this <code>Kernel</code>.
     * @return the height of this <code>Kernel</code>.
     */
    final public int getHeight() {
        return height;
    }

    /**
     * Returns the kernel data in row major order.
     * The <code>data</code> array is returned.  If <code>data</code>
     * is <code>null</code>, a new array is allocated.
     * @param data  if non-null, contains the returned kernel data
     * @return the <code>data</code> array containing the kernel data
     *         in row major order or, if <code>data</code> is
     *         <code>null</code>, a newly allocated array containing
     *         the kernel data in row major order
     * @throws IllegalArgumentException if <code>data</code> is less
     *         than the size of this <code>Kernel</code>
     */
    final public float[] getKernelData(float[] data) {
        if (data == null) {
            data = new float[this.data.length];
        }
        else if (data.length < this.data.length) {
            throw new IllegalArgumentException("Data array too small "+
                                               "(should be "+this.data.length+
                                               " but is "+
                                               data.length+" )");
        }
        System.arraycopy(this.data, 0, data, 0, this.data.length);

        return data;
    }

    /**
     * Clones this object.
     * @return a clone of this object.
     */
    public Object clone() {
        try {
            return super.clone();
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError(e);
        }
    }
}

⏎ java/awt/image/Kernel.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

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)