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/GridBagLayoutInfo.java

/*
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.awt;

/**
 * The {@code GridBagLayoutInfo} is an utility class for
 * {@code GridBagLayout} layout manager.
 * It stores align, size and baseline parameters for every component within a container.
 * <p>
 * @see       java.awt.GridBagLayout
 * @see       java.awt.GridBagConstraints
 * @since 1.6
 */
public class GridBagLayoutInfo implements java.io.Serializable {
    /*
     * serialVersionUID
     */
    private static final long serialVersionUID = -4899416460737170217L;

    int width, height;          /* number of  cells: horizontal and vertical */
    int startx, starty;         /* starting point for layout */
    int minWidth[];             /* largest minWidth in each column */
    int minHeight[];            /* largest minHeight in each row */
    double weightX[];           /* largest weight in each column */
    double weightY[];           /* largest weight in each row */
    boolean hasBaseline;        /* Whether or not baseline layout has been
                                 * requested and one of the components
                                 * has a valid baseline. */
    // These are only valid if hasBaseline is true and are indexed by
    // row.
    short baselineType[];       /* The type of baseline for a particular
                                 * row.  A mix of the BaselineResizeBehavior
                                 * constants (1 << ordinal()) */
    int maxAscent[];            /* Max ascent (baseline). */
    int maxDescent[];           /* Max descent (height - baseline) */

    /**
     * Creates an instance of GridBagLayoutInfo representing {@code GridBagLayout}
     * grid cells with it's own parameters.
     * @param width the columns
     * @param height the rows
     * @since 6.0
     */
    GridBagLayoutInfo(int width, int height) {
        this.width = width;
        this.height = height;
    }

    /**
     * Returns true if the specified row has any component aligned on the
     * baseline with a baseline resize behavior of CONSTANT_DESCENT.
     */
    boolean hasConstantDescent(int row) {
        return ((baselineType[row] & (1 << Component.BaselineResizeBehavior.
                                      CONSTANT_DESCENT.ordinal())) != 0);
    }

    /**
     * Returns true if there is a baseline for the specified row.
     */
    boolean hasBaseline(int row) {
        return (hasBaseline && baselineType[row] != 0);
    }
}

⏎ java/awt/GridBagLayoutInfo.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)