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/LayoutManager2.java

/*
 * Copyright (c) 1996, 2001, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.awt;

/**
 * Defines an interface for classes that know how to layout Containers
 * based on a layout constraints object.
 *
 * This interface extends the LayoutManager interface to deal with layouts
 * explicitly in terms of constraint objects that specify how and where
 * components should be added to the layout.
 * <p>
 * This minimal extension to LayoutManager is intended for tool
 * providers who wish to the creation of constraint-based layouts.
 * It does not yet provide full, general support for custom
 * constraint-based layout managers.
 *
 * @see LayoutManager
 * @see Container
 *
 * @author      Jonni Kanerva
 */
public interface LayoutManager2 extends LayoutManager {

    /**
     * Adds the specified component to the layout, using the specified
     * constraint object.
     * @param comp the component to be added
     * @param constraints  where/how the component is added to the layout.
     */
    void addLayoutComponent(Component comp, Object constraints);

    /**
     * Calculates the maximum size dimensions for the specified container,
     * given the components it contains.
     * @see java.awt.Component#getMaximumSize
     * @see LayoutManager
     */
    public Dimension maximumLayoutSize(Container target);

    /**
     * Returns the alignment along the x axis.  This specifies how
     * the component would like to be aligned relative to other
     * components.  The value should be a number between 0 and 1
     * where 0 represents alignment along the origin, 1 is aligned
     * the furthest away from the origin, 0.5 is centered, etc.
     */
    public float getLayoutAlignmentX(Container target);

    /**
     * Returns the alignment along the y axis.  This specifies how
     * the component would like to be aligned relative to other
     * components.  The value should be a number between 0 and 1
     * where 0 represents alignment along the origin, 1 is aligned
     * the furthest away from the origin, 0.5 is centered, etc.
     */
    public float getLayoutAlignmentY(Container target);

    /**
     * Invalidates the layout, indicating that if the layout manager
     * has cached information it should be discarded.
     */
    public void invalidateLayout(Container target);

}

⏎ java/awt/LayoutManager2.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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