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/lang/Number.java

/*
 * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.lang;

/**
 * The abstract class {@code Number} is the superclass of platform
 * classes representing numeric values that are convertible to the
 * primitive types {@code byte}, {@code double}, {@code float}, {@code
 * int}, {@code long}, and {@code short}.
 *
 * The specific semantics of the conversion from the numeric value of
 * a particular {@code Number} implementation to a given primitive
 * type is defined by the {@code Number} implementation in question.
 *
 * For platform classes, the conversion is often analogous to a
 * narrowing primitive conversion or a widening primitive conversion
 * as defining in <cite>The Java&trade; Language Specification</cite>
 * for converting between primitive types.  Therefore, conversions may
 * lose information about the overall magnitude of a numeric value, may
 * lose precision, and may even return a result of a different sign
 * than the input.
 *
 * See the documentation of a given {@code Number} implementation for
 * conversion details.
 *
 * @author      Lee Boynton
 * @author      Arthur van Hoff
 * @jls 5.1.2 Widening Primitive Conversions
 * @jls 5.1.3 Narrowing Primitive Conversions
 * @since   JDK1.0
 */
public abstract class Number implements java.io.Serializable {
    /**
     * Returns the value of the specified number as an {@code int},
     * which may involve rounding or truncation.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code int}.
     */
    public abstract int intValue();

    /**
     * Returns the value of the specified number as a {@code long},
     * which may involve rounding or truncation.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code long}.
     */
    public abstract long longValue();

    /**
     * Returns the value of the specified number as a {@code float},
     * which may involve rounding.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code float}.
     */
    public abstract float floatValue();

    /**
     * Returns the value of the specified number as a {@code double},
     * which may involve rounding.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code double}.
     */
    public abstract double doubleValue();

    /**
     * Returns the value of the specified number as a {@code byte},
     * which may involve rounding or truncation.
     *
     * <p>This implementation returns the result of {@link #intValue} cast
     * to a {@code byte}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code byte}.
     * @since   JDK1.1
     */
    public byte byteValue() {
        return (byte)intValue();
    }

    /**
     * Returns the value of the specified number as a {@code short},
     * which may involve rounding or truncation.
     *
     * <p>This implementation returns the result of {@link #intValue} cast
     * to a {@code short}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code short}.
     * @since   JDK1.1
     */
    public short shortValue() {
        return (short)intValue();
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -8742448824652078965L;
}

⏎ java/lang/Number.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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