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/AssertionError.java

/*
 * Copyright (c) 2000, 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;

/**
 * Thrown to indicate that an assertion has failed.
 *
 * <p>The seven one-argument public constructors provided by this
 * class ensure that the assertion error returned by the invocation:
 * <pre>
 *     new AssertionError(<i>expression</i>)
 * </pre>
 * has as its detail message the <i>string conversion</i> of
 * <i>expression</i> (as defined in section 15.18.1.1 of
 * <cite>The Java&trade; Language Specification</cite>),
 * regardless of the type of <i>expression</i>.
 *
 * @since   1.4
 */
public class AssertionError extends Error {
    private static final long serialVersionUID = -5013299493970297370L;

    /**
     * Constructs an AssertionError with no detail message.
     */
    public AssertionError() {
    }

    /**
     * This internal constructor does no processing on its string argument,
     * even if it is a null reference.  The public constructors will
     * never call this constructor with a null argument.
     */
    private AssertionError(String detailMessage) {
        super(detailMessage);
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified object, which is converted to a string as
     * defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *<p>
     * If the specified object is an instance of {@code Throwable}, it
     * becomes the <i>cause</i> of the newly constructed assertion error.
     *
     * @param detailMessage value to be used in constructing detail message
     * @see   Throwable#getCause()
     */
    public AssertionError(Object detailMessage) {
        this(String.valueOf(detailMessage));
        if (detailMessage instanceof Throwable)
            initCause((Throwable) detailMessage);
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>boolean</code>, which is converted to
     * a string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(boolean detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>char</code>, which is converted to a
     * string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(char detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>int</code>, which is converted to a
     * string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(int detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>long</code>, which is converted to a
     * string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(long detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>float</code>, which is converted to a
     * string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(float detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs an AssertionError with its detail message derived
     * from the specified <code>double</code>, which is converted to a
     * string as defined in section 15.18.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param detailMessage value to be used in constructing detail message
     */
    public AssertionError(double detailMessage) {
        this(String.valueOf(detailMessage));
    }

    /**
     * Constructs a new {@code AssertionError} with the specified
     * detail message and cause.
     *
     * <p>Note that the detail message associated with
     * {@code cause} is <i>not</i> automatically incorporated in
     * this error's detail message.
     *
     * @param  message the detail message, may be {@code null}
     * @param  cause the cause, may be {@code null}
     *
     * @since 1.7
     */
    public AssertionError(String message, Throwable cause) {
        super(message, cause);
    }
}

⏎ java/lang/AssertionError.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
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