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	/*
	* Copyright (c) 2009, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.lang.module;

	import java.io.InputStream;
	import java.io.IOException;
	import java.io.PrintStream;
	import java.io.UncheckedIOException;
	import java.nio.ByteBuffer;
	import java.nio.file.Path;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.Collection;
	import java.util.Collections;
	import java.util.EnumSet;
	import java.util.HashMap;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Locale;
	import java.util.Map;
	import java.util.Objects;
	import java.util.Optional;
	import java.util.Set;
	import java.util.function.Supplier;
	import java.util.stream.Collectors;
	import java.util.stream.Stream;

	import static jdk.internal.module.Checks.*;
	import static java.util.Objects.*;

	import jdk.internal.module.Checks;
	import jdk.internal.module.ModuleInfo;


	/**
	* A module descriptor.
	*
	* <p> A module descriptor describes a named module and defines methods to
	* obtain each of its components. The module descriptor for a named module
	* in the Java virtual machine is obtained by invoking the {@link
	* java.lang.Module Module}'s {@link java.lang.Module#getDescriptor
	* getDescriptor} method. Module descriptors can also be created using the
	* {@link ModuleDescriptor.Builder} class or by reading the binary form of a
	* module declaration ({@code module-info.class}) using the {@link
	* #read(InputStream,Supplier) read} methods defined here. </p>
	*
	* <p> A module descriptor describes a <em>normal</em>, open, or automatic
	* module. <em>Normal</em> modules and open modules describe their {@linkplain
	* #requires() dependences}, {@link #exports() exported-packages}, the services
	* that they {@linkplain #uses() use} or {@linkplain #provides() provide}, and other
	* components. <em>Normal</em> modules may {@linkplain #opens() open} specific
	* packages. The module descriptor for an open module does not declare any
	* open packages (its {@code opens} method returns an empty set) but when
	* instantiated in the Java virtual machine then it is treated as if all
	* packages are open. The module descriptor for an automatic module does not
	* declare any dependences (except for the mandatory dependency on {@code
	* java.base}), and does not declare any exported or open packages. Automatic
	* modules receive special treatment during resolution so that they read all
	* other modules in the configuration. When an automatic module is instantiated
	* in the Java virtual machine then it reads every unnamed module and is
	* treated as if all packages are exported and open. </p>
	*
	* <p> {@code ModuleDescriptor} objects are immutable and safe for use by
	* multiple concurrent threads.</p>
	*
	* @see java.lang.Module
	* @since 9
	*/

	public class ModuleDescriptor
	implements Comparable<ModuleDescriptor>
	{

	/**
	* A modifier on a module.
	*
	* @see ModuleDescriptor#modifiers()
	* @since 9
	*/
	public enum Modifier {
	/**
	* An open module. An open module does not declare any open packages
	* but the resulting module is treated as if all packages are open.
	*/
	OPEN,

	/**
	* An automatic module. An automatic module is treated as if it exports
	* and opens all packages.
	*
	* @apiNote This modifier does not correspond to a module flag in the
	* binary form of a module declaration ({@code module-info.class}).
	*/
	AUTOMATIC,

	/**
	* The module was not explicitly or implicitly declared.
	*/
	SYNTHETIC,

	/**
	* The module was implicitly declared.
	*/
	MANDATED;
	}


	/**
	* <p> A dependence upon a module. </p>
	*
	* @see ModuleDescriptor#requires()
	* @since 9
	*/

	public static final class Requires
	implements Comparable<Requires>
	{

	/**
	* A modifier on a module dependence.
	*
	* @see Requires#modifiers()
	* @since 9
	*/
	public enum Modifier {

	/**
	* The dependence causes any module which depends on the <i>current
	* module</i> to have an implicitly declared dependence on the module
	* named by the {@code Requires}.
	*/
	TRANSITIVE,

	/**
	* The dependence is mandatory in the static phase, during compilation,
	* but is optional in the dynamic phase, during execution.
	*/
	STATIC,

	/**
	* The dependence was not explicitly or implicitly declared in the
	* source of the module declaration.
	*/
	SYNTHETIC,

	/**
	* The dependence was implicitly declared in the source of the module
	* declaration.
	*/
	MANDATED;

	}

	private final Set<Modifier> mods;
	private final String name;
	private final Version compiledVersion;
	private final String rawCompiledVersion;

	private Requires(Set<Modifier> ms, String mn, Version v, String vs) {
	assert v == null \|\| vs == null;
	this.mods = Set.copyOf(ms);
	this.name = mn;
	this.compiledVersion = v;
	this.rawCompiledVersion = vs;
	}

	private Requires(Set<Modifier> ms, String mn, Version v, boolean unused) {
	this.mods = ms;
	this.name = mn;
	this.compiledVersion = v;
	this.rawCompiledVersion = null;
	}

	/**
	* Returns the set of modifiers.
	*
	* @return A possibly-empty unmodifiable set of modifiers
	*/
	public Set<Modifier> modifiers() {
	return mods;
	}

	/**
	* Return the module name.
	*
	* @return The module name
	*/
	public String name() {
	return name;
	}

	/**
	* Returns the version of the module if recorded at compile-time.
	*
	* @return The version of the module if recorded at compile-time,
	* or an empty {@code Optional} if no version was recorded or
	* the version string recorded is {@linkplain Version#parse(String)
	* unparseable}
	*/
	public Optional<Version> compiledVersion() {
	return Optional.ofNullable(compiledVersion);
	}

	/**
	* Returns the string with the possibly-unparseable version of the module
	* if recorded at compile-time.
	*
	* @return The string containing the version of the module if recorded
	* at compile-time, or an empty {@code Optional} if no version
	* was recorded
	*
	* @see #compiledVersion()
	*/
	public Optional<String> rawCompiledVersion() {
	if (compiledVersion != null) {
	return Optional.of(compiledVersion.toString());
	} else {
	return Optional.ofNullable(rawCompiledVersion);
	}
	}

	/**
	* Compares this module dependence to another.
	*
	* <p> Two {@code Requires} objects are compared by comparing their
	* module names lexicographically. Where the module names are equal
	* then the sets of modifiers are compared in the same way that
	* module modifiers are compared (see {@link ModuleDescriptor#compareTo
	* ModuleDescriptor.compareTo}). Where the module names are equal and
	* the set of modifiers are equal then the version of the modules
	* recorded at compile-time are compared. When comparing the versions
	* recorded at compile-time then a dependence that has a recorded
	* version is considered to succeed a dependence that does not have a
	* recorded version. If both recorded versions are {@linkplain
	* Version#parse(String) unparseable} then the {@linkplain
	* #rawCompiledVersion() raw version strings} are compared
	* lexicographically. </p>
	*
	* @param that
	* The module dependence to compare
	*
	* @return A negative integer, zero, or a positive integer if this module
	* dependence is less than, equal to, or greater than the given
	* module dependence
	*/
	@Override
	public int compareTo(Requires that) {
	if (this == that) return 0;

	int c = this.name().compareTo(that.name());
	if (c != 0) return c;

	// modifiers
	long v1 = modsValue(this.modifiers());
	long v2 = modsValue(that.modifiers());
	c = Long.compare(v1, v2);
	if (c != 0) return c;

	// compiledVersion
	c = compare(this.compiledVersion, that.compiledVersion);
	if (c != 0) return c;

	// rawCompiledVersion
	c = compare(this.rawCompiledVersion, that.rawCompiledVersion);
	if (c != 0) return c;

	return 0;
	}

	/**
	* Tests this module dependence for equality with the given object.
	*
	* <p> If the given object is not a {@code Requires} then this method
	* returns {@code false}. Two module dependence objects are equal if
	* the module names are equal, set of modifiers are equal, and the
	* compiled version of both modules is equal or not recorded for
	* both modules. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a module
	* dependence that is equal to this module dependence
	*/
	@Override
	public boolean equals(Object ob) {
	return (ob instanceof Requires that)
	&& name.equals(that.name) && mods.equals(that.mods)
	&& Objects.equals(compiledVersion, that.compiledVersion)
	&& Objects.equals(rawCompiledVersion, that.rawCompiledVersion);
	}

	/**
	* Computes a hash code for this module dependence.
	*
	* <p> The hash code is based upon the module name, modifiers, and the
	* module version if recorded at compile time. It satisfies the general
	* contract of the {@link Object#hashCode Object.hashCode} method. </p>
	*
	* @return The hash-code value for this module dependence
	*/
	@Override
	public int hashCode() {
	int hash = name.hashCode() * 43 + mods.hashCode();
	if (compiledVersion != null)
	hash = hash * 43 + compiledVersion.hashCode();
	if (rawCompiledVersion != null)
	hash = hash * 43 + rawCompiledVersion.hashCode();
	return hash;
	}

	/**
	* Returns a string describing this module dependence.
	*
	* @return A string describing this module dependence
	*/
	@Override
	public String toString() {
	String what;
	if (compiledVersion != null) {
	what = name() + " (@" + compiledVersion + ")";
	} else {
	what = name();
	}
	return ModuleDescriptor.toString(mods, what);
	}
	}


	/**
	* <p> A package exported by a module, may be qualified or unqualified. </p>
	*
	* @see ModuleDescriptor#exports()
	* @since 9
	*/

	public static final class Exports
	implements Comparable<Exports>
	{

	/**
	* A modifier on an exported package.
	*
	* @see Exports#modifiers()
	* @since 9
	*/
	public enum Modifier {

	/**
	* The export was not explicitly or implicitly declared in the
	* source of the module declaration.
	*/
	SYNTHETIC,

	/**
	* The export was implicitly declared in the source of the module
	* declaration.
	*/
	MANDATED;

	}

	private final Set<Modifier> mods;
	private final String source;
	private final Set<String> targets; // empty if unqualified export

	/**
	* Constructs an export
	*/
	private Exports(Set<Modifier> ms, String source, Set<String> targets) {
	this.mods = Set.copyOf(ms);
	this.source = source;
	this.targets = Set.copyOf(targets);
	}

	private Exports(Set<Modifier> ms,
	String source,
	Set<String> targets,
	boolean unused) {
	this.mods = ms;
	this.source = source;
	this.targets = targets;
	}

	/**
	* Returns the set of modifiers.
	*
	* @return A possibly-empty unmodifiable set of modifiers
	*/
	public Set<Modifier> modifiers() {
	return mods;
	}

	/**
	* Returns {@code true} if this is a qualified export.
	*
	* @return {@code true} if this is a qualified export
	*/
	public boolean isQualified() {
	return !targets.isEmpty();
	}

	/**
	* Returns the package name.
	*
	* @return The package name
	*/
	public String source() {
	return source;
	}

	/**
	* For a qualified export, returns the non-empty and immutable set
	* of the module names to which the package is exported. For an
	* unqualified export, returns an empty set.
	*
	* @return The set of target module names or for an unqualified
	* export, an empty set
	*/
	public Set<String> targets() {
	return targets;
	}

	/**
	* Compares this module export to another.
	*
	* <p> Two {@code Exports} objects are compared by comparing the package
	* names lexicographically. Where the packages names are equal then the
	* sets of modifiers are compared in the same way that module modifiers
	* are compared (see {@link ModuleDescriptor#compareTo
	* ModuleDescriptor.compareTo}). Where the package names are equal and
	* the set of modifiers are equal then the set of target modules are
	* compared. This is done by sorting the names of the target modules
	* in ascending order, and according to their natural ordering, and then
	* comparing the corresponding elements lexicographically. Where the
	* sets differ in size, and the larger set contains all elements of the
	* smaller set, then the larger set is considered to succeed the smaller
	* set. </p>
	*
	* @param that
	* The module export to compare
	*
	* @return A negative integer, zero, or a positive integer if this module
	* export is less than, equal to, or greater than the given
	* export dependence
	*/
	@Override
	public int compareTo(Exports that) {
	if (this == that) return 0;

	int c = source.compareTo(that.source);
	if (c != 0)
	return c;

	// modifiers
	long v1 = modsValue(this.modifiers());
	long v2 = modsValue(that.modifiers());
	c = Long.compare(v1, v2);
	if (c != 0)
	return c;

	// targets
	c = compare(targets, that.targets);
	if (c != 0)
	return c;

	return 0;
	}

	/**
	* Computes a hash code for this module export.
	*
	* <p> The hash code is based upon the modifiers, the package name,
	* and for a qualified export, the set of modules names to which the
	* package is exported. It satisfies the general contract of the
	* {@link Object#hashCode Object.hashCode} method.
	*
	* @return The hash-code value for this module export
	*/
	@Override
	public int hashCode() {
	int hash = mods.hashCode();
	hash = hash * 43 + source.hashCode();
	return hash * 43 + targets.hashCode();
	}

	/**
	* Tests this module export for equality with the given object.
	*
	* <p> If the given object is not an {@code Exports} then this method
	* returns {@code false}. Two module exports objects are equal if their
	* set of modifiers is equal, the package names are equal and the set
	* of target module names is equal. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a module
	* dependence that is equal to this module dependence
	*/
	@Override
	public boolean equals(Object ob) {
	return (ob instanceof Exports other)
	&& Objects.equals(this.mods, other.mods)
	&& Objects.equals(this.source, other.source)
	&& Objects.equals(this.targets, other.targets);
	}

	/**
	* Returns a string describing the exported package.
	*
	* @return A string describing the exported package
	*/
	@Override
	public String toString() {
	String s = ModuleDescriptor.toString(mods, source);
	if (targets.isEmpty())
	return s;
	else
	return s + " to " + targets;
	}
	}


	/**
	* <p> A package opened by a module, may be qualified or unqualified. </p>
	*
	* <p> The <em>opens</em> directive in a module declaration declares a
	* package to be open to allow all types in the package, and all their
	* members, not just public types and their public members to be reflected
	* on by APIs that support private access or a way to bypass or suppress
	* default Java language access control checks. </p>
	*
	* @see ModuleDescriptor#opens()
	* @since 9
	*/

	public static final class Opens
	implements Comparable<Opens>
	{
	/**
	* A modifier on an open package.
	*
	* @see Opens#modifiers()
	* @since 9
	*/
	public enum Modifier {

	/**
	* The open package was not explicitly or implicitly declared in
	* the source of the module declaration.
	*/
	SYNTHETIC,

	/**
	* The open package was implicitly declared in the source of the
	* module declaration.
	*/
	MANDATED;

	}

	private final Set<Modifier> mods;
	private final String source;
	private final Set<String> targets; // empty if unqualified export

	/**
	* Constructs an {@code Opens}.
	*/
	private Opens(Set<Modifier> ms, String source, Set<String> targets) {
	this.mods = Set.copyOf(ms);
	this.source = source;
	this.targets = Set.copyOf(targets);
	}

	private Opens(Set<Modifier> ms,
	String source,
	Set<String> targets,
	boolean unused) {
	this.mods = ms;
	this.source = source;
	this.targets = targets;
	}

	/**
	* Returns the set of modifiers.
	*
	* @return A possibly-empty unmodifiable set of modifiers
	*/
	public Set<Modifier> modifiers() {
	return mods;
	}

	/**
	* Returns {@code true} if this is a qualified {@code Opens}.
	*
	* @return {@code true} if this is a qualified {@code Opens}
	*/
	public boolean isQualified() {
	return !targets.isEmpty();
	}

	/**
	* Returns the package name.
	*
	* @return The package name
	*/
	public String source() {
	return source;
	}

	/**
	* For a qualified {@code Opens}, returns the non-empty and immutable set
	* of the module names to which the package is open. For an
	* unqualified {@code Opens}, returns an empty set.
	*
	* @return The set of target module names or for an unqualified
	* {@code Opens}, an empty set
	*/
	public Set<String> targets() {
	return targets;
	}

	/**
	* Compares this module {@code Opens} to another.
	*
	* <p> Two {@code Opens} objects are compared by comparing the package
	* names lexicographically. Where the packages names are equal then the
	* sets of modifiers are compared in the same way that module modifiers
	* are compared (see {@link ModuleDescriptor#compareTo
	* ModuleDescriptor.compareTo}). Where the package names are equal and
	* the set of modifiers are equal then the set of target modules are
	* compared. This is done by sorting the names of the target modules
	* in ascending order, and according to their natural ordering, and then
	* comparing the corresponding elements lexicographically. Where the
	* sets differ in size, and the larger set contains all elements of the
	* smaller set, then the larger set is considered to succeed the smaller
	* set. </p>
	*
	* @param that
	* The module {@code Opens} to compare
	*
	* @return A negative integer, zero, or a positive integer if this module
	* {@code Opens} is less than, equal to, or greater than the given
	* module {@code Opens}
	*/
	@Override
	public int compareTo(Opens that) {
	if (this == that) return 0;

	int c = source.compareTo(that.source);
	if (c != 0)
	return c;

	// modifiers
	long v1 = modsValue(this.modifiers());
	long v2 = modsValue(that.modifiers());
	c = Long.compare(v1, v2);
	if (c != 0)
	return c;

	// targets
	c = compare(targets, that.targets);
	if (c != 0)
	return c;

	return 0;
	}

	/**
	* Computes a hash code for this module {@code Opens}.
	*
	* <p> The hash code is based upon the modifiers, the package name,
	* and for a qualified {@code Opens}, the set of modules names to which the
	* package is opened. It satisfies the general contract of the
	* {@link Object#hashCode Object.hashCode} method.
	*
	* @return The hash-code value for this module {@code Opens}
	*/
	@Override
	public int hashCode() {
	int hash = mods.hashCode();
	hash = hash * 43 + source.hashCode();
	return hash * 43 + targets.hashCode();
	}

	/**
	* Tests this module {@code Opens} for equality with the given object.
	*
	* <p> If the given object is not an {@code Opens} then this method
	* returns {@code false}. Two {@code Opens} objects are equal if their
	* set of modifiers is equal, the package names are equal and the set
	* of target module names is equal. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a module
	* dependence that is equal to this module dependence
	*/
	@Override
	public boolean equals(Object ob) {
	return (ob instanceof Opens other)
	&& Objects.equals(this.mods, other.mods)
	&& Objects.equals(this.source, other.source)
	&& Objects.equals(this.targets, other.targets);
	}

	/**
	* Returns a string describing the open package.
	*
	* @return A string describing the open package
	*/
	@Override
	public String toString() {
	String s = ModuleDescriptor.toString(mods, source);
	if (targets.isEmpty())
	return s;
	else
	return s + " to " + targets;
	}
	}


	/**
	* <p> A service that a module provides one or more implementations of. </p>
	*
	* @see ModuleDescriptor#provides()
	* @since 9
	*/

	public static final class Provides
	implements Comparable<Provides>
	{
	private final String service;
	private final List<String> providers;

	private Provides(String service, List<String> providers) {
	this.service = service;
	this.providers = List.copyOf(providers);
	}

	private Provides(String service, List<String> providers, boolean unused) {
	this.service = service;
	this.providers = providers;
	}

	/**
	* Returns the fully qualified class name of the service type.
	*
	* @return The fully qualified class name of the service type
	*/
	public String service() { return service; }

	/**
	* Returns the list of the fully qualified class names of the providers
	* or provider factories.
	*
	* @return A non-empty and unmodifiable list of the fully qualified class
	* names of the providers or provider factories
	*/
	public List<String> providers() { return providers; }

	/**
	* Compares this {@code Provides} to another.
	*
	* <p> Two {@code Provides} objects are compared by comparing the fully
	* qualified class name of the service type lexicographically. Where the
	* class names are equal then the list of the provider class names are
	* compared by comparing the corresponding elements of both lists
	* lexicographically and in sequence. Where the lists differ in size,
	* {@code N} is the size of the shorter list, and the first {@code N}
	* corresponding elements are equal, then the longer list is considered
	* to succeed the shorter list. </p>
	*
	* @param that
	* The {@code Provides} to compare
	*
	* @return A negative integer, zero, or a positive integer if this
	* {@code Provides} is less than, equal to, or greater than
	* the given {@code Provides}
	*/
	public int compareTo(Provides that) {
	if (this == that) return 0;

	int c = service.compareTo(that.service);
	if (c != 0) return c;

	// compare provider class names in sequence
	int size1 = this.providers.size();
	int size2 = that.providers.size();
	for (int index=0; index<Math.min(size1, size2); index++) {
	String e1 = this.providers.get(index);
	String e2 = that.providers.get(index);
	c = e1.compareTo(e2);
	if (c != 0) return c;
	}
	if (size1 == size2) {
	return 0;
	} else {
	return (size1 > size2) ? 1 : -1;
	}
	}

	/**
	* Computes a hash code for this {@code Provides}.
	*
	* <p> The hash code is based upon the service type and the set of
	* providers. It satisfies the general contract of the {@link
	* Object#hashCode Object.hashCode} method. </p>
	*
	* @return The hash-code value for this module provides
	*/
	@Override
	public int hashCode() {
	return service.hashCode() * 43 + providers.hashCode();
	}

	/**
	* Tests this {@code Provides} for equality with the given object.
	*
	* <p> If the given object is not a {@code Provides} then this method
	* returns {@code false}. Two {@code Provides} objects are equal if the
	* service type is equal and the list of providers is equal. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a
	* {@code Provides} that is equal to this {@code Provides}
	*/
	@Override
	public boolean equals(Object ob) {
	return (ob instanceof Provides other)
	&& Objects.equals(this.service, other.service)
	&& Objects.equals(this.providers, other.providers);
	}

	/**
	* Returns a string describing this {@code Provides}.
	*
	* @return A string describing this {@code Provides}
	*/
	@Override
	public String toString() {
	return service + " with " + providers;
	}

	}


	/**
	* A module's version string.
	*
	* <p> A version string has three components: The version number itself, an
	* optional pre-release version, and an optional build version. Each
	* component is a sequence of tokens; each token is either a non-negative
	* integer or a string. Tokens are separated by the punctuation characters
	* {@code '.'}, {@code '-'}, or {@code '+'}, or by transitions from a
	* sequence of digits to a sequence of characters that are neither digits
	* nor punctuation characters, or vice versa.
	*
	* <ul>
	*
	* <li> The <i>version number</i> is a sequence of tokens separated by
	* {@code '.'} characters, terminated by the first {@code '-'} or {@code
	* '+'} character. </li>
	*
	* <li> The <i>pre-release version</i> is a sequence of tokens separated
	* by {@code '.'} or {@code '-'} characters, terminated by the first
	* {@code '+'} character. </li>
	*
	* <li> The <i>build version</i> is a sequence of tokens separated by
	* {@code '.'}, {@code '-'}, or {@code '+'} characters.
	*
	* </ul>
	*
	* <p> When comparing two version strings, the elements of their
	* corresponding components are compared in pointwise fashion. If one
	* component is longer than the other, but otherwise equal to it, then the
	* first component is considered the greater of the two; otherwise, if two
	* corresponding elements are integers then they are compared as such;
	* otherwise, at least one of the elements is a string, so the other is
	* converted into a string if it is an integer and the two are compared
	* lexicographically. Trailing integer elements with the value zero are
	* ignored.
	*
	* <p> Given two version strings, if their version numbers differ then the
	* result of comparing them is the result of comparing their version
	* numbers; otherwise, if one of them has a pre-release version but the
	* other does not then the first is considered to precede the second,
	* otherwise the result of comparing them is the result of comparing their
	* pre-release versions; otherwise, the result of comparing them is the
	* result of comparing their build versions.
	*
	* @see ModuleDescriptor#version()
	* @since 9
	*/

	public static final class Version
	implements Comparable<Version>
	{

	private final String version;

	// If Java had disjunctive types then we'd write List<Integer\|String> here
	//
	private final List<Object> sequence;
	private final List<Object> pre;
	private final List<Object> build;

	// Take a numeric token starting at position i
	// Append it to the given list
	// Return the index of the first character not taken
	// Requires: s.charAt(i) is (decimal) numeric
	//
	private static int takeNumber(String s, int i, List<Object> acc) {
	char c = s.charAt(i);
	int d = (c - '0');
	int n = s.length();
	while (++i < n) {
	c = s.charAt(i);
	if (c >= '0' && c <= '9') {
	d = d * 10 + (c - '0');
	continue;
	}
	break;
	}
	acc.add(d);
	return i;
	}

	// Take a string token starting at position i
	// Append it to the given list
	// Return the index of the first character not taken
	// Requires: s.charAt(i) is not '.'
	//
	private static int takeString(String s, int i, List<Object> acc) {
	int b = i;
	int n = s.length();
	while (++i < n) {
	char c = s.charAt(i);
	if (c != '.' && c != '-' && c != '+' && !(c >= '0' && c <= '9'))
	continue;
	break;
	}
	acc.add(s.substring(b, i));
	return i;
	}

	// Syntax: tok+ ( '-' tok+)? ( '+' tok+)?
	// First token string is sequence, second is pre, third is build
	// Tokens are separated by '.' or '-', or by changes between alpha & numeric
	// Numeric tokens are compared as decimal integers
	// Non-numeric tokens are compared lexicographically
	// A version with a non-empty pre is less than a version with same seq but no pre
	// Tokens in build may contain '-' and '+'
	//
	private Version(String v) {

	if (v == null)
	throw new IllegalArgumentException("Null version string");
	int n = v.length();
	if (n == 0)
	throw new IllegalArgumentException("Empty version string");

	int i = 0;
	char c = v.charAt(i);
	if (!(c >= '0' && c <= '9'))
	throw new IllegalArgumentException(v
	+ ": Version string does not start"
	+ " with a number");

	List<Object> sequence = new ArrayList<>(4);
	List<Object> pre = new ArrayList<>(2);
	List<Object> build = new ArrayList<>(2);

	i = takeNumber(v, i, sequence);

	while (i < n) {
	c = v.charAt(i);
	if (c == '.') {
	i++;
	continue;
	}
	if (c == '-' \|\| c == '+') {
	i++;
	break;
	}
	if (c >= '0' && c <= '9')
	i = takeNumber(v, i, sequence);
	else
	i = takeString(v, i, sequence);
	}

	if (c == '-' && i >= n)
	throw new IllegalArgumentException(v + ": Empty pre-release");

	while (i < n) {
	c = v.charAt(i);
	if (c >= '0' && c <= '9')
	i = takeNumber(v, i, pre);
	else
	i = takeString(v, i, pre);
	if (i >= n)
	break;
	c = v.charAt(i);
	if (c == '.' \|\| c == '-') {
	i++;
	continue;
	}
	if (c == '+') {
	i++;
	break;
	}
	}

	if (c == '+' && i >= n)
	throw new IllegalArgumentException(v + ": Empty pre-release");

	while (i < n) {
	c = v.charAt(i);
	if (c >= '0' && c <= '9')
	i = takeNumber(v, i, build);
	else
	i = takeString(v, i, build);
	if (i >= n)
	break;
	c = v.charAt(i);
	if (c == '.' \|\| c == '-' \|\| c == '+') {
	i++;
	continue;
	}
	}

	this.version = v;
	this.sequence = sequence;
	this.pre = pre;
	this.build = build;
	}

	/**
	* Parses the given string as a version string.
	*
	* @param v
	* The string to parse
	*
	* @return The resulting {@code Version}
	*
	* @throws IllegalArgumentException
	* If {@code v} is {@code null}, an empty string, or cannot be
	* parsed as a version string
	*/
	public static Version parse(String v) {
	return new Version(v);
	}

	@SuppressWarnings("unchecked")
	private int cmp(Object o1, Object o2) {
	return ((Comparable)o1).compareTo(o2);
	}

	private int compareTokens(List<Object> ts1, List<Object> ts2) {
	int n = Math.min(ts1.size(), ts2.size());
	for (int i = 0; i < n; i++) {
	Object o1 = ts1.get(i);
	Object o2 = ts2.get(i);
	if ((o1 instanceof Integer && o2 instanceof Integer)
	\|\| (o1 instanceof String && o2 instanceof String))
	{
	int c = cmp(o1, o2);
	if (c == 0)
	continue;
	return c;
	}
	// Types differ, so convert number to string form
	int c = o1.toString().compareTo(o2.toString());
	if (c == 0)
	continue;
	return c;
	}
	List<Object> rest = ts1.size() > ts2.size() ? ts1 : ts2;
	int e = rest.size();
	for (int i = n; i < e; i++) {
	Object o = rest.get(i);
	if (o instanceof Integer && ((Integer)o) == 0)
	continue;
	return ts1.size() - ts2.size();
	}
	return 0;
	}

	/**
	* Compares this module version to another module version. Module
	* versions are compared as described in the class description.
	*
	* @param that
	* The module version to compare
	*
	* @return A negative integer, zero, or a positive integer as this
	* module version is less than, equal to, or greater than the
	* given module version
	*/
	@Override
	public int compareTo(Version that) {
	int c = compareTokens(this.sequence, that.sequence);
	if (c != 0) return c;
	if (this.pre.isEmpty()) {
	if (!that.pre.isEmpty()) return +1;
	} else {
	if (that.pre.isEmpty()) return -1;
	}
	c = compareTokens(this.pre, that.pre);
	if (c != 0) return c;
	return compareTokens(this.build, that.build);
	}

	/**
	* Tests this module version for equality with the given object.
	*
	* <p> If the given object is not a {@code Version} then this method
	* returns {@code false}. Two module version are equal if their
	* corresponding components are equal. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a module
	* reference that is equal to this module reference
	*/
	@Override
	public boolean equals(Object ob) {
	if (!(ob instanceof Version))
	return false;
	return compareTo((Version)ob) == 0;
	}

	/**
	* Computes a hash code for this module version.
	*
	* <p> The hash code is based upon the components of the version and
	* satisfies the general contract of the {@link Object#hashCode
	* Object.hashCode} method. </p>
	*
	* @return The hash-code value for this module version
	*/
	@Override
	public int hashCode() {
	return version.hashCode();
	}

	/**
	* Returns the string from which this version was parsed.
	*
	* @return The string from which this version was parsed.
	*/
	@Override
	public String toString() {
	return version;
	}

	}


	private final String name;
	private final Version version;
	private final String rawVersionString;
	private final Set<Modifier> modifiers;
	private final boolean open; // true if modifiers contains OPEN
	private final boolean automatic; // true if modifiers contains AUTOMATIC
	private final Set<Requires> requires;
	private final Set<Exports> exports;
	private final Set<Opens> opens;
	private final Set<String> uses;
	private final Set<Provides> provides;
	private final Set<String> packages;
	private final String mainClass;

	private ModuleDescriptor(String name,
	Version version,
	String rawVersionString,
	Set<Modifier> modifiers,
	Set<Requires> requires,
	Set<Exports> exports,
	Set<Opens> opens,
	Set<String> uses,
	Set<Provides> provides,
	Set<String> packages,
	String mainClass)
	{
	assert version == null \|\| rawVersionString == null;
	this.name = name;
	this.version = version;
	this.rawVersionString = rawVersionString;
	this.modifiers = Set.copyOf(modifiers);
	this.open = modifiers.contains(Modifier.OPEN);
	this.automatic = modifiers.contains(Modifier.AUTOMATIC);
	assert (requires.stream().map(Requires::name).distinct().count()
	== requires.size());
	this.requires = Set.copyOf(requires);
	this.exports = Set.copyOf(exports);
	this.opens = Set.copyOf(opens);
	this.uses = Set.copyOf(uses);
	this.provides = Set.copyOf(provides);

	this.packages = Set.copyOf(packages);
	this.mainClass = mainClass;
	}

	/**
	* Creates a module descriptor from its components.
	* The arguments are pre-validated and sets are unmodifiable sets.
	*/
	ModuleDescriptor(String name,
	Version version,
	Set<Modifier> modifiers,
	Set<Requires> requires,
	Set<Exports> exports,
	Set<Opens> opens,
	Set<String> uses,
	Set<Provides> provides,
	Set<String> packages,
	String mainClass,
	int hashCode,
	boolean unused) {
	this.name = name;
	this.version = version;
	this.rawVersionString = null;
	this.modifiers = modifiers;
	this.open = modifiers.contains(Modifier.OPEN);
	this.automatic = modifiers.contains(Modifier.AUTOMATIC);
	this.requires = requires;
	this.exports = exports;
	this.opens = opens;
	this.uses = uses;
	this.provides = provides;
	this.packages = packages;
	this.mainClass = mainClass;
	this.hash = hashCode;
	}

	/**
	* <p> Returns the module name. </p>
	*
	* @return The module name
	*/
	public String name() {
	return name;
	}

	/**
	* <p> Returns the set of module modifiers. </p>
	*
	* @return A possibly-empty unmodifiable set of modifiers
	*/
	public Set<Modifier> modifiers() {
	return modifiers;
	}

	/**
	* <p> Returns {@code true} if this is an open module. </p>
	*
	* <p> This method is equivalent to testing if the set of {@link #modifiers()
	* modifiers} contains the {@link Modifier#OPEN OPEN} modifier. </p>
	*
	* @return {@code true} if this is an open module
	*/
	public boolean isOpen() {
	return open;
	}

	/**
	* <p> Returns {@code true} if this is an automatic module. </p>
	*
	* <p> This method is equivalent to testing if the set of {@link #modifiers()
	* modifiers} contains the {@link Modifier#AUTOMATIC AUTOMATIC} modifier. </p>
	*
	* @return {@code true} if this is an automatic module
	*/
	public boolean isAutomatic() {
	return automatic;
	}

	/**
	* <p> Returns the set of {@code Requires} objects representing the module
	* dependences. </p>
	*
	* <p> The set includes a dependency on "{@code java.base}" when this
	* module is not named "{@code java.base}". If this module is an automatic
	* module then it does not have a dependency on any module other than
	* "{@code java.base}". </p>
	*
	* @return A possibly-empty unmodifiable set of {@link Requires} objects
	*/
	public Set<Requires> requires() {
	return requires;
	}

	/**
	* <p> Returns the set of {@code Exports} objects representing the exported
	* packages. </p>
	*
	* <p> If this module is an automatic module then the set of exports
	* is empty. </p>
	*
	* @return A possibly-empty unmodifiable set of exported packages
	*/
	public Set<Exports> exports() {
	return exports;
	}

	/**
	* <p> Returns the set of {@code Opens} objects representing the open
	* packages. </p>
	*
	* <p> If this module is an open module or an automatic module then the
	* set of open packages is empty. </p>
	*
	* @return A possibly-empty unmodifiable set of open packages
	*/
	public Set<Opens> opens() {
	return opens;
	}

	/**
	* <p> Returns the set of service dependences. </p>
	*
	* <p> If this module is an automatic module then the set of service
	* dependences is empty. </p>
	*
	* @return A possibly-empty unmodifiable set of the fully qualified class
	* names of the service types used
	*/
	public Set<String> uses() {
	return uses;
	}

	/**
	* <p> Returns the set of {@code Provides} objects representing the
	* services that the module provides. </p>
	*
	* @return The possibly-empty unmodifiable set of the services that this
	* module provides
	*/
	public Set<Provides> provides() {
	return provides;
	}

	/**
	* <p> Returns the module version. </p>
	*
	* @return This module's version, or an empty {@code Optional} if the
	* module does not have a version or the version is
	* {@linkplain Version#parse(String) unparseable}
	*/
	public Optional<Version> version() {
	return Optional.ofNullable(version);
	}

	/**
	* <p> Returns the string with the possibly-unparseable version of the
	* module. </p>
	*
	* @return The string containing the version of the module or an empty
	* {@code Optional} if the module does not have a version
	*
	* @see #version()
	*/
	public Optional<String> rawVersion() {
	if (version != null) {
	return Optional.of(version.toString());
	} else {
	return Optional.ofNullable(rawVersionString);
	}
	}

	/**
	* <p> Returns a string containing the module name and, if present, its
	* version. </p>
	*
	* @return A string containing the module name and, if present, its
	* version
	*/
	public String toNameAndVersion() {
	if (version != null) {
	return name() + "@" + version;
	} else {
	return name();
	}
	}

	/**
	* <p> Returns the module main class. </p>
	*
	* @return The fully qualified class name of the module's main class
	*/
	public Optional<String> mainClass() {
	return Optional.ofNullable(mainClass);
	}

	/**
	* Returns the set of packages in the module.
	*
	* <p> The set of packages includes all exported and open packages, as well
	* as the packages of any service providers, and the package for the main
	* class. </p>
	*
	* @return A possibly-empty unmodifiable set of the packages in the module
	*/
	public Set<String> packages() {
	return packages;
	}


	/**
	* A builder for building {@link ModuleDescriptor} objects.
	*
	* <p> {@code ModuleDescriptor} defines the {@link #newModule newModule},
	* {@link #newOpenModule newOpenModule}, and {@link #newAutomaticModule
	* newAutomaticModule} methods to create builders for building
	* <em>normal</em>, open, and automatic modules. </p>
	*
	* <p> The set of packages in the module are accumulated by the {@code
	* Builder} as the {@link ModuleDescriptor.Builder#exports(String) exports},
	* {@link ModuleDescriptor.Builder#opens(String) opens},
	* {@link ModuleDescriptor.Builder#packages(Set) packages},
	* {@link ModuleDescriptor.Builder#provides(String,List) provides}, and
	* {@link ModuleDescriptor.Builder#mainClass(String) mainClass} methods are
	* invoked. </p>
	*
	* <p> The module names, package names, and class names that are parameters
	* specified to the builder methods are the module names, package names,
	* and qualified names of classes (in named packages) as defined in the
	* <cite>The Java Language Specification</cite>. </p>
	*
	* <p> Example usage: </p>
	* <pre>{@code ModuleDescriptor descriptor = ModuleDescriptor.newModule("stats.core")
	* .requires("java.base")
	* .exports("org.acme.stats.core.clustering")
	* .exports("org.acme.stats.core.regression")
	* .packages(Set.of("org.acme.stats.core.internal"))
	* .build();
	* }</pre>
	*
	* @apiNote A {@code Builder} checks the components and invariants as
	* components are added to the builder. The rationale for this is to detect
	* errors as early as possible and not defer all validation to the
	* {@link #build build} method.
	*
	* @since 9
	*/
	public static final class Builder {
	final String name;
	final boolean strict;
	final Set<Modifier> modifiers;
	final boolean open;
	final boolean automatic;
	final Set<String> packages = new HashSet<>();
	final Map<String, Requires> requires = new HashMap<>();
	final Map<String, Exports> exports = new HashMap<>();
	final Map<String, Opens> opens = new HashMap<>();
	final Set<String> uses = new HashSet<>();
	final Map<String, Provides> provides = new HashMap<>();
	Version version;
	String rawVersionString;
	String mainClass;

	/**
	* Initializes a new builder with the given module name.
	*
	* If {@code strict} is {@code true} then module, package, and class
	* names are checked to ensure they are legal names. In addition, the
	* {@link #build buid} method will add "{@code requires java.base}" if
	* the dependency is not declared.
	*/
	Builder(String name, boolean strict, Set<Modifier> modifiers) {
	this.name = (strict) ? requireModuleName(name) : name;
	this.strict = strict;
	this.modifiers = modifiers;
	this.open = modifiers.contains(Modifier.OPEN);
	this.automatic = modifiers.contains(Modifier.AUTOMATIC);
	assert !open \|\| !automatic;
	}

	/**
	* Returns a snapshot of the packages in the module.
	*/
	/* package */ Set<String> packages() {
	return Collections.unmodifiableSet(packages);
	}

	/**
	* Adds a dependence on a module.
	*
	* @param req
	* The dependence
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the dependence is on the module that this builder was
	* initialized to build
	* @throws IllegalStateException
	* If the dependence on the module has already been declared
	* or this builder is for an automatic module
	*/
	public Builder requires(Requires req) {
	if (automatic)
	throw new IllegalStateException("Automatic modules cannot declare"
	+ " dependences");
	String mn = req.name();
	if (name.equals(mn))
	throw new IllegalArgumentException("Dependence on self");
	if (requires.containsKey(mn))
	throw new IllegalStateException("Dependence upon " + mn
	+ " already declared");
	requires.put(mn, req);
	return this;
	}

	/**
	* Adds a dependence on a module with the given (and possibly empty)
	* set of modifiers. The dependence includes the version of the
	* module that was recorded at compile-time.
	*
	* @param ms
	* The set of modifiers
	* @param mn
	* The module name
	* @param compiledVersion
	* The version of the module recorded at compile-time
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null}, is not a legal module
	* name, or is equal to the module name that this builder
	* was initialized to build
	* @throws IllegalStateException
	* If the dependence on the module has already been declared
	* or this builder is for an automatic module
	*/
	public Builder requires(Set<Requires.Modifier> ms,
	String mn,
	Version compiledVersion) {
	Objects.requireNonNull(compiledVersion);
	if (strict)
	mn = requireModuleName(mn);
	return requires(new Requires(ms, mn, compiledVersion, null));
	}

	/* package */Builder requires(Set<Requires.Modifier> ms,
	String mn,
	String rawCompiledVersion) {
	Requires r;
	try {
	Version v = Version.parse(rawCompiledVersion);
	r = new Requires(ms, mn, v, null);
	} catch (IllegalArgumentException e) {
	if (strict) throw e;
	r = new Requires(ms, mn, null, rawCompiledVersion);
	}
	return requires(r);
	}

	/**
	* Adds a dependence on a module with the given (and possibly empty)
	* set of modifiers.
	*
	* @param ms
	* The set of modifiers
	* @param mn
	* The module name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null}, is not a legal module
	* name, or is equal to the module name that this builder
	* was initialized to build
	* @throws IllegalStateException
	* If the dependence on the module has already been declared
	* or this builder is for an automatic module
	*/
	public Builder requires(Set<Requires.Modifier> ms, String mn) {
	if (strict)
	mn = requireModuleName(mn);
	return requires(new Requires(ms, mn, null, null));
	}

	/**
	* Adds a dependence on a module with an empty set of modifiers.
	*
	* @param mn
	* The module name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null}, is not a legal module
	* name, or is equal to the module name that this builder
	* was initialized to build
	* @throws IllegalStateException
	* If the dependence on the module has already been declared
	* or this builder is for an automatic module
	*/
	public Builder requires(String mn) {
	return requires(EnumSet.noneOf(Requires.Modifier.class), mn);
	}

	/**
	* Adds an exported package.
	*
	* @param e
	* The export
	*
	* @return This builder
	*
	* @throws IllegalStateException
	* If the {@link Exports#source() package} is already declared as
	* exported or this builder is for an automatic module
	*/
	public Builder exports(Exports e) {
	if (automatic) {
	throw new IllegalStateException("Automatic modules cannot declare"
	+ " exported packages");
	}
	String source = e.source();
	if (exports.containsKey(source)) {
	throw new IllegalStateException("Exported package " + source
	+ " already declared");
	}
	exports.put(source, e);
	packages.add(source);
	return this;
	}

	/**
	* Adds an exported package with the given (and possibly empty) set of
	* modifiers. The package is exported to a set of target modules.
	*
	* @param ms
	* The set of modifiers
	* @param pn
	* The package name
	* @param targets
	* The set of target modules names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name, the set of target modules is empty, or the set
	* of target modules contains a name that is not a legal module
	* name
	* @throws IllegalStateException
	* If the package is already declared as exported
	* or this builder is for an automatic module
	*/
	public Builder exports(Set<Exports.Modifier> ms,
	String pn,
	Set<String> targets)
	{
	targets = new HashSet<>(targets);
	if (targets.isEmpty())
	throw new IllegalArgumentException("Empty target set");
	if (strict) {
	requirePackageName(pn);
	targets.forEach(Checks::requireModuleName);
	}
	Exports e = new Exports(ms, pn, targets);
	return exports(e);
	}

	/**
	* Adds an exported package with the given (and possibly empty) set of
	* modifiers. The package is exported to all modules.
	*
	* @param ms
	* The set of modifiers
	* @param pn
	* The package name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name
	* @throws IllegalStateException
	* If the package is already declared as exported
	* or this builder is for an automatic module
	*/
	public Builder exports(Set<Exports.Modifier> ms, String pn) {
	if (strict) {
	requirePackageName(pn);
	}
	Exports e = new Exports(ms, pn, Set.of());
	return exports(e);
	}

	/**
	* Adds an exported package. The package is exported to a set of target
	* modules.
	*
	* @param pn
	* The package name
	* @param targets
	* The set of target modules names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name, the set of target modules is empty, or the set
	* of target modules contains a name that is not a legal module
	* name
	* @throws IllegalStateException
	* If the package is already declared as exported
	* or this builder is for an automatic module
	*/
	public Builder exports(String pn, Set<String> targets) {
	return exports(Set.of(), pn, targets);
	}

	/**
	* Adds an exported package. The package is exported to all modules.
	*
	* @param pn
	* The package name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name
	* @throws IllegalStateException
	* If the package is already declared as exported
	* or this builder is for an automatic module
	*/
	public Builder exports(String pn) {
	return exports(Set.of(), pn);
	}

	/**
	* Adds an open package.
	*
	* @param obj
	* The {@code Opens} object
	*
	* @return This builder
	*
	* @throws IllegalStateException
	* If the package is already declared as open, or this is a
	* builder for an open module or automatic module
	*/
	public Builder opens(Opens obj) {
	if (open \|\| automatic) {
	throw new IllegalStateException("Open or automatic modules cannot"
	+ " declare open packages");
	}
	String source = obj.source();
	if (opens.containsKey(source)) {
	throw new IllegalStateException("Open package " + source
	+ " already declared");
	}
	opens.put(source, obj);
	packages.add(source);
	return this;
	}


	/**
	* Adds an open package with the given (and possibly empty) set of
	* modifiers. The package is open to a set of target modules.
	*
	* @param ms
	* The set of modifiers
	* @param pn
	* The package name
	* @param targets
	* The set of target modules names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name, the set of target modules is empty, or the set
	* of target modules contains a name that is not a legal module
	* name
	* @throws IllegalStateException
	* If the package is already declared as open, or this is a
	* builder for an open module or automatic module
	*/
	public Builder opens(Set<Opens.Modifier> ms,
	String pn,
	Set<String> targets)
	{
	targets = new HashSet<>(targets);
	if (targets.isEmpty())
	throw new IllegalArgumentException("Empty target set");
	if (strict) {
	requirePackageName(pn);
	targets.forEach(Checks::requireModuleName);
	}
	Opens opens = new Opens(ms, pn, targets);
	return opens(opens);
	}

	/**
	* Adds an open package with the given (and possibly empty) set of
	* modifiers. The package is open to all modules.
	*
	* @param ms
	* The set of modifiers
	* @param pn
	* The package name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name
	* @throws IllegalStateException
	* If the package is already declared as open, or this is a
	* builder for an open module or automatic module
	*/
	public Builder opens(Set<Opens.Modifier> ms, String pn) {
	if (strict) {
	requirePackageName(pn);
	}
	Opens e = new Opens(ms, pn, Set.of());
	return opens(e);
	}

	/**
	* Adds an open package. The package is open to a set of target modules.
	*
	* @param pn
	* The package name
	* @param targets
	* The set of target modules names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name, the set of target modules is empty, or the set
	* of target modules contains a name that is not a legal module
	* name
	* @throws IllegalStateException
	* If the package is already declared as open, or this is a
	* builder for an open module or automatic module
	*/
	public Builder opens(String pn, Set<String> targets) {
	return opens(Set.of(), pn, targets);
	}

	/**
	* Adds an open package. The package is open to all modules.
	*
	* @param pn
	* The package name
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the package name is {@code null} or is not a legal
	* package name
	* @throws IllegalStateException
	* If the package is already declared as open, or this is a
	* builder for an open module or automatic module
	*/
	public Builder opens(String pn) {
	return opens(Set.of(), pn);
	}

	/**
	* Adds a service dependence.
	*
	* @param service
	* The service type
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the service type is {@code null} or not a qualified name of
	* a class in a named package
	* @throws IllegalStateException
	* If a dependency on the service type has already been declared
	* or this is a builder for an automatic module
	*/
	public Builder uses(String service) {
	if (automatic)
	throw new IllegalStateException("Automatic modules can not declare"
	+ " service dependences");
	if (uses.contains(requireServiceTypeName(service)))
	throw new IllegalStateException("Dependence upon service "
	+ service + " already declared");
	uses.add(service);
	return this;
	}

	/**
	* Provides a service with one or more implementations. The package for
	* each {@link Provides#providers provider} (or provider factory) is
	* added to the module if not already added.
	*
	* @param p
	* The provides
	*
	* @return This builder
	*
	* @throws IllegalStateException
	* If the providers for the service type have already been
	* declared
	*/
	public Builder provides(Provides p) {
	String service = p.service();
	if (provides.containsKey(service))
	throw new IllegalStateException("Providers of service "
	+ service + " already declared");
	provides.put(service, p);
	p.providers().forEach(name -> packages.add(packageName(name)));
	return this;
	}

	/**
	* Provides implementations of a service. The package for each provider
	* (or provider factory) is added to the module if not already added.
	*
	* @param service
	* The service type
	* @param providers
	* The list of provider or provider factory class names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If the service type or any of the provider class names is
	* {@code null} or not a qualified name of a class in a named
	* package, or the list of provider class names is empty
	* @throws IllegalStateException
	* If the providers for the service type have already been
	* declared
	*/
	public Builder provides(String service, List<String> providers) {
	providers = new ArrayList<>(providers);
	if (providers.isEmpty())
	throw new IllegalArgumentException("Empty providers set");
	if (strict) {
	requireServiceTypeName(service);
	providers.forEach(Checks::requireServiceProviderName);
	} else {
	// Disallow service/providers in unnamed package
	String pn = packageName(service);
	if (pn.isEmpty()) {
	throw new IllegalArgumentException(service
	+ ": unnamed package");
	}
	for (String name : providers) {
	pn = packageName(name);
	if (pn.isEmpty()) {
	throw new IllegalArgumentException(name
	+ ": unnamed package");
	}
	}
	}
	Provides p = new Provides(service, providers);
	return provides(p);
	}

	/**
	* Adds packages to the module. All packages in the set of package names
	* that are not in the module are added to module.
	*
	* @param pns
	* The (possibly empty) set of package names
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If any of the package names is {@code null} or is not a
	* legal package name
	*/
	public Builder packages(Set<String> pns) {
	if (strict) {
	pns = new HashSet<>(pns);
	pns.forEach(Checks::requirePackageName);
	}
	this.packages.addAll(pns);
	return this;
	}

	/**
	* Sets the module version.
	*
	* @param v
	* The version
	*
	* @return This builder
	*/
	public Builder version(Version v) {
	version = requireNonNull(v);
	rawVersionString = null;
	return this;
	}

	/**
	* Sets the module version.
	*
	* @param vs
	* The version string to parse
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If {@code vs} is {@code null} or cannot be parsed as a
	* version string
	*
	* @see Version#parse(String)
	*/
	public Builder version(String vs) {
	try {
	version = Version.parse(vs);
	rawVersionString = null;
	} catch (IllegalArgumentException e) {
	if (strict) throw e;
	version = null;
	rawVersionString = vs;
	}
	return this;
	}

	/**
	* Sets the module main class. The package for the main class is added
	* to the module if not already added. In other words, this method is
	* equivalent to first invoking this builder's {@link #packages(Set)
	* packages} method to add the package name of the main class.
	*
	* @param mc
	* The module main class
	*
	* @return This builder
	*
	* @throws IllegalArgumentException
	* If {@code mainClass} is {@code null} or not a qualified
	* name of a class in a named package
	*/
	public Builder mainClass(String mc) {
	String pn;
	if (strict) {
	mc = requireQualifiedClassName("main class name", mc);
	pn = packageName(mc);
	assert !pn.isEmpty();
	} else {
	// Disallow main class in unnamed package
	pn = packageName(mc);
	if (pn.isEmpty()) {
	throw new IllegalArgumentException(mc + ": unnamed package");
	}
	}
	packages.add(pn);
	mainClass = mc;
	return this;
	}

	/**
	* Builds and returns a {@code ModuleDescriptor} from its components.
	*
	* <p> The module will require "{@code java.base}" even if the dependence
	* has not been declared (the exception is when building a module named
	* "{@code java.base}" as it cannot require itself). The dependence on
	* "{@code java.base}" will have the {@link
	* java.lang.module.ModuleDescriptor.Requires.Modifier#MANDATED MANDATED}
	* modifier if the dependence was not declared. </p>
	*
	* @return The module descriptor
	*/
	public ModuleDescriptor build() {
	Set<Requires> requires = new HashSet<>(this.requires.values());
	Set<Exports> exports = new HashSet<>(this.exports.values());
	Set<Opens> opens = new HashSet<>(this.opens.values());

	// add dependency on java.base
	if (strict
	&& !name.equals("java.base")
	&& !this.requires.containsKey("java.base")) {
	requires.add(new Requires(Set.of(Requires.Modifier.MANDATED),
	"java.base",
	null,
	null));
	}

	Set<Provides> provides = new HashSet<>(this.provides.values());

	return new ModuleDescriptor(name,
	version,
	rawVersionString,
	modifiers,
	requires,
	exports,
	opens,
	uses,
	provides,
	packages,
	mainClass);
	}

	}

	/**
	* Compares this module descriptor to another.
	*
	* <p> Two {@code ModuleDescriptor} objects are compared by comparing their
	* module names lexicographically. Where the module names are equal then the
	* module versions are compared. When comparing the module versions then a
	* module descriptor with a version is considered to succeed a module
	* descriptor that does not have a version. If both versions are {@linkplain
	* Version#parse(String) unparseable} then the {@linkplain #rawVersion()
	* raw version strings} are compared lexicographically. Where the module names
	* are equal and the versions are equal (or not present in both), then the
	* set of modifiers are compared. Sets of modifiers are compared by comparing
	* a <em>binary value</em> computed for each set. If a modifier is present
	* in the set then the bit at the position of its ordinal is {@code 1}
	* in the binary value, otherwise {@code 0}. If the two set of modifiers
	* are also equal then the other components of the module descriptors are
	* compared in a manner that is consistent with {@code equals}. </p>
	*
	* @param that
	* The module descriptor to compare
	*
	* @return A negative integer, zero, or a positive integer if this module
	* descriptor is less than, equal to, or greater than the given
	* module descriptor
	*/
	@Override
	public int compareTo(ModuleDescriptor that) {
	if (this == that) return 0;

	int c = this.name().compareTo(that.name());
	if (c != 0) return c;

	c = compare(this.version, that.version);
	if (c != 0) return c;

	c = compare(this.rawVersionString, that.rawVersionString);
	if (c != 0) return c;

	long v1 = modsValue(this.modifiers());
	long v2 = modsValue(that.modifiers());
	c = Long.compare(v1, v2);
	if (c != 0) return c;

	c = compare(this.requires, that.requires);
	if (c != 0) return c;

	c = compare(this.packages, that.packages);
	if (c != 0) return c;

	c = compare(this.exports, that.exports);
	if (c != 0) return c;

	c = compare(this.opens, that.opens);
	if (c != 0) return c;

	c = compare(this.uses, that.uses);
	if (c != 0) return c;

	c = compare(this.provides, that.provides);
	if (c != 0) return c;

	c = compare(this.mainClass, that.mainClass);
	if (c != 0) return c;

	return 0;
	}

	/**
	* Tests this module descriptor for equality with the given object.
	*
	* <p> If the given object is not a {@code ModuleDescriptor} then this
	* method returns {@code false}. Two module descriptors are equal if each
	* of their corresponding components is equal. </p>
	*
	* <p> This method satisfies the general contract of the {@link
	* java.lang.Object#equals(Object) Object.equals} method. </p>
	*
	* @param ob
	* the object to which this object is to be compared
	*
	* @return {@code true} if, and only if, the given object is a module
	* descriptor that is equal to this module descriptor
	*/
	@Override
	public boolean equals(Object ob) {
	if (ob == this)
	return true;
	return (ob instanceof ModuleDescriptor that)
	&& (name.equals(that.name)
	&& modifiers.equals(that.modifiers)
	&& requires.equals(that.requires)
	&& Objects.equals(packages, that.packages)
	&& exports.equals(that.exports)
	&& opens.equals(that.opens)
	&& uses.equals(that.uses)
	&& provides.equals(that.provides)
	&& Objects.equals(version, that.version)
	&& Objects.equals(rawVersionString, that.rawVersionString)
	&& Objects.equals(mainClass, that.mainClass));
	}

	/**
	* Computes a hash code for this module descriptor.
	*
	* <p> The hash code is based upon the components of the module descriptor,
	* and satisfies the general contract of the {@link Object#hashCode
	* Object.hashCode} method. </p>
	*
	* @return The hash-code value for this module descriptor
	*/
	@Override
	public int hashCode() {
	int hc = hash;
	if (hc == 0) {
	hc = name.hashCode();
	hc = hc * 43 + Objects.hashCode(modifiers);
	hc = hc * 43 + requires.hashCode();
	hc = hc * 43 + Objects.hashCode(packages);
	hc = hc * 43 + exports.hashCode();
	hc = hc * 43 + opens.hashCode();
	hc = hc * 43 + uses.hashCode();
	hc = hc * 43 + provides.hashCode();
	hc = hc * 43 + Objects.hashCode(version);
	hc = hc * 43 + Objects.hashCode(rawVersionString);
	hc = hc * 43 + Objects.hashCode(mainClass);
	if (hc == 0)
	hc = -1;
	hash = hc;
	}
	return hc;
	}
	private transient int hash; // cached hash code

	/**
	* <p> Returns a string describing the module. </p>
	*
	* @return A string describing the module
	*/
	@Override
	public String toString() {
	StringBuilder sb = new StringBuilder();

	if (isOpen())
	sb.append("open ");
	sb.append("module { name: ").append(toNameAndVersion());
	if (!requires.isEmpty())
	sb.append(", ").append(requires);
	if (!uses.isEmpty())
	sb.append(", uses: ").append(uses);
	if (!exports.isEmpty())
	sb.append(", exports: ").append(exports);
	if (!opens.isEmpty())
	sb.append(", opens: ").append(opens);
	if (!provides.isEmpty()) {
	sb.append(", provides: ").append(provides);
	}
	sb.append(" }");
	return sb.toString();
	}


	/**
	* Instantiates a builder to build a module descriptor.
	*
	* @param name
	* The module name
	* @param ms
	* The set of module modifiers
	*
	* @return A new builder
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null} or is not a legal module
	* name, or the set of modifiers contains {@link
	* Modifier#AUTOMATIC AUTOMATIC} with other modifiers
	*/
	public static Builder newModule(String name, Set<Modifier> ms) {
	Set<Modifier> mods = new HashSet<>(ms);
	if (mods.contains(Modifier.AUTOMATIC) && mods.size() > 1)
	throw new IllegalArgumentException("AUTOMATIC cannot be used with"
	+ " other modifiers");

	return new Builder(name, true, mods);
	}

	/**
	* Instantiates a builder to build a module descriptor for a <em>normal</em>
	* module. This method is equivalent to invoking {@link #newModule(String,Set)
	* newModule} with an empty set of {@link ModuleDescriptor.Modifier modifiers}.
	*
	* @param name
	* The module name
	*
	* @return A new builder
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null} or is not a legal module
	* name
	*/
	public static Builder newModule(String name) {
	return new Builder(name, true, Set.of());
	}

	/**
	* Instantiates a builder to build a module descriptor for an open module.
	* This method is equivalent to invoking {@link #newModule(String,Set)
	* newModule} with the {@link ModuleDescriptor.Modifier#OPEN OPEN} modifier.
	*
	* <p> The builder for an open module cannot be used to declare any open
	* packages. </p>
	*
	* @param name
	* The module name
	*
	* @return A new builder that builds an open module
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null} or is not a legal module
	* name
	*/
	public static Builder newOpenModule(String name) {
	return new Builder(name, true, Set.of(Modifier.OPEN));
	}

	/**
	* Instantiates a builder to build a module descriptor for an automatic
	* module. This method is equivalent to invoking {@link #newModule(String,Set)
	* newModule} with the {@link ModuleDescriptor.Modifier#AUTOMATIC AUTOMATIC}
	* modifier.
	*
	* <p> The builder for an automatic module cannot be used to declare module
	* or service dependences. It also cannot be used to declare any exported
	* or open packages. </p>
	*
	* @param name
	* The module name
	*
	* @return A new builder that builds an automatic module
	*
	* @throws IllegalArgumentException
	* If the module name is {@code null} or is not a legal module
	* name
	*
	* @see ModuleFinder#of(Path[])
	*/
	public static Builder newAutomaticModule(String name) {
	return new Builder(name, true, Set.of(Modifier.AUTOMATIC));
	}


	/**
	* Reads the binary form of a module declaration from an input stream
	* as a module descriptor.
	*
	* <p> If the descriptor encoded in the input stream does not indicate a
	* set of packages in the module then the {@code packageFinder} will be
	* invoked. The set of packages that the {@code packageFinder} returns
	* must include all the packages that the module exports, opens, as well
	* as the packages of the service implementations that the module provides,
	* and the package of the main class (if the module has a main class). If
	* the {@code packageFinder} throws an {@link UncheckedIOException} then
	* {@link IOException} cause will be re-thrown. </p>
	*
	* <p> If there are bytes following the module descriptor then it is
	* implementation specific as to whether those bytes are read, ignored,
	* or reported as an {@code InvalidModuleDescriptorException}. If this
	* method fails with an {@code InvalidModuleDescriptorException} or {@code
	* IOException} then it may do so after some, but not all, bytes have
	* been read from the input stream. It is strongly recommended that the
	* stream be promptly closed and discarded if an exception occurs. </p>
	*
	* @apiNote The {@code packageFinder} parameter is for use when reading
	* module descriptors from legacy module-artifact formats that do not
	* record the set of packages in the descriptor itself.
	*
	* @param in
	* The input stream
	* @param packageFinder
	* A supplier that can produce the set of packages
	*
	* @return The module descriptor
	*
	* @throws InvalidModuleDescriptorException
	* If an invalid module descriptor is detected or the set of
	* packages returned by the {@code packageFinder} does not include
	* all of the packages obtained from the module descriptor
	* @throws IOException
	* If an I/O error occurs reading from the input stream or {@code
	* UncheckedIOException} is thrown by the package finder
	*/
	public static ModuleDescriptor read(InputStream in,
	Supplier<Set<String>> packageFinder)
	throws IOException
	{
	return ModuleInfo.read(in, requireNonNull(packageFinder)).descriptor();
	}

	/**
	* Reads the binary form of a module declaration from an input stream as a
	* module descriptor. This method works exactly as specified by the 2-arg
	* {@link #read(InputStream,Supplier) read} method with the exception that
	* a packager finder is not used to find additional packages when the
	* module descriptor read from the stream does not indicate the set of
	* packages.
	*
	* @param in
	* The input stream
	*
	* @return The module descriptor
	*
	* @throws InvalidModuleDescriptorException
	* If an invalid module descriptor is detected
	* @throws IOException
	* If an I/O error occurs reading from the input stream
	*/
	public static ModuleDescriptor read(InputStream in) throws IOException {
	return ModuleInfo.read(in, null).descriptor();
	}

	/**
	* Reads the binary form of a module declaration from a byte buffer
	* as a module descriptor.
	*
	* <p> If the descriptor encoded in the byte buffer does not indicate a
	* set of packages in the module then the {@code packageFinder} will be
	* invoked. The set of packages that the {@code packageFinder} returns
	* must include all the packages that the module exports, opens, as well
	* as the packages of the service implementations that the module provides,
	* and the package of the main class (if the module has a main class). If
	* the {@code packageFinder} throws an {@link UncheckedIOException} then
	* {@link IOException} cause will be re-thrown. </p>
	*
	* <p> The module descriptor is read from the buffer starting at index
	* {@code p}, where {@code p} is the buffer's {@link ByteBuffer#position()
	* position} when this method is invoked. Upon return the buffer's position
	* will be equal to {@code p + n} where {@code n} is the number of bytes
	* read from the buffer. </p>
	*
	* <p> If there are bytes following the module descriptor then it is
	* implementation specific as to whether those bytes are read, ignored,
	* or reported as an {@code InvalidModuleDescriptorException}. If this
	* method fails with an {@code InvalidModuleDescriptorException} then it
	* may do so after some, but not all, bytes have been read. </p>
	*
	* @apiNote The {@code packageFinder} parameter is for use when reading
	* module descriptors from legacy module-artifact formats that do not
	* record the set of packages in the descriptor itself.
	*
	* @param bb
	* The byte buffer
	* @param packageFinder
	* A supplier that can produce the set of packages
	*
	* @return The module descriptor
	*
	* @throws InvalidModuleDescriptorException
	* If an invalid module descriptor is detected or the set of
	* packages returned by the {@code packageFinder} does not include
	* all of the packages obtained from the module descriptor
	*/
	public static ModuleDescriptor read(ByteBuffer bb,
	Supplier<Set<String>> packageFinder)
	{
	return ModuleInfo.read(bb, requireNonNull(packageFinder)).descriptor();
	}

	/**
	* Reads the binary form of a module declaration from a byte buffer as a
	* module descriptor. This method works exactly as specified by the 2-arg
	* {@link #read(ByteBuffer,Supplier) read} method with the exception that a
	* packager finder is not used to find additional packages when the module
	* descriptor encoded in the buffer does not indicate the set of packages.
	*
	* @param bb
	* The byte buffer
	*
	* @return The module descriptor
	*
	* @throws InvalidModuleDescriptorException
	* If an invalid module descriptor is detected
	*/
	public static ModuleDescriptor read(ByteBuffer bb) {
	return ModuleInfo.read(bb, null).descriptor();
	}

	private static String packageName(String cn) {
	int index = cn.lastIndexOf('.');
	return (index == -1) ? "" : cn.substring(0, index);
	}

	/**
	* Returns a string containing the given set of modifiers and label.
	*/
	private static <M> String toString(Set<M> mods, String what) {
	return (Stream.concat(mods.stream().map(e -> e.toString()
	.toLowerCase(Locale.ROOT)),
	Stream.of(what)))
	.collect(Collectors.joining(" "));
	}

	private static <T extends Object & Comparable<? super T>>
	int compare(T obj1, T obj2) {
	if (obj1 != null) {
	return (obj2 != null) ? obj1.compareTo(obj2) : 1;
	} else {
	return (obj2 == null) ? 0 : -1;
	}
	}

	/**
	* Compares two sets of {@code Comparable} objects.
	*/
	@SuppressWarnings("unchecked")
	private static <T extends Object & Comparable<? super T>>
	int compare(Set<T> s1, Set<T> s2) {
	T[] a1 = (T[]) s1.toArray();
	T[] a2 = (T[]) s2.toArray();
	Arrays.sort(a1);
	Arrays.sort(a2);
	return Arrays.compare(a1, a2);
	}

	private static <E extends Enum<E>> long modsValue(Set<E> set) {
	long value = 0;
	for (Enum<E> e : set) {
	value += 1 << e.ordinal();
	}
	return value;
	}

	static {
	/**
	* Setup the shared secret to allow code in other packages access
	* private package methods in java.lang.module.
	*/
	jdk.internal.access.SharedSecrets
	.setJavaLangModuleAccess(new jdk.internal.access.JavaLangModuleAccess() {
	@Override
	public Builder newModuleBuilder(String mn,
	boolean strict,
	Set<ModuleDescriptor.Modifier> modifiers) {
	return new Builder(mn, strict, modifiers);
	}

	@Override
	public Set<String> packages(ModuleDescriptor.Builder builder) {
	return builder.packages();
	}

	@Override
	public void requires(ModuleDescriptor.Builder builder,
	Set<Requires.Modifier> ms,
	String mn,
	String rawCompiledVersion) {
	builder.requires(ms, mn, rawCompiledVersion);
	}

	@Override
	public Requires newRequires(Set<Requires.Modifier> ms, String mn, Version v) {
	return new Requires(ms, mn, v, true);
	}

	@Override
	public Exports newExports(Set<Exports.Modifier> ms, String source) {
	return new Exports(ms, source, Set.of(), true);
	}

	@Override
	public Exports newExports(Set<Exports.Modifier> ms,
	String source,
	Set<String> targets) {
	return new Exports(ms, source, targets, true);
	}

	@Override
	public Opens newOpens(Set<Opens.Modifier> ms,
	String source,
	Set<String> targets) {
	return new Opens(ms, source, targets, true);
	}

	@Override
	public Opens newOpens(Set<Opens.Modifier> ms, String source) {
	return new Opens(ms, source, Set.of(), true);
	}

	@Override
	public Provides newProvides(String service, List<String> providers) {
	return new Provides(service, providers, true);
	}

	@Override
	public ModuleDescriptor newModuleDescriptor(String name,
	Version version,
	Set<ModuleDescriptor.Modifier> modifiers,
	Set<Requires> requires,
	Set<Exports> exports,
	Set<Opens> opens,
	Set<String> uses,
	Set<Provides> provides,
	Set<String> packages,
	String mainClass,
	int hashCode) {
	return new ModuleDescriptor(name,
	version,
	modifiers,
	requires,
	exports,
	opens,
	uses,
	provides,
	packages,
	mainClass,
	hashCode,
	false);
	}

	@Override
	public Configuration resolveAndBind(ModuleFinder finder,
	Collection<String> roots,
	PrintStream traceOutput)
	{
	return Configuration.resolveAndBind(finder, roots, traceOutput);
	}

	@Override
	public Configuration newConfiguration(ModuleFinder finder,
	Map<String, Set<String>> graph) {
	return new Configuration(finder, graph);
	}
	});
	}

	}

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