/*
* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
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*
*
*
*
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*
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*
*
*
*/
package javax.imageio.spi;
import java.io.
File;
import java.security.
AccessControlContext;
import java.security.
AccessController;
import java.security.
PrivilegedAction;
import java.util.
ArrayList;
import java.util.
HashMap;
import java.util.
Iterator;
import java.util.
List;
import java.util.
Map;
import java.util.
NoSuchElementException;
import java.util.
Set;
import java.util.
ServiceLoader;
/**
* A registry for service provider instances.
*
* <p> A <i>service</i> is a well-known set of interfaces and (usually
* abstract) classes. A <i>service provider</i> is a specific
* implementation of a service. The classes in a provider typically
* implement the interface or subclass the class defined by the
* service itself.
*
* <p> Service providers are stored in one or more <i>categories</i>,
* each of which is defined by a class of interface (described by a
* <code>Class</code> object) that all of its members must implement.
* The set of categories may be changed dynamically.
*
* <p> Only a single instance of a given leaf class (that is, the
* actual class returned by <code>getClass()</code>, as opposed to any
* inherited classes or interfaces) may be registered. That is,
* suppose that the
* <code>com.mycompany.mypkg.GreenServiceProvider</code> class
* implements the <code>com.mycompany.mypkg.MyService</code>
* interface. If a <code>GreenServiceProvider</code> instance is
* registered, it will be stored in the category defined by the
* <code>MyService</code> class. If a new instance of
* <code>GreenServiceProvider</code> is registered, it will replace
* the previous instance. In practice, service provider objects are
* usually singletons so this behavior is appropriate.
*
* <p> To declare a service provider, a <code>services</code>
* subdirectory is placed within the <code>META-INF</code> directory
* that is present in every JAR file. This directory contains a file
* for each service provider interface that has one or more
* implementation classes present in the JAR file. For example, if
* the JAR file contained a class named
* <code>com.mycompany.mypkg.MyServiceImpl</code> which implements the
* <code>javax.someapi.SomeService</code> interface, the JAR file
* would contain a file named: <pre>
* META-INF/services/javax.someapi.SomeService </pre>
*
* containing the line:
*
* <pre>
* com.mycompany.mypkg.MyService
* </pre>
*
* <p> The service provider classes should be to be lightweight and
* quick to load. Implementations of these interfaces should avoid
* complex dependencies on other classes and on native code. The usual
* pattern for more complex services is to register a lightweight
* proxy for the heavyweight service.
*
* <p> An application may customize the contents of a registry as it
* sees fit, so long as it has the appropriate runtime permission.
*
* <p> For more details on declaring service providers, and the JAR
* format in general, see the <a
* href="../../../../technotes/guides/jar/jar.html">
* JAR File Specification</a>.
*
* @see RegisterableService
*
*/
public class
ServiceRegistry {
// Class -> Registry
private
Map categoryMap = new
HashMap();
/**
* Constructs a <code>ServiceRegistry</code> instance with a
* set of categories taken from the <code>categories</code>
* argument.
*
* @param categories an <code>Iterator</code> containing
* <code>Class</code> objects to be used to define categories.
*
* @exception IllegalArgumentException if
* <code>categories</code> is <code>null</code>.
*/
public
ServiceRegistry(
Iterator<
Class<?>>
categories) {
if (
categories == null) {
throw new
IllegalArgumentException("categories == null!");
}
while (
categories.
hasNext()) {
Class category = (
Class)
categories.
next();
SubRegistry reg = new
SubRegistry(this,
category);
categoryMap.
put(
category,
reg);
}
}
// The following two methods expose functionality from
// sun.misc.Service. If that class is made public, they may be
// removed.
//
// The sun.misc.ServiceConfigurationError class may also be
// exposed, in which case the references to 'an
// <code>Error</code>' below should be changed to 'a
// <code>ServiceConfigurationError</code>'.
/**
* Searches for implementations of a particular service class
* using the given class loader.
*
* <p> This method transforms the name of the given service class
* into a provider-configuration filename as described in the
* class comment and then uses the <code>getResources</code>
* method of the given class loader to find all available files
* with that name. These files are then read and parsed to
* produce a list of provider-class names. The iterator that is
* returned uses the given class loader to look up and then
* instantiate each element of the list.
*
* <p> Because it is possible for extensions to be installed into
* a running Java virtual machine, this method may return
* different results each time it is invoked.
*
* @param providerClass a <code>Class</code>object indicating the
* class or interface of the service providers being detected.
*
* @param loader the class loader to be used to load
* provider-configuration files and instantiate provider classes,
* or <code>null</code> if the system class loader (or, failing that
* the bootstrap class loader) is to be used.
*
* @param <T> the type of the providerClass.
*
* @return An <code>Iterator</code> that yields provider objects
* for the given service, in some arbitrary order. The iterator
* will throw an <code>Error</code> if a provider-configuration
* file violates the specified format or if a provider class
* cannot be found and instantiated.
*
* @exception IllegalArgumentException if
* <code>providerClass</code> is <code>null</code>.
*/
public static <T>
Iterator<T>
lookupProviders(
Class<T>
providerClass,
ClassLoader loader)
{
if (
providerClass == null) {
throw new
IllegalArgumentException("providerClass == null!");
}
return
ServiceLoader.
load(
providerClass,
loader).
iterator();
}
/**
* Locates and incrementally instantiates the available providers
* of a given service using the context class loader. This
* convenience method is equivalent to:
*
* <pre>
* ClassLoader cl = Thread.currentThread().getContextClassLoader();
* return Service.providers(service, cl);
* </pre>
*
* @param providerClass a <code>Class</code>object indicating the
* class or interface of the service providers being detected.
*
* @param <T> the type of the providerClass.
*
* @return An <code>Iterator</code> that yields provider objects
* for the given service, in some arbitrary order. The iterator
* will throw an <code>Error</code> if a provider-configuration
* file violates the specified format or if a provider class
* cannot be found and instantiated.
*
* @exception IllegalArgumentException if
* <code>providerClass</code> is <code>null</code>.
*/
public static <T>
Iterator<T>
lookupProviders(
Class<T>
providerClass) {
if (
providerClass == null) {
throw new
IllegalArgumentException("providerClass == null!");
}
return
ServiceLoader.
load(
providerClass).
iterator();
}
/**
* Returns an <code>Iterator</code> of <code>Class</code> objects
* indicating the current set of categories. The iterator will be
* empty if no categories exist.
*
* @return an <code>Iterator</code> containing
* <code>Class</code>objects.
*/
public
Iterator<
Class<?>>
getCategories() {
Set keySet =
categoryMap.
keySet();
return
keySet.
iterator();
}
/**
* Returns an Iterator containing the subregistries to which the
* provider belongs.
*/
private
Iterator getSubRegistries(
Object provider) {
List l = new
ArrayList();
Iterator iter =
categoryMap.
keySet().
iterator();
while (
iter.
hasNext()) {
Class c = (
Class)
iter.
next();
if (
c.
isAssignableFrom(
provider.
getClass())) {
l.
add((
SubRegistry)
categoryMap.
get(
c));
}
}
return
l.
iterator();
}
/**
* Adds a service provider object to the registry. The provider
* is associated with the given category.
*
* <p> If <code>provider</code> implements the
* <code>RegisterableService</code> interface, its
* <code>onRegistration</code> method will be called. Its
* <code>onDeregistration</code> method will be called each time
* it is deregistered from a category, for example if a
* category is removed or the registry is garbage collected.
*
* @param provider the service provide object to be registered.
* @param category the category under which to register the
* provider.
* @param <T> the type of the provider.
*
* @return true if no provider of the same class was previously
* registered in the same category category.
*
* @exception IllegalArgumentException if <code>provider</code> is
* <code>null</code>.
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
* @exception ClassCastException if provider does not implement
* the <code>Class</code> defined by <code>category</code>.
*/
public <T> boolean
registerServiceProvider(T
provider,
Class<T>
category) {
if (
provider == null) {
throw new
IllegalArgumentException("provider == null!");
}
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
if (!
category.
isAssignableFrom(
provider.
getClass())) {
throw new
ClassCastException();
}
return
reg.
registerServiceProvider(
provider);
}
/**
* Adds a service provider object to the registry. The provider
* is associated within each category present in the registry
* whose <code>Class</code> it implements.
*
* <p> If <code>provider</code> implements the
* <code>RegisterableService</code> interface, its
* <code>onRegistration</code> method will be called once for each
* category it is registered under. Its
* <code>onDeregistration</code> method will be called each time
* it is deregistered from a category or when the registry is
* finalized.
*
* @param provider the service provider object to be registered.
*
* @exception IllegalArgumentException if
* <code>provider</code> is <code>null</code>.
*/
public void
registerServiceProvider(
Object provider) {
if (
provider == null) {
throw new
IllegalArgumentException("provider == null!");
}
Iterator regs =
getSubRegistries(
provider);
while (
regs.
hasNext()) {
SubRegistry reg = (
SubRegistry)
regs.
next();
reg.
registerServiceProvider(
provider);
}
}
/**
* Adds a set of service provider objects, taken from an
* <code>Iterator</code> to the registry. Each provider is
* associated within each category present in the registry whose
* <code>Class</code> it implements.
*
* <p> For each entry of <code>providers</code> that implements
* the <code>RegisterableService</code> interface, its
* <code>onRegistration</code> method will be called once for each
* category it is registered under. Its
* <code>onDeregistration</code> method will be called each time
* it is deregistered from a category or when the registry is
* finalized.
*
* @param providers an Iterator containing service provider
* objects to be registered.
*
* @exception IllegalArgumentException if <code>providers</code>
* is <code>null</code> or contains a <code>null</code> entry.
*/
public void
registerServiceProviders(
Iterator<?>
providers) {
if (
providers == null) {
throw new
IllegalArgumentException("provider == null!");
}
while (
providers.
hasNext()) {
registerServiceProvider(
providers.
next());
}
}
/**
* Removes a service provider object from the given category. If
* the provider was not previously registered, nothing happens and
* <code>false</code> is returned. Otherwise, <code>true</code>
* is returned. If an object of the same class as
* <code>provider</code> but not equal (using <code>==</code>) to
* <code>provider</code> is registered, it will not be
* deregistered.
*
* <p> If <code>provider</code> implements the
* <code>RegisterableService</code> interface, its
* <code>onDeregistration</code> method will be called.
*
* @param provider the service provider object to be deregistered.
* @param category the category from which to deregister the
* provider.
* @param <T> the type of the provider.
*
* @return <code>true</code> if the provider was previously
* registered in the same category category,
* <code>false</code> otherwise.
*
* @exception IllegalArgumentException if <code>provider</code> is
* <code>null</code>.
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
* @exception ClassCastException if provider does not implement
* the class defined by <code>category</code>.
*/
public <T> boolean
deregisterServiceProvider(T
provider,
Class<T>
category) {
if (
provider == null) {
throw new
IllegalArgumentException("provider == null!");
}
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
if (!
category.
isAssignableFrom(
provider.
getClass())) {
throw new
ClassCastException();
}
return
reg.
deregisterServiceProvider(
provider);
}
/**
* Removes a service provider object from all categories that
* contain it.
*
* @param provider the service provider object to be deregistered.
*
* @exception IllegalArgumentException if <code>provider</code> is
* <code>null</code>.
*/
public void
deregisterServiceProvider(
Object provider) {
if (
provider == null) {
throw new
IllegalArgumentException("provider == null!");
}
Iterator regs =
getSubRegistries(
provider);
while (
regs.
hasNext()) {
SubRegistry reg = (
SubRegistry)
regs.
next();
reg.
deregisterServiceProvider(
provider);
}
}
/**
* Returns <code>true</code> if <code>provider</code> is currently
* registered.
*
* @param provider the service provider object to be queried.
*
* @return <code>true</code> if the given provider has been
* registered.
*
* @exception IllegalArgumentException if <code>provider</code> is
* <code>null</code>.
*/
public boolean
contains(
Object provider) {
if (
provider == null) {
throw new
IllegalArgumentException("provider == null!");
}
Iterator regs =
getSubRegistries(
provider);
while (
regs.
hasNext()) {
SubRegistry reg = (
SubRegistry)
regs.
next();
if (
reg.
contains(
provider)) {
return true;
}
}
return false;
}
/**
* Returns an <code>Iterator</code> containing all registered
* service providers in the given category. If
* <code>useOrdering</code> is <code>false</code>, the iterator
* will return all of the server provider objects in an arbitrary
* order. Otherwise, the ordering will respect any pairwise
* orderings that have been set. If the graph of pairwise
* orderings contains cycles, any providers that belong to a cycle
* will not be returned.
*
* @param category the category to be retrieved from.
* @param useOrdering <code>true</code> if pairwise orderings
* should be taken account in ordering the returned objects.
* @param <T> the type of the category.
*
* @return an <code>Iterator</code> containing service provider
* objects from the given category, possibly in order.
*
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
*/
public <T>
Iterator<T>
getServiceProviders(
Class<T>
category,
boolean
useOrdering) {
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
return
reg.
getServiceProviders(
useOrdering);
}
/**
* A simple filter interface used by
* <code>ServiceRegistry.getServiceProviders</code> to select
* providers matching an arbitrary criterion. Classes that
* implement this interface should be defined in order to make use
* of the <code>getServiceProviders</code> method of
* <code>ServiceRegistry</code> that takes a <code>Filter</code>.
*
* @see ServiceRegistry#getServiceProviders(Class, ServiceRegistry.Filter, boolean)
*/
public interface
Filter {
/**
* Returns <code>true</code> if the given
* <code>provider</code> object matches the criterion defined
* by this <code>Filter</code>.
*
* @param provider a service provider <code>Object</code>.
*
* @return true if the provider matches the criterion.
*/
boolean
filter(
Object provider);
}
/**
* Returns an <code>Iterator</code> containing service provider
* objects within a given category that satisfy a criterion
* imposed by the supplied <code>ServiceRegistry.Filter</code>
* object's <code>filter</code> method.
*
* <p> The <code>useOrdering</code> argument controls the
* ordering of the results using the same rules as
* <code>getServiceProviders(Class, boolean)</code>.
*
* @param category the category to be retrieved from.
* @param filter an instance of <code>ServiceRegistry.Filter</code>
* whose <code>filter</code> method will be invoked.
* @param useOrdering <code>true</code> if pairwise orderings
* should be taken account in ordering the returned objects.
* @param <T> the type of the category.
*
* @return an <code>Iterator</code> containing service provider
* objects from the given category, possibly in order.
*
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
*/
public <T>
Iterator<T>
getServiceProviders(
Class<T>
category,
Filter filter,
boolean
useOrdering) {
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
Iterator iter =
getServiceProviders(
category,
useOrdering);
return new
FilterIterator(
iter,
filter);
}
/**
* Returns the currently registered service provider object that
* is of the given class type. At most one object of a given
* class is allowed to be registered at any given time. If no
* registered object has the desired class type, <code>null</code>
* is returned.
*
* @param providerClass the <code>Class</code> of the desired
* service provider object.
* @param <T> the type of the provider.
*
* @return a currently registered service provider object with the
* desired <code>Class</code>type, or <code>null</code> is none is
* present.
*
* @exception IllegalArgumentException if <code>providerClass</code> is
* <code>null</code>.
*/
public <T> T
getServiceProviderByClass(
Class<T>
providerClass) {
if (
providerClass == null) {
throw new
IllegalArgumentException("providerClass == null!");
}
Iterator iter =
categoryMap.
keySet().
iterator();
while (
iter.
hasNext()) {
Class c = (
Class)
iter.
next();
if (
c.
isAssignableFrom(
providerClass)) {
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
c);
T
provider =
reg.
getServiceProviderByClass(
providerClass);
if (
provider != null) {
return
provider;
}
}
}
return null;
}
/**
* Sets a pairwise ordering between two service provider objects
* within a given category. If one or both objects are not
* currently registered within the given category, or if the
* desired ordering is already set, nothing happens and
* <code>false</code> is returned. If the providers previously
* were ordered in the reverse direction, that ordering is
* removed.
*
* <p> The ordering will be used by the
* <code>getServiceProviders</code> methods when their
* <code>useOrdering</code> argument is <code>true</code>.
*
* @param category a <code>Class</code> object indicating the
* category under which the preference is to be established.
* @param firstProvider the preferred provider.
* @param secondProvider the provider to which
* <code>firstProvider</code> is preferred.
* @param <T> the type of the category.
*
* @return <code>true</code> if a previously unset ordering
* was established.
*
* @exception IllegalArgumentException if either provider is
* <code>null</code> or they are the same object.
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
*/
public <T> boolean
setOrdering(
Class<T>
category,
T
firstProvider,
T
secondProvider) {
if (
firstProvider == null ||
secondProvider == null) {
throw new
IllegalArgumentException("provider is null!");
}
if (
firstProvider ==
secondProvider) {
throw new
IllegalArgumentException("providers are the same!");
}
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
if (
reg.
contains(
firstProvider) &&
reg.
contains(
secondProvider)) {
return
reg.
setOrdering(
firstProvider,
secondProvider);
}
return false;
}
/**
* Sets a pairwise ordering between two service provider objects
* within a given category. If one or both objects are not
* currently registered within the given category, or if no
* ordering is currently set between them, nothing happens
* and <code>false</code> is returned.
*
* <p> The ordering will be used by the
* <code>getServiceProviders</code> methods when their
* <code>useOrdering</code> argument is <code>true</code>.
*
* @param category a <code>Class</code> object indicating the
* category under which the preference is to be disestablished.
* @param firstProvider the formerly preferred provider.
* @param secondProvider the provider to which
* <code>firstProvider</code> was formerly preferred.
* @param <T> the type of the category.
*
* @return <code>true</code> if a previously set ordering was
* disestablished.
*
* @exception IllegalArgumentException if either provider is
* <code>null</code> or they are the same object.
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
*/
public <T> boolean
unsetOrdering(
Class<T>
category,
T
firstProvider,
T
secondProvider) {
if (
firstProvider == null ||
secondProvider == null) {
throw new
IllegalArgumentException("provider is null!");
}
if (
firstProvider ==
secondProvider) {
throw new
IllegalArgumentException("providers are the same!");
}
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
if (
reg.
contains(
firstProvider) &&
reg.
contains(
secondProvider)) {
return
reg.
unsetOrdering(
firstProvider,
secondProvider);
}
return false;
}
/**
* Deregisters all service provider object currently registered
* under the given category.
*
* @param category the category to be emptied.
*
* @exception IllegalArgumentException if there is no category
* corresponding to <code>category</code>.
*/
public void
deregisterAll(
Class<?>
category) {
SubRegistry reg = (
SubRegistry)
categoryMap.
get(
category);
if (
reg == null) {
throw new
IllegalArgumentException("category unknown!");
}
reg.
clear();
}
/**
* Deregisters all currently registered service providers from all
* categories.
*/
public void
deregisterAll() {
Iterator iter =
categoryMap.
values().
iterator();
while (
iter.
hasNext()) {
SubRegistry reg = (
SubRegistry)
iter.
next();
reg.
clear();
}
}
/**
* Finalizes this object prior to garbage collection. The
* <code>deregisterAll</code> method is called to deregister all
* currently registered service providers. This method should not
* be called from application code.
*
* @exception Throwable if an error occurs during superclass
* finalization.
*/
public void
finalize() throws
Throwable {
deregisterAll();
super.finalize();
}
}
/**
* A portion of a registry dealing with a single superclass or
* interface.
*/
class
SubRegistry {
ServiceRegistry registry;
Class category;
// Provider Objects organized by partial ordering
final
PartiallyOrderedSet poset = new
PartiallyOrderedSet();
// Class -> Provider Object of that class
final
Map<
Class<?>,
Object>
map = new
HashMap();
final
Map<
Class<?>,
AccessControlContext>
accMap = new
HashMap<>();
public
SubRegistry(
ServiceRegistry registry,
Class category) {
this.
registry =
registry;
this.
category =
category;
}
public boolean
registerServiceProvider(
Object provider) {
Object oprovider =
map.
get(
provider.
getClass());
boolean
present =
oprovider != null;
if (
present) {
deregisterServiceProvider(
oprovider);
}
map.
put(
provider.
getClass(),
provider);
accMap.
put(
provider.
getClass(),
AccessController.
getContext());
poset.
add(
provider);
if (
provider instanceof
RegisterableService) {
RegisterableService rs = (
RegisterableService)
provider;
rs.
onRegistration(
registry,
category);
}
return !
present;
}
/**
* If the provider was not previously registered, do nothing.
*
* @return true if the provider was previously registered.
*/
public boolean
deregisterServiceProvider(
Object provider) {
Object oprovider =
map.
get(
provider.
getClass());
if (
provider ==
oprovider) {
map.
remove(
provider.
getClass());
accMap.
remove(
provider.
getClass());
poset.
remove(
provider);
if (
provider instanceof
RegisterableService) {
RegisterableService rs = (
RegisterableService)
provider;
rs.
onDeregistration(
registry,
category);
}
return true;
}
return false;
}
public boolean
contains(
Object provider) {
Object oprovider =
map.
get(
provider.
getClass());
return
oprovider ==
provider;
}
public boolean
setOrdering(
Object firstProvider,
Object secondProvider) {
return
poset.
setOrdering(
firstProvider,
secondProvider);
}
public boolean
unsetOrdering(
Object firstProvider,
Object secondProvider) {
return
poset.
unsetOrdering(
firstProvider,
secondProvider);
}
public
Iterator getServiceProviders(boolean
useOrdering) {
if (
useOrdering) {
return
poset.
iterator();
} else {
return
map.
values().
iterator();
}
}
public <T> T
getServiceProviderByClass(
Class<T>
providerClass) {
return (T)
map.
get(
providerClass);
}
public void
clear() {
Iterator iter =
map.
values().
iterator();
while (
iter.
hasNext()) {
Object provider =
iter.
next();
iter.
remove();
if (
provider instanceof
RegisterableService) {
RegisterableService rs = (
RegisterableService)
provider;
AccessControlContext acc =
accMap.
get(
provider.
getClass());
if (
acc != null ||
System.
getSecurityManager() == null) {
AccessController.
doPrivileged((
PrivilegedAction<
Void>) () -> {
rs.
onDeregistration(
registry,
category);
return null;
},
acc);
}
}
}
poset.
clear();
accMap.
clear();
}
public void
finalize() {
clear();
}
}
/**
* A class for wrapping <code>Iterators</code> with a filter function.
* This provides an iterator for a subset without duplication.
*/
class
FilterIterator<T> implements
Iterator<T> {
private
Iterator<T>
iter;
private
ServiceRegistry.
Filter filter;
private T
next = null;
public
FilterIterator(
Iterator<T>
iter,
ServiceRegistry.
Filter filter) {
this.
iter =
iter;
this.
filter =
filter;
advance();
}
private void
advance() {
while (
iter.
hasNext()) {
T
elt =
iter.
next();
if (
filter.
filter(
elt)) {
next =
elt;
return;
}
}
next = null;
}
public boolean
hasNext() {
return
next != null;
}
public T
next() {
if (
next == null) {
throw new
NoSuchElementException();
}
T
o =
next;
advance();
return
o;
}
public void
remove() {
throw new
UnsupportedOperationException();
}
}