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	/*
	* Copyright (c) 1997, 2021, 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.security;

	import java.util.*;
	import java.util.stream.Stream;
	import java.util.stream.StreamSupport;

	/**
	* Abstract class representing a collection of Permission objects.
	*
	* <p>With a PermissionCollection, you can:
	* <UL>
	* <LI> add a permission to the collection using the {@code add} method.
	* <LI> check to see if a particular permission is implied in the
	* collection, using the {@code implies} method.
	* <LI> enumerate all the permissions, using the {@code elements} method.
	* </UL>
	*
	* <p>When it is desirable to group together a number of Permission objects
	* of the same type, the {@code newPermissionCollection} method on that
	* particular type of Permission object should first be called. The default
	* behavior (from the Permission class) is to simply return null.
	* Subclasses of class Permission override the method if they need to store
	* their permissions in a particular PermissionCollection object in order
	* to provide the correct semantics when the
	* {@code PermissionCollection.implies} method is called.
	* If a non-null value is returned, that PermissionCollection must be used.
	* If null is returned, then the caller of {@code newPermissionCollection}
	* is free to store permissions of the
	* given type in any PermissionCollection they choose
	* (one that uses a Hashtable, one that uses a Vector, etc).
	*
	* <p>The PermissionCollection returned by the
	* {@code Permission.newPermissionCollection}
	* method is a homogeneous collection, which stores only Permission objects
	* for a given Permission type. A PermissionCollection may also be
	* heterogeneous. For example, Permissions is a PermissionCollection
	* subclass that represents a collection of PermissionCollections.
	* That is, its members are each a homogeneous PermissionCollection.
	* For example, a Permissions object might have a FilePermissionCollection
	* for all the FilePermission objects, a SocketPermissionCollection for all the
	* SocketPermission objects, and so on. Its {@code add} method adds a
	* permission to the appropriate collection.
	*
	* <p>Whenever a permission is added to a heterogeneous PermissionCollection
	* such as Permissions, and the PermissionCollection doesn't yet contain a
	* PermissionCollection of the specified permission's type, the
	* PermissionCollection should call
	* the {@code newPermissionCollection} method on the permission's class
	* to see if it requires a special PermissionCollection. If
	* {@code newPermissionCollection}
	* returns null, the PermissionCollection
	* is free to store the permission in any type of PermissionCollection it
	* desires (one using a Hashtable, one using a Vector, etc.). For example,
	* the Permissions object uses a default PermissionCollection implementation
	* that stores the permission objects in a Hashtable.
	*
	* <p> Subclass implementations of PermissionCollection should assume
	* that they may be called simultaneously from multiple threads,
	* and therefore should be synchronized properly. Furthermore,
	* Enumerations returned via the {@code elements} method are
	* not <em>fail-fast</em>. Modifications to a collection should not be
	* performed while enumerating over that collection.
	*
	* @see Permission
	* @see Permissions
	*
	*
	* @author Roland Schemers
	* @since 1.2
	*/

	public abstract class PermissionCollection implements java.io.Serializable {

	@java.io.Serial
	private static final long serialVersionUID = -6727011328946861783L;

	/**
	* Whether this permission collection is read-only.
	* <p>
	* If set, the {@code add} method will throw an exception.
	*/
	private volatile boolean readOnly;

	/**
	* Constructor for subclasses to call.
	*/
	public PermissionCollection() {}

	/**
	* Adds a permission object to the current collection of permission objects.
	*
	* @param permission the Permission object to add.
	*
	* @throws SecurityException if this PermissionCollection object
	* has been marked readonly
	* @throws IllegalArgumentException if this PermissionCollection
	* object is a homogeneous collection and the permission
	* is not of the correct type.
	*/
	public abstract void add(Permission permission);

	/**
	* Checks to see if the specified permission is implied by
	* the collection of Permission objects held in this PermissionCollection.
	*
	* @param permission the Permission object to compare.
	*
	* @return true if "permission" is implied by the permissions in
	* the collection, false if not.
	*/
	public abstract boolean implies(Permission permission);

	/**
	* Returns an enumeration of all the Permission objects in the collection.
	*
	* @return an enumeration of all the Permissions.
	* @see #elementsAsStream()
	*/
	public abstract Enumeration<Permission> elements();

	/**
	* Returns a stream of all the Permission objects in the collection.
	*
	* <p> The collection should not be modified (see {@link #add}) during the
	* execution of the terminal stream operation. Otherwise, the result of the
	* terminal stream operation is undefined.
	*
	* @implSpec
	* The default implementation creates a stream whose source is derived from
	* the enumeration returned from a call to {@link #elements()}.
	*
	* @return a stream of all the Permissions.
	* @since 9
	*/
	public Stream<Permission> elementsAsStream() {
	int characteristics = isReadOnly()
	? Spliterator.NONNULL \| Spliterator.IMMUTABLE
	: Spliterator.NONNULL;
	return StreamSupport.stream(
	Spliterators.spliteratorUnknownSize(
	elements().asIterator(), characteristics),
	false);
	}

	/**
	* Marks this PermissionCollection object as "readonly". After
	* a PermissionCollection object
	* is marked as readonly, no new Permission objects can be added to it
	* using {@code add}.
	*/
	public void setReadOnly() {
	readOnly = true;
	}

	/**
	* Returns true if this PermissionCollection object is marked as readonly.
	* If it is readonly, no new Permission objects can be added to it
	* using {@code add}.
	*
	* <p>By default, the object is <i>not</i> readonly. It can be set to
	* readonly by a call to {@code setReadOnly}.
	*
	* @return true if this PermissionCollection object is marked as readonly,
	* false otherwise.
	*/
	public boolean isReadOnly() {
	return readOnly;
	}

	/**
	* Returns a string describing this PermissionCollection object,
	* providing information about all the permissions it contains.
	* The format is:
	* <pre>
	* super.toString() (
	* // enumerate all the Permission
	* // objects and call toString() on them,
	* // one per line..
	* )</pre>
	*
	* {@code super.toString} is a call to the {@code toString}
	* method of this
	* object's superclass, which is Object. The result is
	* this PermissionCollection's type name followed by this object's
	* hashcode, thus enabling clients to differentiate different
	* PermissionCollections object, even if they contain the same permissions.
	*
	* @return information about this PermissionCollection object,
	* as described above.
	*
	*/
	public String toString() {
	Enumeration<Permission> enum_ = elements();
	StringBuilder sb = new StringBuilder();
	sb.append(super.toString()+" (\n");
	while (enum_.hasMoreElements()) {
	try {
	sb.append(" ");
	sb.append(enum_.nextElement().toString());
	sb.append("\n");
	} catch (NoSuchElementException e){
	// ignore
	}
	}
	sb.append(")\n");
	return sb.toString();
	}
	}

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