Java example source code file (PermissionCollection.java)

This example Java source code file (PermissionCollection.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

enumeration, nosuchelementexception, permissioncollection, string, stringbuilder, util

The PermissionCollection.java Java example source code

/*
 * Copyright (c) 1997, 2013, 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.*;

/**
 * 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.  Modifications to a collection should not be
 * performed while enumerating over that collection.
 *
 * @see Permission
 * @see Permissions
 *
 *
 * @author Roland Schemers
 */

public abstract class PermissionCollection implements java.io.Serializable {

    private static final long serialVersionUID = -6727011328946861783L;

    // when set, add will throw an exception.
    private volatile boolean readOnly;

    /**
     * Adds a permission object to the current collection of permission objects.
     *
     * @param permission the Permission object to add.
     *
     * @exception SecurityException -  if this PermissionCollection object
     *                                 has been marked readonly
     * @exception 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.
     */
    public abstract Enumeration<Permission> elements();

    /**
     * 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 not 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();
    }
}