001    /* PermissionCollection.java -- A collection of permission objects
002       Copyright (C) 1998, 2001, 2002, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
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037    
038    package java.security;
039    
040    import gnu.java.lang.CPStringBuilder;
041    
042    import java.io.Serializable;
043    import java.util.Enumeration;
044    
045    /**
046     * This class models a group of Java permissions.  It has convenient
047     * methods for determining whether or not a given permission is implied
048     * by any of the permissions in this collection.
049     *
050     * <p>Some care must be taken in storing permissions.  First, a collection of
051     * the appropriate type must be created.  This is done by calling the
052     * <code>newPermissionCollection</code> method on an object of the
053     * permission class you wish to add to the collection.  If this method
054     * returns <code>null</code>, any type of <code>PermissionCollection</code>
055     * can be used to store permissions of that type.  However, if a
056     * <code>PermissionCollection</code> collection object is returned, that
057     * type must be used.
058     *
059     * <p>A <code>PermissionCollection</code> returned by the
060     * <code>newPermissionCollection</code> method in a subclass of
061     * <code>Permission</code> is a homogeneous collection.  It only will
062     * hold permissions of one specified type - instances of the class that
063     * created it.  Not all <code>PermissionCollection</code> subclasses
064     * have to hold permissions of only one type however.  For example,
065     * the <code>Permissions</code> class holds permissions of many types.
066     *
067     * <p>Since the <code>newPermissionCollection</code> in <code>Permission</code>
068     * itself returns <code>null</code>, by default a permission can be stored
069     * in any type of collection unless it overrides that method to create its
070     * own collection type.
071     *
072     * @author Aaron M. Renn (arenn@urbanophile.com)
073     * @author Eric Blake (ebb9@email.byu.edu)
074     * @see Permission
075     * @see Permissions
076     * @since 1.1
077     * @status updated to 1.4
078     */
079    public abstract class PermissionCollection implements Serializable
080    {
081      /**
082       * Compatible with JDK 1.1+.
083       */
084      private static final long serialVersionUID = -6727011328946861783L;
085    
086      /**
087       * Indicates whether or not this collection is read only.
088       *
089       * @serial if the collection is read-only
090       */
091      private boolean readOnly;
092    
093      /**
094       * Create a new collection.
095       */
096      public PermissionCollection()
097      {
098      }
099    
100      /**
101       * This method adds a new <code>Permission</code> object to the collection.
102       *
103       * @param perm the <code>Permission</code> to add
104       *
105       * @throws SecurityException if the collection is marked read only
106       * @throws IllegalArgumentException if perm is of the wrong type
107       */
108      public abstract void add(Permission perm);
109    
110      /**
111       * This method tests whether the specified <code>Permission</code> object is
112       * implied by this collection of <code>Permission</code> objects.
113       *
114       * @param perm the <code>Permission</code> object to test
115       * @return true if the collection implies perm
116       */
117      public abstract boolean implies(Permission perm);
118    
119      /**
120       * This method returns an <code>Enumeration</code> of all the objects in
121       * this collection.
122       *
123       * @return an <code>Enumeration</code> of this collection's objects
124       */
125      public abstract Enumeration<Permission> elements();
126    
127      /**
128       * This method sets this <code>PermissionCollection</code> object to be
129       * read only.  No further permissions can be added to it after calling this
130       * method.
131       */
132      public void setReadOnly()
133      {
134        readOnly = true;
135      }
136    
137      /**
138       * This method tests whether or not this <code>PermissionCollection</code>
139       * object is read only.
140       *
141       * @return true if this collection is read only
142       */
143      public boolean isReadOnly()
144      {
145        return readOnly;
146      }
147    
148      /**
149       * This method returns a <code>String</code> representation of this
150       * collection.  It is formed by:
151       * <pre>
152       * super.toString()" (\n"
153       *   // enumerate all permissions, one per line
154       * ")\n"
155       * </pre>
156       *
157       * @return a <code>String</code> representing this object
158       */
159      public String toString()
160      {
161        CPStringBuilder sb = new CPStringBuilder(super.toString());
162    
163        sb.append(" (\n");
164        Enumeration<Permission> e = elements();
165        while (e.hasMoreElements())
166          sb.append(' ').append(e.nextElement()).append('\n');
167        return sb.append(")\n").toString();
168      }
169    } // class PermissionCollection