001/* PermissionCollection.java -- A collection of permission objects
002   Copyright (C) 1998, 2001, 2002, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
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017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
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036exception statement from your version. */
037
038package java.security;
039
040import gnu.java.lang.CPStringBuilder;
041
042import java.io.Serializable;
043import 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 */
079public 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