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.
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013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
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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
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031 independent module, the terms and conditions of the license of that
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036 exception statement from your version. */
037
038 package java.security;
039
040 import java.io.Serializable;
041 import java.util.Enumeration;
042
043 /**
044 * This class models a group of Java permissions. It has convenient
045 * methods for determining whether or not a given permission is implied
046 * by any of the permissions in this collection.
047 *
048 * <p>Some care must be taken in storing permissions. First, a collection of
049 * the appropriate type must be created. This is done by calling the
050 * <code>newPermissionCollection</code> method on an object of the
051 * permission class you wish to add to the collection. If this method
052 * returns <code>null</code>, any type of <code>PermissionCollection</code>
053 * can be used to store permissions of that type. However, if a
054 * <code>PermissionCollection</code> collection object is returned, that
055 * type must be used.
056 *
057 * <p>A <code>PermissionCollection</code> returned by the
058 * <code>newPermissionCollection</code> method in a subclass of
059 * <code>Permission</code> is a homogeneous collection. It only will
060 * hold permissions of one specified type - instances of the class that
061 * created it. Not all <code>PermissionCollection</code> subclasses
062 * have to hold permissions of only one type however. For example,
063 * the <code>Permissions</code> class holds permissions of many types.
064 *
065 * <p>Since the <code>newPermissionCollection</code> in <code>Permission</code>
066 * itself returns <code>null</code>, by default a permission can be stored
067 * in any type of collection unless it overrides that method to create its
068 * own collection type.
069 *
070 * @author Aaron M. Renn (arenn@urbanophile.com)
071 * @author Eric Blake (ebb9@email.byu.edu)
072 * @see Permission
073 * @see Permissions
074 * @since 1.1
075 * @status updated to 1.4
076 */
077 public abstract class PermissionCollection implements Serializable
078 {
079 /**
080 * Compatible with JDK 1.1+.
081 */
082 private static final long serialVersionUID = -6727011328946861783L;
083
084 /**
085 * Indicates whether or not this collection is read only.
086 *
087 * @serial if the collection is read-only
088 */
089 private boolean readOnly;
090
091 /**
092 * Create a new collection.
093 */
094 public PermissionCollection()
095 {
096 }
097
098 /**
099 * This method adds a new <code>Permission</code> object to the collection.
100 *
101 * @param perm the <code>Permission</code> to add
102 *
103 * @throws SecurityException if the collection is marked read only
104 * @throws IllegalArgumentException if perm is of the wrong type
105 */
106 public abstract void add(Permission perm);
107
108 /**
109 * This method tests whether the specified <code>Permission</code> object is
110 * implied by this collection of <code>Permission</code> objects.
111 *
112 * @param perm the <code>Permission</code> object to test
113 * @return true if the collection implies perm
114 */
115 public abstract boolean implies(Permission perm);
116
117 /**
118 * This method returns an <code>Enumeration</code> of all the objects in
119 * this collection.
120 *
121 * @return an <code>Enumeration</code> of this collection's objects
122 */
123 public abstract Enumeration<Permission> elements();
124
125 /**
126 * This method sets this <code>PermissionCollection</code> object to be
127 * read only. No further permissions can be added to it after calling this
128 * method.
129 */
130 public void setReadOnly()
131 {
132 readOnly = true;
133 }
134
135 /**
136 * This method tests whether or not this <code>PermissionCollection</code>
137 * object is read only.
138 *
139 * @return true if this collection is read only
140 */
141 public boolean isReadOnly()
142 {
143 return readOnly;
144 }
145
146 /**
147 * This method returns a <code>String</code> representation of this
148 * collection. It is formed by:
149 * <pre>
150 * super.toString()" (\n"
151 * // enumerate all permissions, one per line
152 * ")\n"
153 * </pre>
154 *
155 * @return a <code>String</code> representing this object
156 */
157 public String toString()
158 {
159 StringBuffer sb = new StringBuffer(super.toString());
160
161 sb.append(" (\n");
162 Enumeration<Permission> e = elements();
163 while (e.hasMoreElements())
164 sb.append(' ').append(e.nextElement()).append('\n');
165 return sb.append(")\n").toString();
166 }
167 } // class PermissionCollection