libjava/java/security/PermissionCollection.java

   1 /* PermissionCollection.java -- A collection of permission objects
   2    Copyright (C) 1998, 2001, 2002, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.security;
  39
  40 import java.io.Serializable;
  41 import java.util.Enumeration;
  42
  43 /**
  44  * This class models a group of Java permissions.  It has convenient
  45  * methods for determining whether or not a given permission is implied
  46  * by any of the permissions in this collection.
  47  *
  48  * <p>Some care must be taken in storing permissions.  First, a collection of
  49  * the appropriate type must be created.  This is done by calling the
  50  * <code>newPermissionCollection</code> method on an object of the
  51  * permission class you wish to add to the collection.  If this method
  52  * returns <code>null</code>, any type of <code>PermissionCollection</code>
  53  * can be used to store permissions of that type.  However, if a
  54  * <code>PermissionCollection</code> collection object is returned, that
  55  * type must be used.
  56  *
  57  * <p>A <code>PermissionCollection</code> returned by the
  58  * <code>newPermissionCollection</code> method in a subclass of
  59  * <code>Permission</code> is a homogeneous collection.  It only will
  60  * hold permissions of one specified type - instances of the class that
  61  * created it.  Not all <code>PermissionCollection</code> subclasses
  62  * have to hold permissions of only one type however.  For example,
  63  * the <code>Permissions</code> class holds permissions of many types.
  64  *
  65  * <p>Since the <code>newPermissionCollection</code> in <code>Permission</code>
  66  * itself returns <code>null</code>, by default a permission can be stored
  67  * in any type of collection unless it overrides that method to create its
  68  * own collection type.
  69  *
  70  * @author Aaron M. Renn (arenn@urbanophile.com)
  71  * @author Eric Blake (ebb9@email.byu.edu)
  72  * @see Permission
  73  * @see Permissions
  74  * @since 1.1
  75  * @status updated to 1.4
  76  */
  77 public abstract class PermissionCollection implements Serializable
  78 {
  79   /**
  80    * Compatible with JDK 1.1+.
  81    */
  82   private static final long serialVersionUID = -6727011328946861783L;
  83
  84   /**
  85    * Indicates whether or not this collection is read only.
  86    *
  87    * @serial if the collection is read-only
  88    */
  89   private boolean readOnly;
  90
  91   /**
  92    * Create a new collection.
  93    */
  94   public PermissionCollection()
  95   {
  96   }
  97
  98   /**
  99    * 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 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 e = elements();
 163     while (e.hasMoreElements())
 164       sb.append(' ').append(e.nextElement()).append('\n');
 165     return sb.append(")\n").toString();
 166   }
 167 } // class PermissionCollection