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* accompanied this code).
*
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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</code> method.
* <LI> check to see if a particular permission is implied in the
* collection, using the <code>implies</code> method.
* <LI> enumerate all the permissions, using the <code>elements</code> method.
* </UL>
* <P>
*
* <p>When it is desirable to group together a number of Permission objects
* of the same type, the <code>newPermissionCollection</code> 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</code> 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</code>
* 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</code>
* 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</code> 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</code> method on the permission's class
* to see if it requires a special PermissionCollection. If
* <code>newPermissionCollection</code>
* 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</code> method are
* not <em>fail-fast</em>. 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
*/
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</code>.
*/
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</code>.
*
* <p>By default, the object is <i>not</i> readonly. It can be set to
* readonly by a call to <code>setReadOnly</code>.
*
* @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</code> is a call to the <code>toString</code>
* 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();
}
}