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PermissionCollection.javaAPI DocJava SE 5 API6717Fri Aug 26 14:57:14 BST 2005java.security

PermissionCollection

public abstract class PermissionCollection extends Object implements Serializable
Abstract class representing a collection of Permission objects.

With a PermissionCollection, you can:

  • add a permission to the collection using the add method.
  • check to see if a particular permission is implied in the collection, using the implies method.
  • enumerate all the permissions, using the elements method.

When it is desirable to group together a number of Permission objects of the same type, the newPermissionCollection 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 PermissionCollection.implies method is called. If a non-null value is returned, that PermissionCollection must be used. If null is returned, then the caller of newPermissionCollection 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).

The PermissionCollection returned by the Permission.newPermissionCollection 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 add method adds a permission to the appropriate collection.

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 newPermissionCollection method on the permission's class to see if it requires a special PermissionCollection. If newPermissionCollection 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.

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 elements method are not fail-fast. Modifications to a collection should not be performed while enumerating over that collection.

see
Permission
see
Permissions
version
1.35 04/05/05
author
Roland Schemers

Fields Summary
private static final long
serialVersionUID
private volatile boolean
readOnly
Constructors Summary
Methods Summary
public abstract voidadd(java.security.Permission permission)
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 java.util.Enumerationelements()
Returns an enumeration of all the Permission objects in the collection.
return
an enumeration of all the Permissions.
public abstract booleanimplies(java.security.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 booleanisReadOnly()
Returns true if this PermissionCollection object is marked as readonly.
If it is readonly, no new Permission objects can be added to it
using add.


By default, the object is not readonly. It can be set to
readonly by a call to setReadOnly.
return
true if this PermissionCollection object is marked as readonly,
false otherwise.
	return readOnly;
    
public voidsetReadOnly()
Marks this PermissionCollection object as "readonly". After
a PermissionCollection object
is marked as readonly, no new Permission objects can be added to it
using add.

                                                                       
        

                                                   
        

                           
       

                                  
       
	readOnly = true;
    
public java.lang.StringtoString()
Returns a string describing this PermissionCollection object,
providing information about all the permissions it contains.
The format is:

super.toString() (
// enumerate all the Permission
// objects and call toString() on them,
// one per line..
)


super.toString is a call to the toString
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.
	Enumeration 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();