# Class Permission

java.lang.Object
java.security.Permission

All Implemented Interfaces:
  `Serializable, Guard`

Direct Known Subclasses:
  `AllPermission, BasicPermission, CardPermission, FilePermission, MBeanPermission, PrivateCredentialPermission, ServicePermission, SocketPermission, UnresolvedPermission, URLPermission`

public abstract class Permission extends Object implements Guard, Serializable
Abstract class for representing access to a system resource. All permissions have a name (whose interpretation depends on the subclass), as well as abstract functions for defining the semantics of the particular Permission subclass.

Most `Permission` objects also include an "actions" list that tells the actions that are permitted for the object. For example, for a `java.io.FilePermission` object, the permission name is the pathname of a file (or directory), and the actions list (such as "read, write") specifies which actions are granted for the specified file (or for files in the specified directory). The actions list is optional for `Permission` objects, such as `java.lang.RuntimePermission`, that don't need such a list; you either have the named permission (such as "system.exit") or you don't.

An important method that must be implemented by each subclass is the `implies` method to compare Permissions. Basically, "permission p1 implies permission p2" means that if one is granted permission p1, one is naturally granted permission p2. Thus, this is not an equality test, but rather more of a subset test.

`Permission` objects are similar to `String` objects in that they are immutable once they have been created. Subclasses should not provide methods that can change the state of a permission once it has been created.

Since:
  1.2
See Also:
  - `Permissions`
  - `PermissionCollection`
  - Serialized Form

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `Permission(String name)`
  Constructs a permission with the specified name.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `checkGuard(Object object)`
  Implements the guard interface for a permission.
  `abstract boolean`
  `equals(Object obj)`
  Checks two `Permission` objects for equality.
  `abstract String`
  `getActions()`
  Returns the actions as a `String`.
  `final String`
  `getName()`
  Returns the name of this `Permission`.
  `abstract int`
  `hashCode()`
  Returns the hash code value for this `Permission` object.
  `abstract boolean`
  `implies(Permission permission)`
  Checks if the specified permission's actions are "implied by" this object's actions.
  `PermissionCollection`
  `newPermissionCollection()`
  Returns an empty `PermissionCollection` for a given `Permission` object, or `null` if one is not defined.
  `String`
  `toString()`
  Returns a string describing this `Permission`.

  ### Methods declared in class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### Permission

    public Permission(String name)
    Constructs a permission with the specified name.
    Parameters:
      `name` - name of the `Permission` object being created.

- ## Method Details

  - ### checkGuard

    public void checkGuard(Object object) throws SecurityException
    Implements the guard interface for a permission. Returns silently if access is granted. Otherwise, throws a `SecurityException`.
    Specified by:
      `checkGuard` in interface `Guard`
    API Note:
      This method originally threw a `SecurityException` if a security manager was enabled and the requested access, specified by this permission, was not permitted. The Security Manager is no longer supported; thus, this method always throws a `SecurityException`.
    Parameters:
      `object` - the object being guarded (currently ignored).
    Throws:
      `SecurityException` - always
    See Also:
      - `Guard`
      - `GuardedObject`

  - ### implies

    public abstract boolean implies(Permission permission)
    Checks if the specified permission's actions are "implied by" this object's actions.

    This must be implemented by subclasses of `Permission`, as they are the only ones that can impose semantics on a `Permission` object.

    Parameters:
      `permission` - the permission to check against.
    Returns:
      `true` if the specified permission is implied by this object, `false` if not.

  - ### equals

    public abstract boolean equals(Object obj)
    Checks two `Permission` objects for equality.

    Do not use the `equals` method for making access control decisions; use the `implies` method.

    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - the object we are testing for equality with this object.
    Returns:
      `true` if both `Permission` objects are equivalent.
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public abstract int hashCode()
    Returns the hash code value for this `Permission` object.

    The required `hashCode` behavior for `Permission` Objects is the following:

    - Whenever it is invoked on the same `Permission` object more than once during an execution of a Java application, the `hashCode` method must consistently return the same integer. This integer need not remain consistent from one execution of an application to another execution of the same application.
    - If two `Permission` objects are equal according to the `equals` method, then calling the `hashCode` method on each of the two `Permission` objects must produce the same integer result.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      a hash code value for this object.
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`

  - ### getName

    public final String getName()
    Returns the name of this `Permission`. For example, in the case of a `java.io.FilePermission`, the name will be a pathname.
    Returns:
      the name of this `Permission`.

  - ### getActions

    public abstract String getActions()
    Returns the actions as a `String`. This is abstract so subclasses can defer creating a `String` representation until one is needed. Subclasses should always return actions in what they consider to be their canonical form. For example, two FilePermission objects created via the following:

          perm1 = new FilePermission(p1,"read,write");
          perm2 = new FilePermission(p2,"write,read");

    both return "read,write" when the `getActions` method is invoked.
    Returns:
      the actions of this `Permission`.

  - ### newPermissionCollection

    public PermissionCollection newPermissionCollection()
    Returns an empty `PermissionCollection` for a given `Permission` object, or `null` if one is not defined. Subclasses of class `Permission` should override this 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 `null` is returned, then the caller of this method is free to store permissions of this type in any `PermissionCollection` they choose (one that uses a Hashtable, one that uses a Vector, etc.).
    Returns:
      a new `PermissionCollection` object for this type of `Permission`, or `null` if one is not defined.

  - ### toString

    public String toString()
    Returns a string describing this `Permission`. The convention is to specify the class name, the permission name, and the actions in the following format: '("ClassName" "name" "actions")', or '("ClassName" "name")' if actions list is `null` or empty.
    Overrides:
      `toString` in class `Object`
    Returns:
      information about this `Permission`.