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 * accompanied this code).

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package java.security;

/**

 * 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.

 *

 * <p>Most Permission objects also include an "actions" list that tells the actions

 * that are permitted for the object.  For example,

 * for a {@code 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

 * {@code java.lang.RuntimePermission},

 * that don't need such a list; you either have the named permission (such

 * as "system.exit") or you don't.

 *

 * <p>An important method that must be implemented by each subclass is

 * the {@code 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.

 *

 * <P> 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.

 *

 * @see Permissions

 * @see PermissionCollection

 *

 *

 * @author Marianne Mueller

 * @author Roland Schemers

 * @since 1.2

 */

public abstract class Permission implements Guard, java.io.Serializable {

    private static final long serialVersionUID = -5636570222231596674L;

    private String name;

    /**

     * Constructs a permission with the specified name.

     *

     * @param name name of the Permission object being created.

     *

     */

    public Permission(String name) {

        this.name = name;

    }

    /**

     * Implements the guard interface for a permission. The

     * {@code SecurityManager.checkPermission} method is called,

     * passing this permission object as the permission to check.

     * Returns silently if access is granted. Otherwise, throws

     * a SecurityException.

     *

     * @param object the object being guarded (currently ignored).

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow access.

     *

     * @see Guard

     * @see GuardedObject

     * @see SecurityManager#checkPermission

     *

     */

    public void checkGuard(Object object) throws SecurityException {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) sm.checkPermission(this);

    }

    /**

     * Checks if the specified permission's actions are "implied by"

     * this object's actions.

     * <P>

     * This must be implemented by subclasses of Permission, as they are the

     * only ones that can impose semantics on a Permission object.

     *

     * <p>The {@code implies} method is used by the AccessController to determine

     * whether or not a requested permission is implied by another permission that

     * is known to be valid in the current execution context.

     *

     * @param permission the permission to check against.

     *

     * @return true if the specified permission is implied by this object,

     * false if not.

     */

    public abstract boolean implies(Permission permission);

    /**

     * Checks two Permission objects for equality.

     * <P>

     * Do not use the {@code equals} method for making access control

     * decisions; use the {@code implies} method.

     *

     * @param obj the object we are testing for equality with this object.

     *

     * @return true if both Permission objects are equivalent.

     */

    public abstract boolean equals(Object obj);

    /**

     * Returns the hash code value for this Permission object.

     * <P>

     * The required {@code hashCode} behavior for Permission Objects is

     * the following:

     * <ul>

     * <li>Whenever it is invoked on the same Permission object more than

     *     once during an execution of a Java application, the

     *     {@code 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.

     * <li>If two Permission objects are equal according to the

     *     {@code equals}

     *     method, then calling the {@code hashCode} method on each of the

     *     two Permission objects must produce the same integer result.

     * </ul>

     *

     * @return a hash code value for this object.

     */

    public abstract int hashCode();

    /**

     * Returns the name of this Permission.

     * For example, in the case of a {@code java.io.FilePermission},

     * the name will be a pathname.

     *

     * @return the name of this Permission.

     *

     */

    public final String getName() {

        return name;

    }

    /**

     * 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:

     *

     * <pre>

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

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

     * </pre>

     *

     * both return

     * "read,write" when the {@code getActions} method is invoked.

     *

     * @return the actions of this Permission.

     *

     */

    public abstract String getActions();

    /**

     * 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 {@code 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).

     *

     * @return a new PermissionCollection object for this type of Permission, or

     * null if one is not defined.

     */

    public PermissionCollection newPermissionCollection() {

        return null;

    }

    /**

     * 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.

     *

     * @return information about this Permission.

     */

    public String toString() {

        String actions = getActions();

        if (actions == null || actions.isEmpty()) { // OPTIONAL

            return "(\"" + getClass().getName() + "\" \"" + name + "\")";

        } else {

            return "(\"" + getClass().getName() + "\" \"" + name +

                 "\" \"" + actions + "\")";

        }

    }

}