/* PermissionCollection.java -- A collection of permission objects
   Copyright (C) 1998, 2001, 2002, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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General Public License for more details.

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02110-1301 USA.

Linking this library statically or dynamically with other modules is
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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terms of your choice, provided that you also meet, for each linked
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package java.security;

import gnu.java.lang.CPStringBuilder;

import java.io.Serializable;
import java.util.Enumeration;

/**
 * This class models a group of Java permissions.  It has convenient
 * methods for determining whether or not a given permission is implied
 * by any of the permissions in this collection.
 *
 * <p>Some care must be taken in storing permissions.  First, a collection of
 * the appropriate type must be created.  This is done by calling the
 * <code>newPermissionCollection</code> method on an object of the
 * permission class you wish to add to the collection.  If this method
 * returns <code>null</code>, any type of <code>PermissionCollection</code>
 * can be used to store permissions of that type.  However, if a
 * <code>PermissionCollection</code> collection object is returned, that
 * type must be used.
 *
 * <p>A <code>PermissionCollection</code> returned by the
 * <code>newPermissionCollection</code> method in a subclass of
 * <code>Permission</code> is a homogeneous collection.  It only will
 * hold permissions of one specified type - instances of the class that
 * created it.  Not all <code>PermissionCollection</code> subclasses
 * have to hold permissions of only one type however.  For example,
 * the <code>Permissions</code> class holds permissions of many types.
 *
 * <p>Since the <code>newPermissionCollection</code> in <code>Permission</code>
 * itself returns <code>null</code>, by default a permission can be stored
 * in any type of collection unless it overrides that method to create its
 * own collection type.
 *
 * @author Aaron M. Renn (arenn@urbanophile.com)
 * @author Eric Blake (ebb9@email.byu.edu)
 * @see Permission
 * @see Permissions
 * @since 1.1
 * @status updated to 1.4
 */
public abstract class PermissionCollection implements Serializable
{
  /**
   * Compatible with JDK 1.1+.
   */
  private static final long serialVersionUID = -6727011328946861783L;

  /**
   * Indicates whether or not this collection is read only.
   *
   * @serial if the collection is read-only
   */
  private boolean readOnly;

  /**
   * Create a new collection.
   */
  public PermissionCollection()
  {
  }

  /**
   * This method adds a new <code>Permission</code> object to the collection.
   *
   * @param perm the <code>Permission</code> to add
   *
   * @throws SecurityException if the collection is marked read only
   * @throws IllegalArgumentException if perm is of the wrong type
   */
  public abstract void add(Permission perm);

  /**
   * This method tests whether the specified <code>Permission</code> object is
   * implied by this collection of <code>Permission</code> objects.
   *
   * @param perm the <code>Permission</code> object to test
   * @return true if the collection implies perm
   */
  public abstract boolean implies(Permission perm);

  /**
   * This method returns an <code>Enumeration</code> of all the objects in
   * this collection.
   *
   * @return an <code>Enumeration</code> of this collection's objects
   */
  public abstract Enumeration<Permission> elements();

  /**
   * This method sets this <code>PermissionCollection</code> object to be
   * read only.  No further permissions can be added to it after calling this
   * method.
   */
  public void setReadOnly()
  {
    readOnly = true;
  }

  /**
   * This method tests whether or not this <code>PermissionCollection</code>
   * object is read only.
   *
   * @return true if this collection is read only
   */
  public boolean isReadOnly()
  {
    return readOnly;
  }

  /**
   * This method returns a <code>String</code> representation of this
   * collection.  It is formed by:
   * <pre>
   * super.toString()" (\n"
   *   // enumerate all permissions, one per line
   * ")\n"
   * </pre>
   *
   * @return a <code>String</code> representing this object
   */
  public String toString()
  {
    CPStringBuilder sb = new CPStringBuilder(super.toString());

    sb.append(" (\n");
    Enumeration<Permission> e = elements();
    while (e.hasMoreElements())
      sb.append(' ').append(e.nextElement()).append('\n');
    return sb.append(")\n").toString();
  }
} // class PermissionCollection