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1   /*
2    * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package sun.font;
27  
28  /*
29   * This class is used so that a java.awt.Font does not directly
30   * reference a Font2D object. This introduces occasional minor
31   * de-referencing overhead but increases robustness of the
32   * implementation when "bad fonts" are encountered.
33   * A handle is created by a Font2D constructor and references
34   * the Font2D itself. In the event that the Font2D implementation
35   * determines it the font resource has errors (a bad font file)
36   * it makes its handle point at another "stable" Font2D.
37   * Once all referers no longer have a reference to the Font2D it
38   * may be GC'd and its resources freed.
39   * This does not immediately help in the case that objects are
40   * already using a bad Font2D (ie have already dereferenced the
41   * handle) so there is a window for more problems. However this
42   * is already the case as this is the code which must detect the
43   * problem.
44   * However there is also the possibility of intercepting problems
45   * even when a font2D reference is already directly held. Certain
46   * validation points may check that font2Dhandle.font2D == font2D
47   * If this is not true, then this font2D is not valid. Arguably
48   * this check also just needs to be a de-referencing assignment :
49   * font2D = font2DHandle.font2D.
50   * The net effect of these steps is that very soon after a font
51   * is identified as bad, that references and uses of it will be
52   * eliminated.
53   * In the initial implementation a Font2DHandle is what is held by
54   * - java.awt.Font
55   * - FontManager.initialisedFonts map
56   * Font2D is held by
57   * - FontFamily objects
58   * - FontManager.registeredFonts map
59   * - FontInfo object on a SunGraphics2D
60   *
61   * On discovering a bad font, all but the latter remove references to
62   * the font. See FontManager.deRegisterBadFont(Font2D)
63   */
64  
65  public final class Font2DHandle {
66  
67      public Font2D font2D;
68  
69      public Font2DHandle(Font2D font) {
70          font2D = font;
71      }
72  }