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.reflect.generics.scope;
  27 
  28 import java.lang.reflect.TypeVariable;
  29 
  30 /**
  31  * This class is used to provide enclosing scopes for top level classes.
  32  * We cannot use <tt>null</tt> to represent such a scope, since the
  33  * enclosing scope is computed lazily, and so the field storing it is
  34  * null until it has been computed. Therefore, <tt>null</tt> is reserved
  35  * to represent an as-yet-uncomputed scope, and cannot be used for any
  36  * other kind of scope.
  37  */
  38 public class DummyScope implements Scope {
  39     // Caches the unique instance of this class; instances contain no data
  40     // so we can use the singleton pattern
  41     private static final DummyScope singleton = new DummyScope();
  42 
  43     // constructor is private to enforce use of factory method
  44     private DummyScope(){}
  45 
  46     /**
  47      * Factory method. Enforces the singleton pattern - only one
  48      * instance of this class ever exists.
  49      */
  50     public static DummyScope make() {
  51         return singleton;
  52     }
  53 
  54     /**
  55      * Lookup a type variable in the scope, using its name. Always returns
  56      * <tt>null</tt>.
  57      * @param name - the name of the type variable being looked up
  58      * @return  null
  59      */
  60     public TypeVariable<?> lookup(String name) {return null;}
  61 }