CascadingMap


1   /*******************************************************************************
2    * Copyright (c) 2004, 2006 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    *
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.ui.internal.themes;
12  
13  import java.util.Collections  ;
14  import java.util.HashSet  ;
15  import java.util.Map  ;
16  import java.util.Set  ;
17  
18  /**
19   * @since 3.0
20   */
21  public class CascadingMap {
22  
23      private Map   base, override;
24  
25      /** 
26       * @param base the base (default) map
27       * @param override the override map
28       */
29      public CascadingMap(Map   base, Map   override) {
30          this.base = base;
31          this.override = override;
32      }
33  
34      /**
35       * Return the union of the parent and child key sets.  
36       * 
37       * @return the union.  This set is read only.
38       */
39      public Set   keySet() {
40          Set   keySet = new HashSet  (base.keySet());
41          keySet.addAll(override.keySet());
42          return Collections.unmodifiableSet(keySet);
43      }
44  
45      /**
46       * Get the value.  Preference will be given to entries in the override map.
47       * 
48       * @param key the key
49       * @return the value
50       */
51      public Object   get(Object   key) {
52          if (override.containsKey(key)) {
53              return override.get(key);
54          }
55          return base.get(key);
56      }
57  }
58
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