MapCache


1   /*
2    * FindBugs - Find Bugs in Java programs
3    * Copyright (C) 2005, University of Maryland
4    * 
5    * This library is free software; you can redistribute it and/or
6    * modify it under the terms of the GNU Lesser General Public
7    * License as published by the Free Software Foundation; either
8    * version 2.1 of the License, or (at your option) any later version.
9    * 
10   * This library is distributed in the hope that it will be useful,
11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   * Lesser General Public License for more details.
14   * 
15   * You should have received a copy of the GNU Lesser General Public
16   * License along with this library; if not, write to the Free Software
17   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
18   */
19  
20  package edu.umd.cs.findbugs.util;
21  
22  import java.util.LinkedHashMap  ;
23  import java.util.Map  ;
24  
25  import org.apache.bcel.classfile.JavaClass;
26  
27  /**
28   * Provide a HashMap that can only grow to a specified maximum capacity,
29   * with entries discarded using a LRU policy to keep the size of the HashMap
30   * within that bound. 
31   * 
32   * @author pugh
33   */
34  public class MapCache<K,V> extends LinkedHashMap  <K,V> {
35      private static final long serialVersionUID = 0L;
36      int maxCapacity;
37      /**
38       * Create a new MapCache
39       * @param maxCapacity - maximum number of entries in the map
40       */
41      public MapCache(int maxCapacity) {
42          super(16, 0.75f, true);
43          this.maxCapacity = maxCapacity;
44          count = new int[maxCapacity];
45      }
46      int [] count;
47      @Override  
48      public V get(Object   k) { 
49          if (false) {
50          int age = count.length-1;
51          for(Map.Entry  <K,V> e : entrySet()) {
52              if (e.getKey().equals(k)) {
53                  count[age]++;
54                  if (false && age > 20 && k instanceof JavaClass) {
55                      
56                      System.out.println("Reusing value from " + age + " steps ago ");
57                      System.out.println("Class " + ((JavaClass)k).getClassName());
58                      new RuntimeException  ().printStackTrace(System.out);
59                  }
60                  break;
61              }
62              age--;
63              
64          }
65          }
66          return super.get(k);
67      }
68      @Override  
69      protected boolean removeEldestEntry(Map.Entry  <K,V> eldest) {
70          boolean result = size() > maxCapacity;
71          if (false && result && eldest.getKey() instanceof JavaClass)
72                  System.out.println("Dropping " + ((JavaClass)eldest.getKey()).getClassName());
73          return result;
74       }
75      
76      public String   getStatistics() {
77          StringBuffer   b = new StringBuffer  ();
78          for(int c : count) 
79              b.append(c).append(" ");
80          return b.toString();
81      }
82  
83  }
84
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