1 /*
2 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
3 */
4 /*
5 * Licensed to the Apache Software Foundation (ASF) under one or more
6 * contributor license agreements. See the NOTICE file distributed with
7 * this work for additional information regarding copyright ownership.
8 * The ASF licenses this file to You under the Apache License, Version 2.0
9 * (the "License"); you may not use this file except in compliance with
10 * the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing, software
15 * distributed under the License is distributed on an "AS IS" BASIS,
16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17 * See the License for the specific language governing permissions and
18 * limitations under the License.
19 */
20
21 package com.sun.org.apache.xml.internal.dtm.ref;
22
23 import com.sun.org.apache.xml.internal.utils.IntVector;
24 import java.util.ArrayList;
25 import java.util.List;
26
27 /** <p>DTMStringPool is an "interning" mechanism for strings. It will
28 * create a stable 1:1 mapping between a set of string values and a set of
29 * integer index values, so the integers can be used to reliably and
30 * uniquely identify (and when necessary retrieve) the strings.</p>
31 *
32 * <p>Design Priorities:
33 * <ul>
34 * <li>String-to-index lookup speed is critical.</li>
35 * <li>Index-to-String lookup speed is slightly less so.</li>
36 * <li>Threadsafety is not guaranteed at this level.
37 * Enforce that in the application if needed.</li>
38 * <li>Storage efficiency is an issue but not a huge one.
39 * It is expected that string pools won't exceed about 2000 entries.</li>
40 * </ul>
41 * </p>
42 *
43 * <p>Implementation detail: A standard Hashtable is relatively
44 * inefficient when looking up primitive int values, especially when
45 * we're already maintaining an int-to-string vector. So I'm
46 * maintaining a simple hash chain within this class.</p>
47 *
48 * <p>NOTE: There is nothing in the code that has a real dependency upon
49 * String. It would work with any object type that implements reliable
50 * .hashCode() and .equals() operations. The API enforces Strings because
51 * it's safer that way, but this could trivially be turned into a general
52 * ObjectPool if one was needed.</p>
53 *
54 * <p>Status: Passed basic test in main().</p>
55 *
56 * @LastModified: Oct 2017
57 */
58 public class DTMStringPool
59 {
60 List<String> m_intToString;
61 static final int HASHPRIME=101;
62 int[] m_hashStart=new int[HASHPRIME];
63 IntVector m_hashChain;
64 public static final int NULL=-1;
65
66 /**
67 * Create a DTMStringPool using the given chain size
68 *
69 * @param chainSize The size of the hash chain vector
70 */
71 public DTMStringPool(int chainSize)
72 {
73 m_intToString = new ArrayList<>();
74 m_hashChain= new IntVector(chainSize);
75 removeAllElements();
76
77 // -sb Add this to force empty strings to be index 0.
78 stringToIndex("");
79 }
80
81 public DTMStringPool()
82 {
83 this(512);
84 }
85
86 public void removeAllElements()
87 {
88 m_intToString.clear();
89 for(int i=0;i<HASHPRIME;++i)
90 m_hashStart[i]=NULL;
91 m_hashChain.removeAllElements();
92 }
93
94 /** @return string whose value is uniquely identified by this integer index.
95 * @throws java.lang.IndexOutOfBoundsException
96 * if index doesn't map to a string.
97 * */
98 public String indexToString(int i)
99 throws java.lang.IndexOutOfBoundsException
100 {
101 if(i==NULL) return null;
102 return m_intToString.get(i);
103 }
104
105 /** @return integer index uniquely identifying the value of this string. */
106 public int stringToIndex(String s)
107 {
108 if(s==null) return NULL;
109
110 int hashslot=s.hashCode()%HASHPRIME;
111 if(hashslot<0) hashslot=-hashslot;
112
113 // Is it one we already know?
114 int hashlast=m_hashStart[hashslot];
115 int hashcandidate=hashlast;
116 while(hashcandidate!=NULL)
117 {
118 if(m_intToString.get(hashcandidate).equals(s))
119 return hashcandidate;
120
121 hashlast=hashcandidate;
122 hashcandidate=m_hashChain.elementAt(hashcandidate);
123 }
124
125 // New value. Add to tables.
126 int newIndex=m_intToString.size();
127 m_intToString.add(s);
128
129 m_hashChain.addElement(NULL); // Initialize to no-following-same-hash
130 if(hashlast==NULL) // First for this hash
131 m_hashStart[hashslot]=newIndex;
132 else // Link from previous with same hash
133 m_hashChain.setElementAt(newIndex,hashlast);
134
135 return newIndex;
136 }
137
138 /** Command-line unit test driver. This test relies on the fact that
139 * this version of the pool assigns indices consecutively, starting
140 * from zero, as new unique strings are encountered.
141 */
142 public static void _main(String[] args)
143 {
144 String[] word={
145 "Zero","One","Two","Three","Four","Five",
146 "Six","Seven","Eight","Nine","Ten",
147 "Eleven","Twelve","Thirteen","Fourteen","Fifteen",
148 "Sixteen","Seventeen","Eighteen","Nineteen","Twenty",
149 "Twenty-One","Twenty-Two","Twenty-Three","Twenty-Four",
150 "Twenty-Five","Twenty-Six","Twenty-Seven","Twenty-Eight",
151 "Twenty-Nine","Thirty","Thirty-One","Thirty-Two",
152 "Thirty-Three","Thirty-Four","Thirty-Five","Thirty-Six",
153 "Thirty-Seven","Thirty-Eight","Thirty-Nine"};
154
155 DTMStringPool pool=new DTMStringPool();
156
157 System.out.println("If no complaints are printed below, we passed initial test.");
158
159 for(int pass=0;pass<=1;++pass)
160 {
161 int i;
162
163 for(i=0;i<word.length;++i)
164 {
165 int j=pool.stringToIndex(word[i]);
166 if(j!=i)
167 System.out.println("\tMismatch populating pool: assigned "+
168 j+" for create "+i);
169 }
170
171 for(i=0;i<word.length;++i)
172 {
173 int j=pool.stringToIndex(word[i]);
174 if(j!=i)
175 System.out.println("\tMismatch in stringToIndex: returned "+
176 j+" for lookup "+i);
177 }
178
179 for(i=0;i<word.length;++i)
180 {
181 String w=pool.indexToString(i);
182 if(!word[i].equals(w))
183 System.out.println("\tMismatch in indexToString: returned"+
184 w+" for lookup "+i);
185 }
186
187 pool.removeAllElements();
188
189 System.out.println("\nPass "+pass+" complete\n");
190 } // end pass loop
191 }
192 }