1 /**
2 * Copyright (c) 2011, University of Konstanz, Distributed Systems Group
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 * * Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * * Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * * Neither the name of the University of Konstanz nor the
13 * names of its contributors may be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
20 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
22 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
23 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
25 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 package org.treetank.service.xml.xpath.axis;
29
30 import java.util.HashSet;
31 import java.util.Set;
32
33 import org.treetank.api.INodeReadTrx;
34 import org.treetank.axis.AbsAxis;
35 import org.treetank.service.xml.xpath.XPathError;
36 import org.treetank.service.xml.xpath.XPathError.ErrorType;
37
38 /**
39 * <h1>ExceptAxis</h1>
40 * <p>
41 * Returns the nodes of the first operand except those of the second operand. This axis takes two node
42 * sequences as operands and returns a sequence containing all the nodes that occur in the first, but not in
43 * the second operand.
44 * </p>
45 */
46 public class ExceptAxis extends AbsAxis {
47
48 /** First operand sequence. */
49 private final AbsAxis mOp1;
50
51 /** Second operand sequence. */
52 private final AbsAxis mOp2;
53
54 /**
55 * Set that is used to determine, whether an item of the first operand is
56 * also contained in the result set of the second operand.
57 */
58 private final Set<Long> mDupSet;
59
60 /**
61 * Constructor. Initializes the internal state.
62 *
63 * @param rtx
64 * Exclusive (immutable) trx to iterate with.
65 * @param mOperand1
66 * First operand
67 * @param mOperand2
68 * Second operand
69 */
70 public ExceptAxis(final INodeReadTrx rtx, final AbsAxis mOperand1, final AbsAxis mOperand2) {
71
72 super(rtx);
73 mOp1 = mOperand1;
74 mOp2 = mOperand2;
75 mDupSet = new HashSet<Long>();
76
77 }
78
79 /**
80 * {@inheritDoc}
81 */
82 @Override
83 public void reset(final long mNodeKey) {
84
85 super.reset(mNodeKey);
86 if (mDupSet != null) {
87 mDupSet.clear();
88 }
89
90 if (mOp1 != null) {
91 mOp1.reset(mNodeKey);
92 }
93 if (mOp2 != null) {
94 mOp2.reset(mNodeKey);
95 }
96 }
97
98 /**
99 * {@inheritDoc}
100 */
101 @Override
102 public boolean hasNext() {
103
104 // first all items of the second operand are stored in the set.
105 while (mOp2.hasNext()) {
106 if (getNode().getDataKey() < 0) { // only nodes are
107 // allowed
108 throw new XPathError(ErrorType.XPTY0004);
109 }
110 mDupSet.add(getNode().getDataKey());
111 }
112
113 while (mOp1.hasNext()) {
114 if (getNode().getDataKey() < 0) { // only nodes are
115 // allowed
116 throw new XPathError(ErrorType.XPTY0004);
117 }
118
119 // return true, if node is not already in the set, which means, that
120 // it is
121 // not also an item of the result set of the second operand
122 // sequence.
123 if (mDupSet.add(getNode().getDataKey())) {
124 return true;
125 }
126 }
127
128 return false;
129 }
130
131 }