blob: bd660b1d3cac8fd6304819ac9cbcc8d2ecf7fb34 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
|
/*
* Copyright 2006-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.amazon.carbonado.cursor;
import java.util.Comparator;
import java.util.NoSuchElementException;
import com.amazon.carbonado.FetchException;
import com.amazon.carbonado.Cursor;
/**
* Wraps two Cursors and performs an <i>asymmetric set difference</i>
* operation.
*
* <p>Both cursors must return results in the same order. Ordering is preserved
* by the difference.
*
* @author Brian S O'Neill
* @see UnionCursor
* @see IntersectionCursor
* @see SymmetricDifferenceCursor
*/
public class DifferenceCursor<S> extends AbstractCursor<S> {
private final Cursor<S> mLeftCursor;
private final Cursor<S> mRightCursor;
private final Comparator<S> mOrder;
private S mNext;
private S mNextRight;
/**
* @param left cursor to wrap
* @param right cursor to wrap whose results are completely discarded
* @param order describes sort ordering of wrapped cursors, which must be
* a total ordering
*/
public DifferenceCursor(Cursor<S> left, Cursor<S> right, Comparator<S> order) {
if (left == null || right == null || order == null) {
throw new IllegalArgumentException();
}
mLeftCursor = left;
mRightCursor = right;
mOrder = order;
}
public void close() throws FetchException {
mLeftCursor.close();
mRightCursor.close();
mNext = null;
mNextRight = null;
}
public boolean hasNext() throws FetchException {
if (mNext != null) {
return true;
}
S nextLeft;
try {
while (true) {
if (mLeftCursor.hasNext()) {
nextLeft = mLeftCursor.next();
} else {
close();
return false;
}
if (mNextRight == null) {
if (mRightCursor.hasNext()) {
mNextRight = mRightCursor.next();
} else {
mNext = nextLeft;
return true;
}
}
while (true) {
int result = mOrder.compare(nextLeft, mNextRight);
if (result < 0) {
mNext = nextLeft;
return true;
} else if (result > 0) {
if (mRightCursor.hasNext()) {
mNextRight = mRightCursor.next();
} else {
mNextRight = null;
mNext = nextLeft;
return true;
}
} else {
break;
}
}
}
} catch (NoSuchElementException e) {
return false;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
public S next() throws FetchException {
try {
if (hasNext()) {
S next = mNext;
mNext = null;
return next;
}
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
throw new NoSuchElementException();
}
}
|
