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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
|
/*******************************************************************************
* Copyright (c) 2005, 2010 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0, which accompanies this distribution
* and is available at http://www.eclipse.org/legal/epl-v10.html.
*
* Contributors:
* Oracle - initial API and implementation
******************************************************************************/
package org.eclipse.jpt.utility.internal.iterators;
import java.util.Collection;
import java.util.Iterator;
import org.eclipse.jpt.utility.internal.StringTools;
/**
* A <code>CloneIterator</code> iterates over a copy of a collection,
* allowing for concurrent access to the original collection.
* <p>
* The original collection passed to the <code>CloneIterator</code>'s
* constructor should be synchronized (e.g. {@link java.util.Vector});
* otherwise you run the risk of a corrupted collection.
* <p>
* By default, a <code>CloneIterator</code> does not support the
* {@link #remove()} operation; this is because it does not have
* access to the original collection. But if the <code>CloneIterator</code>
* is supplied with an {@link Remover} it will delegate the
* {@link #remove()} operation to the {@link Remover}.
* Alternatively, a subclass can override the {@link #remove(Object)}
* method.
*
* @param <E> the type of elements returned by the iterator
*
* @see org.eclipse.jpt.utility.internal.iterables.LiveCloneIterable
* @see org.eclipse.jpt.utility.internal.iterables.SnapshotCloneIterable
*/
public class CloneIterator<E>
implements Iterator<E>
{
private final Iterator<Object> iterator;
private E current;
private final Remover<E> remover;
private boolean removeAllowed;
// ********** constructors **********
/**
* Construct an iterator on a copy of the specified collection.
* The {@link #remove()} method will not be supported,
* unless a subclass overrides the {@link #remove(Object)}.
*/
public CloneIterator(Collection<? extends E> collection) {
this(collection, Remover.ReadOnly.<E>instance());
}
/**
* Construct an iterator on a copy of the specified array.
* The {@link #remove()} method will not be supported,
* unless a subclass overrides the {@link #remove(Object)}.
*/
public CloneIterator(E[] array) {
this(array, Remover.ReadOnly.<E>instance());
}
/**
* Construct an iterator on a copy of the specified collection.
* Use the specified remover to remove objects from the
* original collection.
*/
public CloneIterator(Collection<? extends E> collection, Remover<E> remover) {
this(remover, collection.toArray());
}
/**
* Construct an iterator on a copy of the specified array.
* Use the specified remover to remove objects from the
* original array.
*/
public CloneIterator(E[] array, Remover<E> remover) {
this(remover, array.clone());
}
/**
* Internal constructor used by subclasses.
* Swap order of arguments to prevent collision with other constructor.
* The passed in array will *not* be cloned.
*/
protected CloneIterator(Remover<E> remover, Object... array) {
super();
this.iterator = new ArrayIterator<Object>(array);
this.current = null;
this.remover = remover;
this.removeAllowed = false;
}
// ********** Iterator implementation **********
public boolean hasNext() {
return this.iterator.hasNext();
}
public E next() {
this.current = this.nestedNext();
this.removeAllowed = true;
return this.current;
}
public void remove() {
if ( ! this.removeAllowed) {
throw new IllegalStateException();
}
this.remove(this.current);
this.removeAllowed = false;
}
// ********** internal methods **********
/**
* The collection passed in during construction held elements of type <code>E</code>,
* so this cast is not a problem. We need this cast because
* all the elements of the original collection were copied into
* an object array (<code>Object[]</code>).
*/
@SuppressWarnings("unchecked")
protected E nestedNext() {
return (E) this.iterator.next();
}
/**
* Remove the specified element from the original collection.
* <p>
* This method can be overridden by a subclass as an
* alternative to building a {@link Remover}.
*/
protected void remove(E e) {
this.remover.remove(e);
}
@Override
public String toString() {
return StringTools.buildToStringFor(this);
}
//********** member interface **********
/**
* Used by {@link CloneIterator} to remove
* elements from the original collection; since the iterator
* does not have direct access to the original collection.
*/
public interface Remover<T> {
/**
* Remove the specified object from the original collection.
*/
void remove(T element);
final class ReadOnly<S> implements Remover<S> {
@SuppressWarnings("rawtypes")
public static final Remover INSTANCE = new ReadOnly();
@SuppressWarnings("unchecked")
public static <R> Remover<R> instance() {
return INSTANCE;
}
// ensure single instance
private ReadOnly() {
super();
}
// remove is not supported
public void remove(Object element) {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return "CloneIterator.Remover.ReadOnly"; //$NON-NLS-1$
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
}
}
|
