blob: ea5076e854767a2943ac6aae278a014888ca1336 (
plain) (
blame)
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
|
/*******************************************************************************
* Copyright (c) 2005, 2007 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.Iterator;
import java.util.NoSuchElementException;
import org.eclipse.jpt.utility.internal.StringTools;
/**
* A <code>ChainIterator</code> provides a pluggable <code>Iterator</code>
* that loops over a chain of arbitrarily linked objects. The chain
* should be null-terminated (i.e. a call to the <code>nextLink(Object)</code>
* method should return <code>null</code> when it is passed the last
* link of the chain).
* To use, supply a starting link and supply a <code>Linker</code> or
* subclass <code>ChainIterator</code> and override the
* <code>nextLink(Object)</code> method.
* The starting link will be the first object returned by the iterator.
* If the starting link is <code>null</code>, the iterator will be empty.
* Note that the iterator does not support <code>null</code> elements.
*/
public class ChainIterator<E>
implements Iterator<E>
{
private E nextLink;
private final Linker<E> linker;
/**
* Construct an iterator with the specified starting link
* and a disabled linker.
* Use this constructor if you want to override the
* <code>nextLink(Object)</code> method instead of building
* a <code>Linker</code>.
*/
public ChainIterator(E startLink) {
this(startLink, Linker.Disabled.<E>instance());
}
/**
* Construct an iterator with the specified starting link
* and linker.
*/
public ChainIterator(E startLink, Linker<E> linker) {
super();
this.nextLink = startLink;
this.linker = linker;
}
public boolean hasNext() {
return this.nextLink != null;
}
public E next() {
if (this.nextLink == null) {
throw new NoSuchElementException();
}
E result = this.nextLink;
this.nextLink = this.nextLink(this.nextLink);
return result;
}
public void remove() {
throw new UnsupportedOperationException();
}
/**
* Return the next link in the chain.
*/
protected E nextLink(E currentLink) {
return this.linker.nextLink(currentLink);
}
@Override
public String toString() {
return StringTools.buildToStringFor(this, this.nextLink);
}
//********** inner classes **********
/**
* Used by <code>ChainIterator</code> to link
* the elements in the chain.
*/
public interface Linker<T> {
/**
* Return the next link in the chain.
*/
T nextLink(T currentLink);
final class Null<S> implements Linker<S> {
@SuppressWarnings("unchecked")
public static final Linker INSTANCE = new Null();
@SuppressWarnings("unchecked")
public static <R> Linker<R> instance() {
return INSTANCE;
}
// ensure single instance
private Null() {
super();
}
// simply return null, indicating the chain is ended
public S nextLink(S currentLink) {
return null;
}
@Override
public String toString() {
return "ChainIterator.Linker.Null";
}
}
final class Disabled<S> implements Linker<S> {
@SuppressWarnings("unchecked")
public static final Linker INSTANCE = new Disabled();
@SuppressWarnings("unchecked")
public static <R> Linker<R> instance() {
return INSTANCE;
}
// ensure single instance
private Disabled() {
super();
}
// throw an exception
public S nextLink(S currentLink) {
throw new UnsupportedOperationException(); // ChainIterator.nextLink(Object) was not implemented
}
@Override
public String toString() {
return "ChainIterator.Linker.Disabled";
}
}
}
}
|
