blob: 8d51996853d1946ca509db7e6736bce1294c8fc3 (
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
|
package bjc.utils.funcutils;
import java.util.*;
import java.util.function.*;
import bjc.data.ArrayIterator;
/**
* Utility methods for dealing with iterators.
*
* @author bjculkin
*
*/
public class IteratorUtils {
/**
* A chain iterator. This is essentially flatMap in iterator form.
*
* @author bjculkin
*
* @param <T1>
* The type of the input values.
*
* @param <T2>
* The type of the output values.
*/
public static class ChainIterator<T1, T2> implements Iterator<T2> {
private Iterator<T1> mainItr;
private Function<T1, Iterator<T2>> trans;
private Iterator<T2> curItr;
/**
* Create a new chain iterator.
*
* @param mainItr
* The main iterator for input.
*
* @param trans
* The transformation to use to produce the outputs.
*/
public ChainIterator(Iterator<T1> mainItr, Function<T1, Iterator<T2>> trans) {
this.mainItr = mainItr;
this.trans = trans;
}
@Override
public boolean hasNext() {
if (curItr != null) {
return curItr.hasNext() ? true : mainItr.hasNext();
}
return mainItr.hasNext();
}
@Override
public T2 next() {
if (curItr == null || !curItr.hasNext()) {
curItr = trans.apply(mainItr.next());
}
return curItr.next();
}
}
/**
* Convert an iterator to an iterable.
*
* @param itr
* The iterator to convert.
*
* @return An iterable that gives back that iterator.
*/
public static <E> Iterable<E> I(Iterator<E> itr) {
return () -> itr;
}
/**
* Convert an iterable to an iterator.
*
* @param itr
* The iterable to convert.
*
* @return The iterator from that iterable
*/
public static <E> Iterator<E> I(Iterable<E> itr) {
return itr.iterator();
}
/**
* Convert an array to an iterator.
*
* @param parms
* The array to iterate over.
*
* @return An iterator over the provided array.
*/
@SafeVarargs
public static <E> Iterator<E> AI(E... parms) {
return new ArrayIterator<>(parms);
}
/**
* Create a chain iterator.
*
* @param itrA
* The iterator for input values.
*
* @param itrB
* The transformation for output values.
*
* @return A chain iterator from the provided values.
*/
public static <A, B> Iterator<B> chain(Iterator<A> itrA,
Function<A, Iterator<B>> itrB) {
return new ChainIterator<>(itrA, itrB);
}
}
|
