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Java > Open Source Codes > com > sleepycat > je > utilint > TinyHashSet


1 /*-
2  * See the file LICENSE for redistribution information.
3  *
4  * Copyright (c) 2002,2006 Oracle. All rights reserved.
5  *
6  * $Id: TinyHashSet.java,v 1.6 2006/10/30 21:14:29 bostic Exp $
7  */
8
9 package com.sleepycat.je.utilint;
10
11 import java.util.HashSet JavaDoc;
12 import java.util.Iterator JavaDoc;
13 import java.util.NoSuchElementException JavaDoc;
14 import java.util.Set JavaDoc;
15
16 /**
17  * TinyHashSet is used to optimize (for speed, not space) the case where a
18  * HashSet generally holds a single element. This saves us the cost of
19  * creating the HashSet and related elements as well as call Object.hashCode().
20  *
21  * If single != null, it's the only element in the TinyHashSet. If set != null
22  * then there are multiple elements in the TinyHashSet. It should never be
23  * true that (single != null) && (set != null).
24  */
25 public class TinyHashSet {
26
27     private Set JavaDoc set;
28     private Object JavaDoc single;
29
30     /*
31      * Will return a fuzzy value if the not under synchronized control.
32      */
33     public int size() {
34     if (single != null) {
35         return 1;
36     } else if (set != null) {
37         return set.size();
38     } else {
39         return 0;
40     }
41     }
42
43     public boolean remove(Object JavaDoc o) {
44     assert (single == null) || (set == null);
45     if (single != null) {
46         if (single == o ||
47         single.equals(o)) {
48         single = null;
49         return true;
50         } else {
51         return false;
52         }
53     } else if (set != null) {
54         return set.remove(o);
55     } else {
56         return false;
57     }
58     }
59
60     public boolean add(Object JavaDoc o) {
61     assert (single == null) || (set == null);
62     if (set != null) {
63         return set.add(o);
64     } else if (single == null) {
65         single = o;
66         return true;
67     } else {
68         set = new HashSet JavaDoc();
69         set.add(single);
70         single = null;
71         return set.add(o);
72     }
73     }
74
75     public Set JavaDoc copy() {
76     assert (single == null) || (set == null);
77     if (set != null) {
78         return new HashSet JavaDoc(set);
79     } else {
80         Set JavaDoc ret = new HashSet JavaDoc();
81         if (single != null) {
82         ret.add(single);
83         }
84         return ret;
85     }
86     }
87
88     public Iterator JavaDoc iterator() {
89     assert (single == null) || (set == null);
90     if (set != null) {
91         return set.iterator();
92     } else {
93         return new SingleElementIterator(single, this);
94     }
95     }
96
97     /*
98      * Iterator that is used to just return one element.
99      */
100     public static class SingleElementIterator implements Iterator JavaDoc {
101     Object JavaDoc theObject;
102     TinyHashSet theSet;
103     boolean returnedTheObject = false;
104
105     SingleElementIterator(Object JavaDoc o, TinyHashSet theSet) {
106         theObject = o;
107         this.theSet = theSet;
108         returnedTheObject = (o == null);
109     }
110
111     public boolean hasNext() {
112         return !returnedTheObject;
113     }
114
115     public Object JavaDoc next() {
116         if (returnedTheObject) {
117         throw new NoSuchElementException JavaDoc();
118         }
119
120         returnedTheObject = true;
121         return theObject;
122     }
123
124     public void remove() {
125         if (theObject == null ||
126         !returnedTheObject) {
127         throw new IllegalStateException JavaDoc();
128         }
129         theSet.remove(theObject);
130     }
131     }
132 }
133
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