CircularIdentityList


1   /*
2    * @(#)CircularIdentityList.java    1.5 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   package com.sun.java.swing.plaf.gtk;
8   
9   import java.util.*;
10  
11  /**
12   * An circular linked list like data structure that uses identity for equality
13   * testing.
14   *
15   * @version 1.5, 12/19/03
16   * @author Scott Violet
17   */
18  class CircularIdentityList implements Cloneable   {
19      private Property property;
20  
21      /**
22       * Sets a particular value.
23       */
24      public synchronized void set(Object   key, Object   value) {
25          if (property == null) {
26              property = new Property(key, value, null);
27          }
28          else {
29              Property p = property;
30              Property last = p;
31  
32              do {
33                  if (p.key == key) {
34                      p.value = value;
35                      property = p;
36                      return;
37                  }
38                  last = p;
39                  p = p.next;
40              } while (p != property && p != null);
41              // not defined
42              if (value != null) {
43                  if (p == null) {
44                      // Only one element
45                      p = property;
46                  }
47                  property = new Property(key, value, p);
48                  last.next = property;
49              }
50          }
51      }
52  
53      /**
54       * Returns the value currently being referenced.
55       */
56      public synchronized Object   get() {
57          if (property == null) {
58              return null;
59          }
60          return property.value;
61      }
62  
63      /**
64       * Returns the value for a specific key.
65       */
66      public synchronized Object   get(Object   key) {
67          if (property == null) {
68              return null;
69          }
70          Property p = property;
71  
72          do {
73              if (p.key == key) {
74                  return p.value;
75              }
76              p = p.next;
77          } while (p != property && p != null);
78          return null;
79      }
80  
81      /**
82       * Advanced the list returning the next key. This will only return
83       * null if the list is empty.
84       */
85      public synchronized Object   next() {
86          if (property == null) {
87              return null;
88          }
89          if (property.next == null) {
90              return property.key;
91          }
92          property = property.next;
93          return property.key;
94      }
95  
96      public synchronized Object   clone() {
97          try {
98              CircularIdentityList list = (CircularIdentityList)super.clone();
99  
100             if (property != null) {
101                 list.property = (Property)property.clone();
102 
103                 Property last = list.property;
104 
105                 while (last.next != null && last.next != property) {
106                     last.next = (Property)last.next.clone();
107                     last = last.next;
108                 }
109                 last.next = list.property;
110             }
111             return list;
112         } catch (CloneNotSupportedException   cnse) {
113         }
114         return null;
115     }
116 
117 
118     static class Property implements Cloneable   {
119         Object   key;
120         Object   value;
121         Property next;
122 
123         Property(Object   key, Object   value, Property next) {
124             this.key = key;
125             this.value = value;
126             this.next = next;
127         }
128 
129         public Object   clone() {
130             try {
131                 return super.clone();
132             } catch (CloneNotSupportedException   cnse) {
133             }
134             return null;
135         }
136     }
137 }
138
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