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comparison src/org/dancres/struct/LinkedInstances.java @ 0:3dc0c5604566

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Initial checkin of blitz 2.0 fcs - no installer yet.
author Dan Creswell <dan.creswell@gmail.com>
date Sat, 21 Mar 2009 11:00:06 +0000
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-1:000000000000 0:3dc0c5604566
1 package org.dancres.struct;
2
3 import java.io.Serializable;
4 import java.util.List;
5 import java.util.ArrayList;
6
7 /**
8 In most general situations one might store a number of instances in a
9 java.util.LinkedList or similar but this has an overhead as we create
10 a holder object for each instance we add - i.e. we're delegating the
11 management of being in the list to this holder object. This has two
12 disadvantages:
13
14 <OL>
15 <LI> Memory overhead - we have two objects per object we wish to hold. </LI>
16 <LI> Lack of direct addressability - having obtained a reference to an
17 object we might like to use that directly to access members of the list.
18 </LI>
19 </OL>
20
21 User is expected to provide suitable multi-threaded protection.
22 */
23 public class LinkedInstances implements Serializable {
24 private LinkedInstance theHead;
25 private LinkedInstance theTail;
26
27 private int theTotalInstances = 0;
28
29 public LinkedInstances() {
30 }
31
32 public LinkedInstance getHead() {
33 return theHead;
34 }
35
36 public LinkedInstance getTail() {
37 return theTail;
38 }
39
40 public List copy() {
41 ArrayList myMembers = new ArrayList();
42
43 LinkedInstance myInstance = theHead;
44 while (myInstance != null) {
45 myMembers.add(myInstance);
46
47 myInstance = myInstance.getNext();
48 }
49
50 return myMembers;
51 }
52
53 public void insert(LinkedInstance aLink) {
54 aLink.setNext(null);
55 aLink.setPrev(null);
56
57 if (theHead == null) {
58 theHead = theTail = aLink;
59 } else {
60 theHead.setPrev(aLink);
61 aLink.setNext(theHead);
62 theHead = aLink;
63 }
64
65 ++theTotalInstances;
66 }
67
68 public void add(LinkedInstance aLink) {
69 aLink.setNext(null);
70 aLink.setPrev(null);
71
72 if (theHead == null) {
73 theHead = theTail = aLink;
74 } else {
75 theTail.setNext(aLink);
76 aLink.setPrev(theTail);
77 theTail = aLink;
78 }
79
80 ++theTotalInstances;
81 }
82
83 public void remove(LinkedInstance aLink) {
84 LinkedInstance myPrev = aLink.getPrev();
85 LinkedInstance myNext = aLink.getNext();
86
87 if (myPrev != null)
88 myPrev.setNext(myNext);
89 else
90 theHead = myNext;
91
92 if (myNext != null)
93 myNext.setPrev(myPrev);
94 else
95 theTail = myPrev;
96
97 --theTotalInstances;
98
99 aLink.setPrev(null);
100 aLink.setNext(null);
101 }
102
103 public LinkedInstance removeLast() {
104 LinkedInstance myLast = theTail;
105 theTail = myLast.getPrev();
106
107 if (theTail != null)
108 theTail.setNext(null);
109 else
110 theHead = null;
111
112 myLast.setPrev(null);
113 myLast.setNext(null);
114
115 --theTotalInstances;
116
117 return myLast;
118 }
119
120 public int getSize() {
121 return theTotalInstances;
122 }
123 }