Mercurial > hg > blitz_stable

annotate src/org/dancres/struct/LinkedInstances.java @ 27:511648fa4d64 Version 2.1

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Version to 2.1
author Dan Creswell <dan.creswell@gmail.com>
date Mon, 04 Jan 2010 13:00:40 +0000
parents 3dc0c5604566
children
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1 package org.dancres.struct;
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2
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3 import java.io.Serializable;
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4 import java.util.List;
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5 import java.util.ArrayList;
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6
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7 /**
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8 In most general situations one might store a number of instances in a
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9 java.util.LinkedList or similar but this has an overhead as we create
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10 a holder object for each instance we add - i.e. we're delegating the
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11 management of being in the list to this holder object. This has two
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12 disadvantages:
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13
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14 <OL>
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15 <LI> Memory overhead - we have two objects per object we wish to hold. </LI>
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16 <LI> Lack of direct addressability - having obtained a reference to an
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17 object we might like to use that directly to access members of the list.
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18 </LI>
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19 </OL>
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20
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21 User is expected to provide suitable multi-threaded protection.
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22 */
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23 public class LinkedInstances implements Serializable {
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24 private LinkedInstance theHead;
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25 private LinkedInstance theTail;
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26
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27 private int theTotalInstances = 0;
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28
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29 public LinkedInstances() {
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30 }
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31
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32 public LinkedInstance getHead() {
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33 return theHead;
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34 }
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35
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36 public LinkedInstance getTail() {
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37 return theTail;
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38 }
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39
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40 public List copy() {
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41 ArrayList myMembers = new ArrayList();
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42
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43 LinkedInstance myInstance = theHead;
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44 while (myInstance != null) {
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45 myMembers.add(myInstance);
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46
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47 myInstance = myInstance.getNext();
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48 }
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49
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50 return myMembers;
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51 }
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52
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53 public void insert(LinkedInstance aLink) {
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54 aLink.setNext(null);
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55 aLink.setPrev(null);
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56
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57 if (theHead == null) {
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58 theHead = theTail = aLink;
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59 } else {
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60 theHead.setPrev(aLink);
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61 aLink.setNext(theHead);
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62 theHead = aLink;
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63 }
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64
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65 ++theTotalInstances;
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66 }
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67
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68 public void add(LinkedInstance aLink) {
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69 aLink.setNext(null);
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70 aLink.setPrev(null);
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71
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72 if (theHead == null) {
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73 theHead = theTail = aLink;
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74 } else {
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75 theTail.setNext(aLink);
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76 aLink.setPrev(theTail);
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77 theTail = aLink;
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78 }
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79
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80 ++theTotalInstances;
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81 }
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82
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83 public void remove(LinkedInstance aLink) {
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84 LinkedInstance myPrev = aLink.getPrev();
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85 LinkedInstance myNext = aLink.getNext();
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86
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87 if (myPrev != null)
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88 myPrev.setNext(myNext);
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89 else
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90 theHead = myNext;
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91
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92 if (myNext != null)
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93 myNext.setPrev(myPrev);
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94 else
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95 theTail = myPrev;
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96
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97 --theTotalInstances;
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98
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99 aLink.setPrev(null);
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100 aLink.setNext(null);
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101 }
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102
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103 public LinkedInstance removeLast() {
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104 LinkedInstance myLast = theTail;
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105 theTail = myLast.getPrev();
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106
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107 if (theTail != null)
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108 theTail.setNext(null);
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109 else
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110 theHead = null;
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111
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112 myLast.setPrev(null);
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113 myLast.setNext(null);
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114
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115 --theTotalInstances;
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116
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117 return myLast;
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118 }
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119
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120 public int getSize() {
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121 return theTotalInstances;
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122 }
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123 }