Slide 1TopicsExampleVariable-Size CollectionVariable-Size CollectionVariable-Size CollectionMonolithic Programs Using Variable Sized collectionSpecial TypeSupporting EncapsulationSupporting EncapsulationHistoryImplementing A HistoryUsing a HistoryPrinting a HistoryHistoryDatabaseDatabaseremoveElement(String element)removeElement(String element)Multi-Element WindowMulti-Element WindowindexOf(String element)indexOf(String element)public boolean member(String element)public void clear()public void clear()addElement(“Mary Doe”);APointHistoryConventions for Variable-Sized CollectionConventions for Variable-Sized CollectionAlternative Conventions for Variable-Sized CollectionRead vs. Write MethodsJava Vectors, Array Lists and IteratorsCOMP 401ARRAYSInstructor: Prasun Dewan2TOPICSVariable-sized collectionsEncapsulated arrays3EXAMPLE4VARIABLE-SIZE COLLECTIONfilled partunfilled partcurrent sizemaximum size53James DeanJoe DoeJane Smithsize arrayVARIABLE-SIZE COLLECTIONfilled partunfilled partcurrent sizemaximum size6VARIABLE-SIZE COLLECTIONpublic class <ClassNeedingVariableSizeCollection> { …final static int A_MAX_SIZE = 50;String[] a = new String[A_MAX_SIZE];int aSize = 0;…//process afor (int index = 0; index < aSize; index++) System.out.println(a[index]);…final int B_MAX_SIZE = 50;String[] b = new String[B_MAX_SIZE];int bSize = 0;… //process b …}7MONOLITHIC PROGRAMS USING VARIABLE SIZED COLLECTIONVariable-sized collection takes programmer effort.Max size constant.Current size.Checking of max size.Manipulation of size.Deleting, replacing, searching takes more effort.Main program declares and uses (array-based implementation of) variable-sized collectionCannot reuse variable-size collection implementation.It is ok if program uses array as fixed-sized collection as no programmer effort required to implement it.8SPECIAL TYPEpublic class <ClassNeedingVariableSizeCollection> { ... AVariableSizeCollection a = new AVariableSizeCollection(); ... for (int index = 0; index < a.size; index++) System.out.println(a.contents[index]); … AVariableSizeCollection b = new AVariableSizeCollection(); ...}public class AVariableSizeCollection {public static final int MAX_SIZE = 50;public String[] contents = new String [MAX_SIZE];public int size = 0;}No EncapsulationSize Not Updateda.contents[a.size] = java.io.console.readLine();9SUPPORTING ENCAPSULATIONpublic interface StringHistory {public static final int MAX_SIZE = 50;public void addElement(String element);public void print();}User-specific Implementation-specific10SUPPORTING ENCAPSULATIONpublic interface StringHistory {public void addElement(String element);public String[] getStringArray();public int getSize();}Size is not a logical component of the arrayImplementation-specific (may use Vector, ArrayList or LinkedList)Can change arbitrary elements in array.11HISTORYpublic interface StringHistory {public void addElement(String element);public int size();public String elementAt(int index);}12IMPLEMENTING A HISTORYpublic class AStringHistory implements StringHistory { public final int MAX_SIZE = 50; String[] contents = new String[MAX_SIZE]; int size = 0; public int size() { return size;} public String elementAt (int index) { return contents[index]; } boolean isFull() { return size == MAX_SIZE; } public void addElement(String element) { if (isFull()) System.out.println("Adding item to a full history"); else { contents[size] = element; size++;} } }13USING A HISTORYpublic static void main(String[] args) { StringHistory names = new AStringHistory(); while (true) { String input = System.io.console.readLine(); if (input.length() > 0) if (input.charAt(0) == 'q') break; else if (input.charAt(0) == 'p' ) print(names); else names.addElement(input); }}14PRINTING A HISTORYstatic void print(StringHistory strings) { System.out.println("******************"); for ( int elementNum = 0; elementNum < strings.size(); elementNum++) System.out.println(strings.elementAt(elementNum)); System.out.println("******************");}15HISTORY16DATABASE17DATABASEpublic interface StringDatabase {//from historypublic int size();public void addElement(String element);public String elementAt(int index); //additional methods public void removeElement(String element); public void member(String element); public void clear();}18REMOVEELEMENT(STRING ELEMENT)James DeanJoe DoeJane SmithJohn Smitharraysize4removeElement(“Joe Doe”);John Smith3public void removeElement (String element) { contents[indexOf(element)] = contents[size - 1]; size--;}Elements out of order!19REMOVEELEMENT(STRING ELEMENT)James DeanJoe DoeJane Smitharraysize4removeElement(“Joe Doe”);John Smith1indexpublic void removeElement(String element) { shiftUp(indexOf(element));}20MULTI-ELEMENT WINDOWJames DeanJoe DoeJane Smitharraysize4removeElement(“Joe Doe”);John Smith1indexpublic void removeElement(String element) { shiftUp(indexOf(element));}Jane Smithcontents[index] = contents[index + 1];21John SmithMULTI-ELEMENT WINDOWJames DeanJane SmithJane SmithJohn Smitharraysize4removeElement(“Joe Doe”);2indexpublic void removeElement(String element) { shiftUp(indexOf(element));}Jane Smithvoid shiftUp(int startIndex) { for (int index = startIndex; index + 1 < size; index++) contents[index] = contents[index + 1]; size--;}3John Smith22INDEXOF(STRING ELEMENT)James DeanJoe DoeJane SmitharraysizeindexOf(“James Dean”);0index Jane Smith4John Smith23INDEXOF(STRING ELEMENT)James DeanJoe DoeJane SmitharraysizeindexOf(“Joe Doe”);0index Jane Smith4John Smithpublic int indexOf (String element) { int index; for (index = 0; index < size && !element.equals(contents[index]; index++); return index;124PUBLIC BOOLEAN MEMBER(STRING ELEMENT)James DeanJoe DoeJane Smitharraysizemember(“Joe Doe”);1index Jane Smith4John Smithpublic int indexOf (String element) { int index; for (index = 0; index < size && !element.equals(contents[index]; index++); return index;public boolean member (String element) {}return indexOf (element) < size;25PUBLIC VOID CLEAR()James DeanJoe DoeJane SmitharraysizeJane Smith4John Smithclear();public void clear() { while (size > 0) deleteElement(size -1);}321026PUBLIC VOID CLEAR()James DeanJoe DoeJane SmitharraysizeJane Smith4John Smithclear();public void clear() { size = 0;}027ADDELEMENT(“MARY DOE”);James DeanJoe