ECM1406:DataStructuresandTeamProject. ArrayBasedLists. Chapter 3

Transcription

1 ECM1406:DataStructuresandTeamProject ArrayBasedLists Chapter 3 Array Based Lists 1/17 TheList Lists A collection of elements of the same type Length of list is number of elements in list Operations Create the list: initialize to an empty state Determine whether the list is empty Determine whether the list is full Find the size of the list Destroy (clear) the list Determine whether an item is the same as a given list element Insert an item in the list at the specified location Remove an item from the list at the specified location Replace an item at the specified location with another item Retrieve an item from the list at the specified location Search the list for a given item Lists Array Based Lists 2/17 TypeofListElements DataElement class Object directly or indirectly becomes a superclass of every Java class, user defined or built in. Reference variable of Object type can refer to any object of any class. class DataElement, superclass of every class specifying data type of list elements. Abstract methods of class DataElement: equals, compareto, makecopy and getcopy. Three concrete subclasses: IntElement when list of integers is required. DoubleElement when list of decimal numbers is required. StringElement when list of strings is required. Lists / Elements Array Based Lists 3/17

2 DataElementUML DataElement + equals(dataelement): boolean + compareto(dataelement): int + makecopy(dataelement): void + getcopy(): DataElement IntElement # num: int + IntElement() + IntElement(int) + IntElement(IntElement) + setnum(int): void + getnum(): int + equals(dataelement): boolean + compareto(dataelement): int + getcopy(): DataElement + tostring(): String StringElement # str: String + StringElement() + StringElement(String) + StringElement(StringElement) + setstring(string): void + getstring(): String + equals(dataelement): boolean + compareto(dataelement): int + getcopy(): DataElement + tostring(): String Lists / UML Array Based Lists 4/17 class ArrayListClass(1/8) An abstract class Superclass of the classes that implement a list Has three instance variables length Number of elements currently in the list m axsize Maximum number of elements that can be processed by the list list An array of reference variables ArrayListClass # length: int # maxsize: int # list: DataElement[] + ArrayListClass() + ArrayListClass(int) + ArrayListClass(ArrayListClass) + isempty(): boolean + isfull(): boolean + listsize(): int + maxlistsize(): int + print(): void + isitematequal(int, DataElement): boolean + insertat(int, DataElement): void + insertend(dataelement): void + removeat(int): void + retrieveat(int): DataElement + replaceat(int, DataElement): void + clearlist(): void + seqsearch(dataelement): int + insert(dataelement): void + remove(dataelement): void + copylist(arraylistclass): void ArryListClass Array Based Lists 5/17 Class ArrayListClass(2/8) public abstract class ArrayListClass { protected int length; protected int maxsize; protected DataElement[] list; Constructors Default Constructor Parametrised Constructor Copy Constructor General List Functions Test List Insert item into List Replace item in List Remove item from List Retrieve an item from List Copy List Abstract Functions A bstract Functions public abstract int seqsearch(dataelement searchitem); public abstract void insert(dataelement insertitem); public abstract void remove(dataelement removeitem); ArryListClass / Definition Array Based Lists 6/17

3 Class ArrayListClass(3/8) D efault Constructor public ArrayListClass() { maxsize = 100; length = 0; list = new DataElement[maxSize]; // end Default Constructor Param etrised Constructor public ArrayListClass(int size) { if (size <= 0) { maxsize = 100; else { maxsize = size; length = 0; list = new DataElement[maxSize]; // end Parametrised Constructor ArryListClass / Constructors Array Based Lists 7/17 Class ArrayListClass(4/8) Copy Constructor public ArrayListClass(ArrayListClass otherlist) { maxsize = otherlist.maxsize; length = otherlist.length; list = new DataElement[maxSize]; // create the array for (int j = 0; j < length; j++) { // copy otherlist list[j] = otherlist.list[j].getcopy(); // end Copy Constructor Copy List public void copylist(arraylistclass otherlist) { if (this!= otherlist) { // avoid self-assignment clearlist(); // Destroy the old list ArrayListClass(otherList); // end copylist // Make a copy of the new list ArryListClass / Copy Array Based Lists 8/17 Class ArrayListClass(5/8) Test List public boolean isempty() { return (length == 0); // end isempty public boolean isfull() { return (length == maxsize); // end isfull public void clearlist() { for (int i = 0; i < length; i++) { list[i] = null; length = 0; System.gc(); // end clearlist public int listsize() { return length; // end listsize public int maxlistsize() { return maxsize; // end maxlistsize public void print() { for (int i = 0; i < length; i++) { System.out.print( list[i] + " "); System.out.println(); // end print public boolean isitematequal(int location, DataElement item) { return list[location].equals(item); // end isitematequal ArryListClass / Tests Array Based Lists 9/17

4 Class ArrayListClass(6/8) Insert item into List public void insertat(int location, DataElement insertitem) { if (location < 0 location >= maxsize) { else { if (length >= maxsize) { // list is full System.err.println("Cannot insert in a full list."); else { for (int i = length; i > location; i--) { list[i] = list[i - 1]; // move the elements down // insert the item at the specified position list[location] = insertitem.getcopy(); length++; // increment the length // end insertat Report invalid location error System.err.println("The location of the item to be replaced " + "is out of range."); ArryListClass / Insert At Array Based Lists 10/17 Class ArrayListClass(7/8) Insert item into List(Continued) public void insertend(dataelement insertitem) { if (length >= maxsize) { // the list is full System.err.println("Cannot insert in a full list."); else { // insert the item at the end list[length] = insertitem.getcopy(); length++; // end insertend Replace item in List public void replaceat(int location, DataElement item) { if (location < 0 location >= length) { else { list[location].makecopy(item); // end replaceat ArryListClass / Insert and Replace Array Based Lists 11/17 Class ArrayListClass(8/8) RemoveitemfromList public void removeat(int location) { if (location < 0 location >= length) { else { for (int i = location; i < length - 1; i++) { list[i] = list[i+1]; list[length - 1] = null; length--; // end removeat Retrieve an item from List public DataElement retrieveat(int location) { if (location < 0 location >= length) { return null; else { return list[location].getcopy(); // end retrieveat ArryListClass / Retrieve and Remove Array Based Lists 12/17

5 U nordered List class UnorderedArrayList is a subclass of the class ArrayListClass Elements are not necessarily sorted class UnorderedList implements operations search, insert and remove. ArrayListClass UnorderedArrayList + UnorderedArrayList() + UnorderedArrayList(int) + UnorderedArrayList(UnorderedArrayList) + seqsearch(dataelement): void + insert(dataelement): void + remove(dataelement): void Unordered List Array Based Lists 13/17 Class UnorderedArrayList public class UnorderedArrayList extends ArrayListClass { Constructors Concrete Implementations of Abstract Methods Search Insert Remove Constructors public UnorderedArrayList() { super(); // end default constructor public UnorderedArrayList(int size) { super(size); // end parametrised constructor public UnorderedArrayList(UnorderedArrayList otherlist) { super(otherlist); // end copy constructor Unordered List / Definition Array Based Lists 14/17 U norderedlist: Search Search of a searchitem in the current list. Returns the location of the item in the list if it is found, or -1 if searchitem is not in the list. public int seqsearch(dataelement searchitem) { int loc; boolean found = false; for (loc = 0; loc < length; loc++) { if (list[loc].equals(searchitem)) { found = true; break; // We can stop looking now if (found) { return loc; else { return -1; // end seqsearch Unordered List / Search Array Based Lists 15/17

6 U norderedlist: Insert Inserts a new item (insertitem) in the list. Uses method seqsearch to determine whether insertitem is already in list. public void insert(dataelement insertitem) { int loc; if (length == 0) { // list is empty - insert item into list list[length++] = insertitem.getcopy(); else { if (length == maxsize) { System.err.println("Cannot insert in a full list."); else { // list has space for new item loc = seqsearch(insertitem); if (loc == -1) { // item not already in the list list[length++] = insertitem.getcopy(); else { System.err.println("The item to be inserted is already in " + "the list. No duplicates are allowed."); // end if length == maxsize // end if length == 0 // end insert Unordered List / Insert Array Based Lists 16/17 U norderedlist: Rem ove Removes an item from the list. Uses the methods seqsearch and removeat to remove an item from the list. public void remove(dataelement removeitem) { int loc; if (length == 0) { System.err.println("Cannot delete from an empty list."); else { loc = seqsearch(removeitem); // Find the item if (loc!= -1) { removeat(loc); // Remove it else { System.out.println("The item to be deleted is " + "not in the list."); // end remove Unordered List / Remove Array Based Lists 17/17