To describe the Java Collections Framework. To use the Iterator interface to traverse a. To discover the Set interface, and know how

Transcription

1 Chapter 22 Java Collections Framework :Objectives To describe the Java Collections Framework hierarchy To use the Iterator interface to traverse a collection To discover the Set interface, and know how and when to use HashSet to store elements To explore the List interface, LinkedList and Vector to store elements To explore Map, and know how to use HashMap to store values associated with keys 1

2 Java Collection Framework hierarchyh A collection is a container object that represents a group of objects, often referred to as elements. The Java Collections Framework supports three types of collections, named sets, lists, and maps. 2

3 Java Collection Framework hierarchy, h cont. Set and List are subinterfaces of Collection. SortedSet TreeSet Set AbstractSet HashSet LinkedHashSet Collection AbstractCollection Vector Stack List AbstractList ArrayList AbstractSequentialList LinkedList Interfaces Abstract Classes Concrete Classes Slide 5 3

4 Java Collection Framework hierarchy, h cont. An instance of Map represents a group of objects, each of which is associated with a key. You can get the object from a map using a key, and you have to use a key to put the object into the map. SortedMap TreeMap Map AbstractMap HashMap LinkedHashMap Interfaces Abstract Classes Concrete Classes 4

5 The Collection Interface:Set, List «interface» java.util.collection<e> +add(o: E): boolean +addall(c: Collection<? extends E): boolean +clear(): void +contains(o: Object): boolean +containsall(c: Collection<?>):boolean l +equals(o: Object): boolean +hashcode(): int +isempty(): boolean +iterator(): Iterator +remove(o: Object): boolean +removeall(c: Collection<?>): boolean +retainall(c: Collection<?>): boolean +size(): int +toarray(): Object[] The Collection interface is the root interface for manipulating a collection of objects. Adds a new element o to this collection. Adds all the elements in the collection c to this collection. Removes all the elements from this collection. Returns true if this collection contains the element o. Returns true if this collection contains all the elements in c. Returns true if this collection is equal to another collection o. Returns the hash code for this collection. Returns true if this collection contains no elements. Returns an iterator for the elements in this collection. Removes the element o from this collection. Removes all the elements in c from this collection. Retains the elements that are both in c and in this collection. Returns the number of elements in this collection. ReturnsanarrayofObjectfortheelementsinthiscollection array for the elements this collection. «interface» java.util.iterator<e> +hasnext(): boolean +next(): E +remove(): void Returns true if this iterator has more elements to traverse. Returns the next element from this iterator. Removes the last element obtained using the next method. slide3 5

6 The Set Interface The Set interface extends the Collection interface. It does not introduce new methods or ก าหนดเง อนไข constants, but it stipulates that an instance of Set contains no duplicate elements. That is no two elements e1 and e2 can be in the set such that e1.equals(e2) equals(e2) istrue. false Class HashSet implements this interface ค าข อม ลของสมาช กไม สามารถซ าก นได และล าด บของสมาช กไม ม ความส าค ญ 6

7 The Set Interface Hierarchy «interface» java.util.set<e> java.util.abstractset<e> java.util.hashset<e> +HashSet() +HashSet(c: Collection<? extends E>) java.util.linkedhashset<e> +LinkedHashSet() +LinkedHashSet(c: Collection<? extends E>) «interface» java.util.sortedset<e> +first(): E +last(): E +headset(toelement: E): SortedSet<E> +tailset(fromelement: E): SortedSet<E> java.util.treeset<e> +TreeSet() +TreeSet(c: Collection<? extends E>) +TreeSet(c: Comparator<? super E>) Returns the first in this set. Returns the last in this set. headset/tailset returns a portion of the set less than toelement/greater than fromelement. Creates a tree set with the specified comparator. 7

8 Example: HashSet 1 import java.util.*; 2 3 public class TestHashSet { 4 public static void main(string[] args) { 5 // Create a hash set 6 Set<String> set = new HashSet<>(); 7 set.add("london"); 8 set.add("new York"); 9 set.add("san Francisco"); 10 set.add("new York"); 11 System.out.println(set); 12 System.out.println("Before remove the size is:"+ set.size()); 13 set.remove("london"); } } ผลการร น ผลการรน System.out.println("set contain London:"+ set.contains("london")); System.out.println("After remove the size is: " + set.size()); [San Francisco, New York, London] Before remove the size is: 3 set contain London: false After remove the size is: 2 8

9 Iterator Interface ภายในอ นเตอร เฟส ภายในอนเตอรเฟส Collection ม เมธอดช อ มเมธอดชอ iterator() ส งค ากล บเป น Iterator ซ งเป นอ นเตอร เฟสส าหร บอ างถ งข อม ล สมาช กประเภท สมาชกประเภท Set ม เมธอดส าค ญด งน มเมธอดสาคญดงน boolean hasnext() Object t next() void remove() 9

10 Example:iterator() 1 import java.util.*; 2 3 public class TestHashSetIterator { 4 public static ti void main(string[] i args) { set.add("new York"); // Create a hash set Set<String> set = new HashSet<>(); set.add("london"); 9 set.add("san Francisco"); 10 // Obtain an iterator for the hash set 11 Iterator iterator = set.iterator(); 12 // Display the elements in the hash set } 17 } while (iterator.hasnext()) { System.out.print(iterator.next() + ", "); } output San Francisco, New York, London, 10

11 The List Interface The List interface extends the Collection interface. To allow duplicate elements to be stored in a collection, you need to use a list. Ali list can store duplicate elements, and also allow the user to specify where the element is stored. The user can access the element by index. ArrayList, Vector and LinkedList implement this interface คาข อม ลของสมาชกซ ากนได และล าดบของสมาชกม ความส าคญ 11

12 The List Interface, cont. Collection List +add(index: int, element: Object) : boolean +addall(index: int, collection: Collection) : boolean +get(index: int) : Object +indexof(element: Object) : int +lastindexof(element: Object) : int +listiterator() : ListIterator +listiterator(startindex: int) : ListIterator +remove(index: int) : int +set(index: int, element: Object) : Object +sublist(fromindex: int, toindex: int) : List Adds a new element at the specified index Adds all elements in the collection to this list at the specified index Returns the element in this list at the specified index Returns the index of the first matching element Returns the index of the last matching element Returns the list iterator for the elements in this list Returns the iterator for the elements from startindex Removes the element at the specified index Sets the element at the specified index Returns a sublist from fromindex to toindex 12

13 LinkedList List AbstractSequentialList LinkedList +addfirst(o: Object) : void +addlast(o: Object) : void +getfirst() : Object +getlast() : Object +removefirst() : Object +removelast() : Object Adds the object to the head of this list Adds the object to the tail of this list Returns the first element from this list Returns the last element from this list Returns and removes the first element from this list Returns and removes the last element from this list 13

14 Example: LinkedList 1 import java.util.*; 2 3 public class TestList { 4 public static void main(string[] args) { 5 List<String> list = new LinkedList<>(); 6 list.add("america"); 7 list.add("canada"); 8 System.out.println("fist one: " + list.get(0)); 9 list.add(0,"russia"); 10 System.out.println("list: " + list); 11 System.out.println("Size: " + list.size()); 12 list.add("france"); 13 System.out.println("list: li " + list); 14 System.out.println("index of America is:"+list.indexof("america")); 15 } 16 } 17 output fist one: America list: [Russia, America, Canada] Size: 3 list: [Russia, America, Canada, France] index of America is:1 14

15 อ นเตอร เฟส ListIterator Iterator ListIterator +add(o: Object) : void +hasprevious() : boolean +nextindex() : int +previousindex() : int +previous() : Object +set(o: Object) : void +hasnext(): boolean +next(): E ใช อ างข อม ลสมาช กประเภท List ภายในอ นเตอร เฟส List ม เมธอดช อ listiterator() เป น เมธอดส งค ากล บเป น ListIterator Adds the specified object to the list Returns true if this list iterator has more elements when traversing backward. Returns the index of the next element Returns the index of the previosu element Returns the previous element in this list iterator Replaces the last element returned by the previous or next method with the specified element Returns true if this iterator has more elements to traverse. Returns the next element from this iterator 15

16 Example:ListIterator 1 import java.util.*; 2 public class TestListIterator { 3 public static ti void main(string[] i args) { 4 List<String> list = new LinkedList<>(); 5 list.add("america"); 6 list.add("canada"); 7 list.add("russia"); 8 list.add("france"); 9 // System.out.println("list: " + list); 10 ListIterator it = list.listiterator(); 11 while(it.hasnext()){ hasnext()){ 12 System.out.println(it.next()); 13 } 14 } 15 } output America Canada Russia France 16

17 The Vector Class, cont. List Vector +addelement(o: Object): void +capacity(): int +copyinto(anarray: Object[]): void +elementat(index: int): Object +elements(): Enumeration +ensurecapacity(): void +firstelement(): Object +insertelementat(o: Object, index: int): void +lastelement(): Object +removeallelements() : void +removeelement(o: Object) : boolean +removeelementat(index: int) : void +setelementat(o: Object, index: int) : void +setsize(newsize: int) : void +trimtosize() : void Appends the element to the end of this vector Returns the current capacity of this vector Copies the elements in this vector to the array Returns the object at the specified index Returns an emulation of this vector Increases the capacity of this vector Returns the first element in this vector Inserts o to this vector at the specified index Returns the last element in this vector Removes all the elements in this vector Removes the first matching element in this vector Removes the element at the specified index Sets a new element at the specified index Sets a new size in this vector Trims the capacity of this vector to its size 17

18 อ นเตอร เฟส Enumeration ภายในคลาส Vector ม เมธอดช อ มเมธอดชอ elements( ) ท ส งค า ทสงคา กล บเป น Enumeration เมธอดท ส าค ญ boolean hasmoreelement() Object nextelement() 18

19 Example:Vector, Enumeration 1 import java.util.*; 2 3 public class TestVecotorEnumeration t ti { 4 public static void main(string[] args) { 5 Vector<String> v = new Vector<>(); 6 v.add("america"); 7 v.add("canada"); 8 v.add("russia"); 9 v.add("france"); 10 Enumeration e = v.elements(); 11 while(e.hasmoreelements()){ hasmoreelements()){ 12 System.out.println(e.nextElement()+","); 13 } 14 } 15 } output America, Canada, Russia, France, 19

20 The Map Interface The Map interface maps keys to the elements. The keys are like indexes. In List, the indexes are integer. In Map, the keys can be any objects. The HashMap class is a concrete implementation of the Map interface. ม การเก บค าค ย ค ก บค าข อม ลของสมาช กเสมอ ค ย ห ามซ คยหามซาแตขอม ลซาได าแต ข อมลซ าได 20

21 The Map Interface UML Diagram Map +clear(): void +containskey(key: Object): boolean +containsvalue(value: Object): boolean +entryset(): Set +get(key: Object): Object +isempty(): boolean +keyset(): Set +put(key: Object, value: Object): Object +putall(m: Map): void +remove(key: Object): Object +size(): int +values(): Collection Removes es all mappings from this map Returns true if this map contains a mapping for the specified key. Returns true if this map maps one or more keys to the specified value. Returns a set consisting of the entries in this map Returns the value for the specified key in this map Returns true if this map contains no mappings Returns a set consisting of the keys in this map Puts a mapping in this map Adds all mappings from m to this map Removes the mapping for the specified key Returns the number of mappings in this map Returns a collection consisting of values in this map 21

22 Example: HashMap 1 import java.util.*; 2 3 public class TestMap { 4 public static void main(string[] args) { m.put("3","russia"); Map<String,String> m = new HashMap<>(); m.put("1","america"); m.put("2","canada"); 9 m.put("4","america"); 10 System.out.println("Befor duplicate key:"+ m); 11 m.put("2","thailand"); 12 System.out.println("After duplicate key:"+m); 13 System.out.println("first one: "+m.get("1")); 14 } 15 } Befor duplicate key:{3=russia, 2=Canada, 1=America, 4=America} After duplicate key:{3=russia, 2=Thailand, 1=America, 4=America} first one: America 22