![16
Public static void main(String arg[]){
Vectorv=newvector();
For(int i=0; i<=10; i++){
v.addelement(i);}
System.out.print(al); //0,1,2β¦β¦..10;
Enumeration e=v.element();
While(itr.hasNextElement()){
Integer in=(Integer)itr.nextElement();
If(in%2==0)
System.out.println(in); //0,2,4,6,8,10
}
System.out.print(al); //0,1,2β¦β¦..10
}
1. 1 Vector](https://image.slidesharecdn.com/collection-160616100154/85/Collection-16-320.jpg)
![19
Public static void main(String arg[]){
ArrayList al=new ArrayList();
For(int i=0; i<=10; i++){
al.add(i);}
System.out.print(al); //0,1,2β¦β¦..10;
Iterator itr=al.iterator();
While(itr.hasNext()){
Integerin=(Integer) itr.next();
If(in%2==0)
System.out.println(in); //0,2,4,6,8,10
Else
itr.remove();
}
System.out.print(al); //0,2,4,6,8,10
}
1. Arraylist](https://image.slidesharecdn.com/collection-160616100154/85/Collection-19-320.jpg)
![1. Arraylist
20
Two ways to iterate the elements of collection in java
β’ By Iterator interface.
β’ By for-each loop.
import java.util.*;
class TestCollection1{
public static void main(String args[]){
ArrayList<String> al=new ArrayList<String>();//creating arraylist
al.add("Ravi");//adding object in arraylist
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator itr=al.iterator();//getting Iterator from arraylist to traverse eleme
nts
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}](https://image.slidesharecdn.com/collection-160616100154/85/Collection-20-320.jpg)
![1. Arraylist
21
import java.util.*;
class TestCollection2{
public static void main(String args[]){
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
for(String obj:al)
System.out.println(obj);
}
}](https://image.slidesharecdn.com/collection-160616100154/85/Collection-21-320.jpg)
![24
import java.util.*;
public class TestCollection7{
public static void main(String args[]){
LinkedList<String> al=new LinkedList<String>()
;
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator<String> itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Ravi
Vijay
Ravi
Ajay](https://image.slidesharecdn.com/collection-160616100154/85/Collection-24-320.jpg)
![HashSet class (continue)
31
import java.util.*;
class TestCollection9{
public static void main(String args[]){
HashSet<String> al=new HashSet<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator<String> itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Vijay
Ravi
Ajay](https://image.slidesharecdn.com/collection-160616100154/85/Collection-31-320.jpg)
![2.2 TreeSet class (α)
33
import java.util.*;
class TestCollection11{
public static void main(String args[]){
TreeSet<String> al=new TreeSet<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator<String> itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Ajay
Ravi
Vijay](https://image.slidesharecdn.com/collection-160616100154/85/Collection-33-320.jpg)
Collection
- 1. Java Presentation αααααααα αααΌα αα αα αα αα ααα α ααΈ Korea Software HRD Center α£αααααααΉααΆααααα: αααα α·α ααΈαβαααααα» α www.kshrd.com.kh α£αααααααααΆ: ααα αα ααα»α αααα»α ααα ααΆααα αααα α·αα
- 2. αααα αα αααααΆααα ααα α»αααΈ α€ αααααΆαααα Collection αααΆααα·α 1. ααα α αα»α ααα 2. ααα ααΆααΈααα 3. ααα αα αααααΆ 4. ααα ααΉα ααΈααΆ 5. ααα ααΈα ααα α
- 3. ααΆαα·ααΆ 1. αααα ααααα’αααΈ Collections 2. αααα ααααα’αααΈ List:Vector, ArrayList, LinkedList 3. αααα ααααα’αααΈ Set: HashSet,TreeSet 4. αααα ααααα’αααΈ Map: TreeMap,HashTable
- 4. 1. αααα ααααα’αααΈ Collections ο± Collection Class αα αα α»αααΆα Java ααΊααΆ Container ο± Collection Class ααΆαα½αααα α» ααα Class αα·α Interface αα½αα²ααα’ααααααααααα α·ααΈαααααααα½α α αααααα collection αα Object ο± ααΆαααααΆ Object αα½ααααααααααΆαααΆαααΆαααααΎαααααααααΌαααΆα ααααΌααα½ααααα ααααα½α (Single Unit)α ο± Collections ααααΌαααΆααααααΎααααΆααααΆαααΎαααΈ αααΆαα ααΆααα αααααα αα·α ααααα·ααααα α ο± ααΆααΌαα αα½αααΆααααΆαα²αα data items ααααααΆ form natural group ααΌαααΆ game poker hand(a collection of cards),mail folder(a collection of letter) ααΆαααΎα α 1.1 αααΎα’ααΈαα ααΆ Collections?
- 5. 1. αααα ααααα’αααΈ Collections ο± Collection framework ααΊααΆααΆααα½ααααα αΌα architecture ααααΆααααΆααααααΆ α αα·α ααΆααααααΎααααΆαα collections α ο± ααΆααααααΆαααααααΊααΆ Collection frameworkα β’ Interfaces:ααΆααΊααΆ abstract data types αααααααααΆ αααΈ Collections α Interface α’αααααΆ αα·α²αα Collections α’αΆαααααΌαααΆααααααΎααααΆααα αααα αΈ ααΌαααΆααααααΆ αααΈααΆαααα’α·ααααααα½αααΆ α β’ Implementations: ααΆααΆααΆαα’ααααααΆαα αααα αααΌα Collections interfaces α ααααααααΆααααααααΆααΊα’αΆααααααΎααααΆααα αΎαα α·ααα data structure α 1.1 αααΎα’ααΈαα ααΆ Collections Framework?
- 6. 1. αααα ααααα’αααΈ Collections β’ Algorithms:ααΆααΊααΆ methods ααααα’ααααααΆαααααΆααααΆα αααααααα ααΌαααΆ ααΆαααααααααΆα αα·α αααααα αα αααΎ Object ααααα’α αααααΌααααΎ collection interfaces α Algorithms ααααΌαααΆααααα ααΆ polymorphic ααααααΌααααα αα ααΉα methods ααααα’αΆαααααΎααΆααααααΎααα ααααα ααΆα collections interfaces α ααααααααΆααααααααΆααΊα’αΆααααααΎ ααααΆααα αΎαα α·ααα functionality α
- 7. 1. αααα ααααα’αααΈ Collections ο± Reduces programming effort:ααΆααΆααααααααΌα data structure αα·α algorithms ααΌαααααα’αααα·αα αααΆααααΆα αααααα αα·α ααα ααα αααΎαα·αα ααΆαααααα’ααααααΎαααΆαα ααΆααα αΎα α ααΆααΆααα½αααααα½αααα API αα½ααααα½ααααααα·αααΆαααα α αααα ααα²ααα ααα·αα αααΆααααααα adapter object α¬ αα ααααααΌααααΎαααΈ connect API α αΎα α ο± Increases program speed and quality: ααΆααΆααααααααΌα high-performance high-quality αααααΆαα’αααααα data structure αα·α algorithms α²ααααΆαα ααααα’ α ααΆααααααΆ α’ααααααααααα α·ααΈαα·αααΆααα αααααΏααα α’αα α»αααααα structure α αααα α½αα―α αα αΎααααΎαααΉαααΆααααααααααααΎααααΎαααΈααααΎα²ααααα 1.1 αααααααα·αα Collections Framework?
- 8. 1. αααα ααααα’αααΈ Collections ο± Allows interoperability among unrelated APIs: Collection interfaces ααΊααΆ ααΆαααααααα αα α»αααααααααΆαα½α αα αΎα API ααΆαΆ αα collection αα αα α·ααα αα α ααααα·ααααΎ network administration API αααααα²αα collection node name ο± Increases program speed and quality: ααΆααΆααααααααΌα high-performance high-quality αααααΆαα’αααααα data structure αα·α algorithms α²ααααΆαα ααααα’ α ααΆααααααΆ α’ααααααααααα α·ααΈαα·αααΆααα αααααΏααα α’αα α»αααααα structure α αααα α½αα―α αα αΎααααΎαααΉαααΆααααααααααααΎααααΎαααΈααααΎα²ααααα αα α·ααΈα α·ααααααααααΎαα αΎα α
- 9. 1. αααα ααααα’αααΈ Collections ο± Java αααααα²αααα αααααααα Collection αα½ααααα½αααΌαααΆα Set:αα·αα’αΆαααΆα element αα α½ααααα ,αα αΎα order ααΊαα·αα αααΆααααΆα αα αααα οΌ SortedSet: ααΌαααΆ Set ααααα order α αααΆααα α·α οΌ List: α’αΆαααΆα element αα α½ααααα αα αΎα order ααΊααααΌααααααΆααα αα α ο± Java αααααααα²ααααΌα Collection-like αα½ααααα½αααΌαααΆα οΌ Map: βdictionaryβ αααα associates key αα·α value ααααα order ααΊαα·αα αααΆααααΆααα αααα 1.1 αααααααα Collections?
- 10. 1. αααα ααααα’αααΈ Collections
- 11. 1. αααα ααααα’αααΈ Collections 11
- 12. 1. List Interface 12 οGenerate result ααΆα insertion order. οααΆ Support duplicacy οααΆ Support indexing ααΆααααααΆαααΎαα’αΆα insert element ααΆα index ααΆααααΆααααΆαα οααΆα’αΆα synchronized αα·ααα·α synchronized ααΆαααΆααααΈα.
- 13. 1. List Interface A List cares about the index. βPaulβ βMarkβ βJohnβ βPaulβ βLukeβvalue index 0 1 2 3 4 LinkedListVectorArrayList
- 14. List ArrayLi st LinkedLi st Vecto r Fast iteration and fast random access Good for adding elements to the ends, i.e. stacks and queues It's like a slower ArrayList, but it has synchronize d methods
- 15. 1. 1 Vector 15 ο ααΆααααΌαααΆααααααΎααΆαΆααααΈ Java versoin 1.0 ααα ο Generate result ααΆα insertion order. ο ααΆ support duplicacy. ο ααΆ Increase capacity size ααΈααααα capacity αααΎαααΆ ο ααΆααααΌαααΆαααααααΆ ααααΆααΆ legacy class(old class) . ο ααΆααΆαααααα synchronized α¬ thread-safe. ο αααααααααΆααΆαααααα synchronization ααΆααααΎαα’αΆα Process slow ααΌαα ααααααα·αααΌαααΆααααααΎααΆααα ο ααΆααΆαααααα dynami
- 16. 16 Public static void main(String arg[]){ Vectorv=newvector(); For(int i=0; i<=10; i++){ v.addelement(i);} System.out.print(al); //0,1,2β¦β¦..10; Enumeration e=v.element(); While(itr.hasNextElement()){ Integer in=(Integer)itr.nextElement(); If(in%2==0) System.out.println(in); //0,2,4,6,8,10 } System.out.print(al); //0,1,2β¦β¦..10 } 1. 1 Vector
- 17. 1. Arraylist 17 β’ αααααΎαααα Dynamic Array αααΎαααΈstore element(αααα»αααΆαα»)α β’ α’αΆα αααα»α Duplicate element(ααΆαα»αααΌα)α β’ Maintaininsertion order (ααΆαααΆααααααΆαααα)α β’ Non synchronized β’ α’αα»ααααΆ αααΆα Random access ααααααααΆααααΎααΆαααΆαααα indexα β’ αααΎαα’αΆα Iterate element ααcollection ααα»α Java ααΆαα’αααααααΉ: Iterator interface & For-each Loop
- 19. 19 Public static void main(String arg[]){ ArrayList al=new ArrayList(); For(int i=0; i<=10; i++){ al.add(i);} System.out.print(al); //0,1,2β¦β¦..10; Iterator itr=al.iterator(); While(itr.hasNext()){ Integerin=(Integer) itr.next(); If(in%2==0) System.out.println(in); //0,2,4,6,8,10 Else itr.remove(); } System.out.print(al); //0,2,4,6,8,10 } 1. Arraylist
- 20. 1. Arraylist 20 Two ways to iterate the elements of collection in java β’ By Iterator interface. β’ By for-each loop. import java.util.*; class TestCollection1{ public static void main(String args[]){ ArrayList<String> al=new ArrayList<String>();//creating arraylist al.add("Ravi");//adding object in arraylist al.add("Vijay"); al.add("Ravi"); al.add("Ajay"); Iterator itr=al.iterator();//getting Iterator from arraylist to traverse eleme nts while(itr.hasNext()){ System.out.println(itr.next()); } } }
- 21. 1. Arraylist 21 import java.util.*; class TestCollection2{ public static void main(String args[]){ ArrayList<String> al=new ArrayList<String>(); al.add("Ravi"); al.add("Vijay"); al.add("Ravi"); al.add("Ajay"); for(String obj:al) System.out.println(obj); } }
- 22. 1. 2 Vector VS Arraylist 22 ArrayList Vector 1) ArrayList is not synchronized. Vector is synchronized. 2) ArrayList increments 50% of current array size if number of element exceeds from its capacity. Vector increments 100% means doubles the array size if total number of element exceeds than its capacity. 3) ArrayList is not a legacy class, it is introduced in JDK 1.2. Vector is a legacy class. 4) ArrayList is fast because it is non-synchronized. Vector is slow because it is synchronized i.e. in multithreading environment, it will hold the other threads in runnable or non- runnable state until current thread releases the lock of object. 5) ArrayList uses Iterator interface to traverse the elements. Vector uses Enumeration interface to traverse the elements. But it can use Iterator also.
- 23. 1. 3 Linked List 23 β’ ααΆααααΌαααΆααααααΎααΆαΆααααΈJava version 1.2ααα β’ αααααΎααααDoubly linkedlist αααΎαααΈ store elementα β’ α’αΆα αααα»α Duplicate element(ααΆαα»αααΌα)α β’ Maintaininsertion order (ααΆαααΆααααααΆαααα)α β’ Non synchronizedα β’ α’αΆα αααααΎααΆList αααα stackqueueα
- 24. 24 import java.util.*; public class TestCollection7{ public static void main(String args[]){ LinkedList<String> al=new LinkedList<String>() ; al.add("Ravi"); al.add("Vijay"); al.add("Ravi"); al.add("Ajay"); Iterator<String> itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } } Ravi Vijay Ravi Ajay
- 25. 1. 4 Linked List VS ArrayList 25 ArrayList LinkedList 1) ArrayList internally uses dynamic array to store the elements. LinkedList internally uses doubly linked list to store the elements. 2) Manipulation with ArrayList is slow because it internally uses array. If any element is removed from the array, all the bits are shifted in memory. Manipulation with LinkedList is faster than ArrayList because it uses doubly linked list so no bit shifting is required in memory. 3) ArrayList class can act as a list only because it implements List only. LinkedList class can act as a list and queue both because it implements List and Deque interfaces. 4) ArrayList is better for storing and accessing data. LinkedList is better for manipulating data.
- 26. 2. Set Interface 26 ο ααΆααΆαααΆαΆααααΈ Java 1.2 ο ααΆαα·αα’αα»ααααΆ ααα’αΆαααΆα Dupplicate αα αα»αααααααΎαααΎααα’αΆαααΆααααα Dupplicate ααααΆαα·αααΆα Error αααΎαα αΎααααα ο ααΆαα·α support indexing ααα ααΆααααααΆ ααΆαα·αααΆαααΆα insert αα·α delete elements ααΆα index ααΆαα½αα αΎαα
- 27. Hierarchy of HashSet class: 27
- 28. 2. Set Interface A Set cares about uniqueness, it doesnβt allow duplicates. βPaulβ βMarkβ βJohnβ βLukeβ βFredββPeterβ TreeSetLinkedHashSetHashSet
- 29. Set HashSet LinkedHashSet TreeSet Fast access, assures no duplicates, provides no ordering No duplicates; iterates by insertion order No duplicates; iterates in sorted order
- 30. 2.1 HashSet class 30 ο ααΆααααΌαααΆααααααΎααΆαΆααααΈ Java Version 1.2 αααααα ο ααΆαα·α Support Dupplicate ααα ο It doesn't guarantee any order for generating result even it does not guarantee that the order will remain constant over time. ο ααΆα’αα»ααααΆ ααα’αΆαααΆα null ααΆ elementα ααΆααααααΆααΆαα·αααΆα NullPointerException αααΎαα αΎααααααααΆα element ααΆ Null ο ααΆααααΌαααΆαααΌα Hashtable class αααΎαααΈ holding elements ααααααΆα ο ααΆαα·αααΆααααααααΆ synchronized ααααααααΎαα’αΆα ααααΎαα’αΆαααΆ synchronized ααΆααα ααΆααααααΌαααΆαα ο αααααΎααΌα hashtable αααΎαααΈ store ααΌα elements ααααααΆα ο ααΆ extends αα αααΈ AbstractSet class αα·α implements αα αααΈ Set interface. ο αααα»αααα unique elements ααααα»αααΆα ααα
- 31. HashSet class (continue) 31 import java.util.*; class TestCollection9{ public static void main(String args[]){ HashSet<String> al=new HashSet<String>(); al.add("Ravi"); al.add("Vijay"); al.add("Ravi"); al.add("Ajay"); Iterator<String> itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } } Vijay Ravi Ajay
- 32. 2.2 TreeSet class 32 οααΆααααΌαααΆααααααΎααΆαΆααααΈ Java version 1.2 ααα οααΆαα·α support ααΌα duplicacy ααα οααΆ generate ααΌαααΆα Order ααααααααΆααααα ascending ααααααΎαααα’αΆα αα’αΆαααΆ generate ααΆα descending ααΆαααααα οααΆαααα»αααα unique elements ααΌα HashSet ααααα οααΆ implements αα αααΈ NavigableSet interface αααα extends ααΈ SortedSet interface.
- 33. 2.2 TreeSet class (α) 33 import java.util.*; class TestCollection11{ public static void main(String args[]){ TreeSet<String> al=new TreeSet<String>(); al.add("Ravi"); al.add("Vijay"); al.add("Ravi"); al.add("Ajay"); Iterator<String> itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } } Ajay Ravi Vijay
- 34. 3. Map Interface 34 ο ααΆααΆαααΆαΆααααΈ Java 1.2ααα ο ααΆααααΎααΆααααααααΆ key-value paired techniques(Hashing techniques). ο ααΆαα·αα’αΆα ααΆα duplicate ααΆααααα»ααααααΆα’αΆα ααΆα duplicate values. ο ααΆαα·αααΆααααααsynchronized ααα
- 36. Map A Map cares about unique identifiers. βPaulβ βMarkβ βJohnβ βPaulβ βLukeβ key value βPlβ βMaβ βJnβ βulβ βLeβ LinkedHashMap TreeMapHashtableHashMap
- 37. Map World Map Hashtab le LinkedHashM ap Treemap Like a slower HashMap (as with Vector, due to its synchronized methods). No null values or null keys allowed Faster iterations; iterates by insertion order or last accessed; allows one null key, many null values A sorted map HashMap Fastest updates (key/values); allows one null key, many null values
- 38. 3. αααα ααααα’αααΈ TreeMap & HashTable ο± ααΊααΆ class αααα implements αααααΈ NavigableMap interface αα·ααextends αααααΈα AbstractMap class ο± ααΆααα α»αααΌα value α αααααα’ααααΎ key ααααααΆ ο± ααΆαα·αα’αΆααααα α keyαα αααα’αΆααααα α Value ααΆα ο± ααΆααα α»αααΆαααα unique elements ααααΆα αα ο± ααΆαααααααααΆ ascending 3.1. TreeMap
- 39. 3. αααα ααααα’αααΈ TreeMap & HashTable 3.1.1 Constructor αααα TreeMap ο±TreeMap(): ααΆ constructor αααααααααΎαααΎαααΈαααααΎα empty tree map αααααααααααααααα ascending ααΆα key value ααααααΆα ο±TreeMap(Comparator comp): αααααΎαααΎαααΈαααααΎα empty tree-based map αααααααααααααΆα Comparator compα ο±TreeMap(Map m): constructor ααααααΊ ααααααααααα αα’αΆα tree map ααΆαα½αααΉαααΆα m ααααααΆααΉααααααααααααα ascending ααΆα key value ααααααΆα ο±TreeMap(SortedMap sm): ααΆααααααααααα αα’αΆα tree map ααΆαα½αααΉαααΆαααΈ SortedMap sm ααααααΆαααααααααΌαααΉα sm ααααα
- 40. 3. αααα ααααα’αααΈ TreeMap & HashTable 3.2 Methods αααα TreeMap Method Desciption void Clear() remove all mapping from this treemap Object Clone() return a shallow copy αααααTreeMap instance Comparator comparator() return comparator αααααααααΎαααΎαααΈααααααα Boolean containsKey (object key) Return true αααΎαtreemap ααααααΆαααα α»αααΌα specified key αααααmapping Boolean containsValue(object Return true αααΎ treemap αααα map αα ααΆαα keyαα½αα¬ αααααΎαααααααΆα specified valueαααα Set entrySet() Return a set view of the mapping contained in this map.
- 41. 3. αααα ααααα’αααΈ TreeMap & HashTable ο± HashTable implements ααΈ Map Interface αα·ααextends ααΈ Dictionary Class ο± ααΆααα α»αααΌα value α αααΉαααααα’ααααΎ key ο± ααΆααα α»αααααunique elements ο± ααΆααΌαααΉα HashMap αααααααααααααααααΆααΊ synchronized ο± ααΆαα·ααααααααααΌααα ααΉα TreeMap αα 3.3 HashTable
- 42. 3. αααα ααααα’αααΈ TreeMap & HashTable 3.3 Methods αααα HashTable Method Desciption void clear() remove key value ααΆααα’αααα·αhashtable Object Clone() return a shallow copy ααΈ hashtable αααα boolean contains(Object value) Test αααΎαkey map αα ααΆααspecified value boolean isEmpty() Test αααΎ hashtable maps αααα α keyαα ααΆααvalue Enumeration keys() Return ααΌαααΆαααΆααααα αααα keys ααααααΆααα α»α hashtable Object put(object key,object value) Maps αα specified key αα ααΆααspecified value
- 43. 3. αααα ααααα’αααΈ TreeMap & HashTable 3.3 Methods αααα HashTable Method Desciption void rehash() αααααΎαααα ααα hashtableαα·ααααααΎα keys ααΆααα’αα ααΆ object remove(object key) remove keyαα·ααvalue αααα key αααΆαα int size() Return αααα½α key-value αααααααα map String toString() Return string ααααααααΌα Boolean key) Test αααΎ specified object ααΊααΆ keyαα α»α hashtable Boolean containValue(object value) Test αααΎ specified object ααΊααΆ valueαα α»α hashtableα return false ααααα·αααΆαvalue ααΆααα αΎα
- 44. 3. αααα ααααα’αααΈ TreeMap & HashTable 3.3 Methods αααα HashTable Method Desciption Enumeration elements() Return ααΌαααΆαααΆααααα αααα value ααααααΆααα α»α hashtable object get(object key) remove keyαα·ααvalue αααα key αααΆαα
- 45. ααααααα―αααΆ 45 β’ http://tutorials.jenkov.com/java-collections/index.html β’ http://www.javatpoint.com/Map-interface-in-collection- framework β’ http://www.javamadesoeasy.com/2015/04/arraylist-in- java.html β’ http://www.javamadesoeasy.com/2015/04/arraylist-in- java.html β’ http://hackersstudy.tistory.com/26 β’ http://www.javaperspective.com/collections.html β’ https://developer.apple.com/library/ios/documentation/Swift/ Conceptual/Swift_Programming_Language/CollectionTypes .html β’ https://docs.oracle.com/javase/tutorial/collections/intro/ β’ http://www.javatpoint.com/collections-in-java
Editor's Notes
- AΒ collectionΒ β sometimes called a container β is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language β or just about any other programming language β you are already familiar with collections.
- AΒ collectionΒ β sometimes called a container β is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language β or just about any other programming language β you are already familiar with collections.
- AΒ collectionΒ β sometimes called a container β is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language β or just about any other programming language β you are already familiar with collections.
- AΒ collectionΒ β sometimes called a container β is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language β or just about any other programming language β you are already familiar with collections.
- AΒ collectionΒ β sometimes called a container β is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language β or just about any other programming language β you are already familiar with collections.
- Java supplies several types of Collection: Set: cannot contain duplicate elements, order is not important SortedSet: like a Set, but order is important List: may contain duplicate elements, order is important Java also supplies some βcollection-likeβ things: Map: a βdictionaryβ that associates keys with values, order is not important SortedMap: like a Map, but order is important While you can get all the details from the Java API, you are expected to learn (i.e. memorize): The signatures of the βmost importantβ methods in each interface The most important implementations of each interface
- Java supplies several types of Collection: Set: cannot contain duplicate elements, order is not important SortedSet: like a Set, but order is important List: may contain duplicate elements, order is important Java also supplies some βcollection-likeβ things: Map: a βdictionaryβ that associates keys with values, order is not important SortedMap: like a Map, but order is important While you can get all the details from the Java API, you are expected to learn (i.e. memorize): The signatures of the βmost importantβ methods in each interface The most important implementations of each interface
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