2. C O L L E C TION
FRAMEWORK
The collections framework is a unified architecture for
representing and manipulating collections, enabling
them to be manipulated independently of the details
of their representation. It reduces programming effort
while increasing performance. It enables
interoperability among unrelated APIs, reduces effort
in designing and learning new APIs, and fosters
software reuse. The framework is based on more than
a dozen collection interfaces. It includes
implementations of these interfaces and algorithms to
manipulate them.
3. CONTENTS
𝗈 What is C ollection?
𝗈 C ollections Framework
𝗈 C ollections Hierarchy
𝗈 Collections Implementations
● Set
● List
● Map
4. OB JE CTIVE S
𝗈 Define a collection
𝗈 Describe the collections framework
𝗈 Describe the collections hierarchy
𝗈 Demonstrate each collection implementation
5. WHAT IS A COLLECTION?
𝗈 A Collection (also known as container) is an object that contains a
group of objects treated as a single unit.
𝗈 Any type of objects can be stored, retrieved and manipulated as
elements of collections.
6. CO L L ECT IO N S FRAMEWORK
Collections Framework is a unified architecture for
managing collections
Main Parts of Collections Framework
1. Interfaces
Core interfaces defining common functionality exhibited by
collections
1. Implementations
Concrete classes of the core interfaces providing data structures
1. Operations
Methods that perform various operations on collections
7. C OLLE C TIONS FRAMEWORK
INTERFACES
CoreInterface Description
Collection
Set
SortedSet
List
specifies contract that all collections should implement
defines functionality for a set of unique elements
defines functionality for a set where elements are sorted
defines functionality for an ordered list of non- unique elements
Map defines functionality for mapping of unique keys to values
SortedMap defines functionality for a map where its keys are sorted
8. COLLECTIONS FRAMEWORK
IMPLEMENTATIONS
Set List Map
HashSet ArrayList HashMap
LinkedHashSet LinkedList LinkedHashMap
TreeSet Vector Hashtable
Tree Map
Note: Hashtable uses a lower-case “t”
9. OPE RATIONS
Basic collection operations:
𝗈 Check if collection is empty
𝗈 Check if an object exists in collection.
𝗈 Retrieve an object from collection
𝗈 Add object to collection
𝗈 Remove object from collection
𝗈 Iterate collection and inspect each object
● Each operation has a corresponding method implementation for
each collection type
10. CO L L ECT IO N S
C HARAC T E RISTIC S
𝗈 Ordered
● Elements are stored and accessed in a specific
order
𝗈 Sorted
● Elements are stored and accessed in a sorted
order
𝗈 Indexed
● Elements can be accessed using an index
𝗈 Unique
● Collection does not allow duplicates
11. ITERATOR
𝗈 An iterator is an object used to mark a position in a
collection of data and to move from item to item within
the collection
Syntax:
Iterator <variable> = <CollectionObject>.iterator();
12. COLLECTIONS HIERARCHY
SET AND LIST
HashSet
Collection
SortedSet
List
Set
LinkedHashSet TreeSet LinkedList Vector ArrayList
implements
implements
implements
implements extends
extends
14. CO L L ECT IO N IMPLEMENTATIONS
Set : Unique things (classes that implement Set)
Map : Things with a unique ID (classes that implement Map)
List : Lists of things (classes that implement List)
15. L IST
A List cares about the index.
“Paul”
“Paul” “Mark”
“Mark” “John”
“John” “Paul”
“Paul” “Luke”
“Luke”
value
index 0 1 2 3 4
LinkedList
Vector
ArrayList
16. LIST IMPLEMENTATIONS
ARRAY LIST
import java.util.ArrayList;
public class MyArrayList {
public static void main(String args[ ]) {
ArrayList alist = new ArrayList( );
alist.add(new String("One"));
alist.add(new String("Two"));
alist.add(new String("Three"));
System.out.println(alist.get(0));
System.out.println(alist.get(1));
System.out.println(alist.get(2));
}
}
One
Two
Three
17. LIST IMPLEMENTATIONS
VECTOR
import java.util.Vector;
public class MyVector {
public static void main(String args[ ]) {
Vector vecky = new Vector( );
vecky.add(new Integer(1));
vecky.add(new Integer(2));
vecky.add(new Integer(3));
for(int x=0; x<3; x++) {
System.out.println(vecky.get(x));
}
}
}
1
2
3
18. LIST IMPLEMENTATIONS
LINKED LIST
import java.util.LinkedList;
public class MyLinkedList {
public static void main(String args[ ]) {
LinkedList link = new LinkedList( );
link.add(new Double(2.0));
link.addLast(new Double(3.0));
link.addFirst(new Double(1.0));
Object array[ ] = link.toArray( );
for(int x=0; x<3; x++) {
System.out.println(array[x]);
}
}
}
1.0
2.0
3.0
19. S E T
A Set cares about uniqueness, it doesn’t allow duplicates.
“Paul”
“Paul”
“Mark
”
“Mark”
“John”
“John”
“Luke”
“Luke”
“Fred”
“Fred”
“Peter”
“Peter”
TreeSet
LinkedHashSet
HashSet
20. SET IMPLEMENTATIONS
HASH SET
import java.util.*;
public class MyHashSet {
public static void main(String args[ ]) {
HashSet hash = new HashSet( );
hash.add("a");
hash.add("b");
hash.add("c");
hash.add("d");
Iterator iterator = hash.iterator( );
while(iterator.hasNext( )) {
System.out.println(iterator.next( ));
}
}
}
d
a
c
b
21. SET IMPLEMENTATIONS
LINKED HASH SET
import java.util.LinkedHashSet;
public class MyLinkedHashSet {
public static void main(String args[ ]) {
LinkedHashSet lhs = new LinkedHashSet();
lhs.add(new String("One"));
lhs.add(new String("Two"));
lhs.add(new String("Three"));
Object array[] = lhs.toArray( );
for(int x=0; x<3; x++) {
System.out.println(array[x]);
}
}
}
One
Two
Three
22. SET IMPLEMENTATIONS
TREE SET
import java.util.TreeSet;
import java.util.Iterator;
public class MyTreeSet {
public static void main(String args[ ]) {
TreeSet tree = new TreeSet();
tree.add("Jody");
tree.add("Remiel");
tree.add("Reggie");
tree.add("Philippe");
Iterator iterator = tree.iterator( );
while(iterator.hasNext( )) {
System.out.println(iterator.next( ).toString( ));
}
}
}
Jody
Philippe
Reggie
Remiel
23. MAP
A Map cares about unique identifiers.
“Paul”
“Paul” “Mark
”
“Mark” “John”
“John” “Paul”
“Paul” “Luke”
“Luke”
key
value
“Pl” “Ma” “Jn” “ul” “Le”
LinkedHashMap TreeMap
Hashtable
HashMap
25. MAP IMPLEMENTATIONS
HASH TABLE
import java.util.Hashtable;
public class MyHashtable {
public static void main(String args[ ]) {
Hashtable table = new Hashtable( );
table.put("name", "Jody");
table.put("id", new Integer(1001));
table.put("address", new String("Manila"));
System.out.println("Table of Contents:" + table);
}
}
Table of Contents:
{address=Manila, name=Jody, id=1001}
26. MAP IMPLEMENTATIONS
LINKED HASH MAP
import java.util.*;
public class MyLinkedHashMap {
public static void main(String args[ ]) {
int iNum = 0;
LinkedHashMap myMap = new LinkedHashMap( );
myMap.put("name", "Jody");
myMap.put("id", new Integer(446));
myMap.put("address", "Manila");
myMap.put("type", "Savings");
Collection values = myMap.values( );
Iterator iterator = values.iterator( );
while(iterator.hasNext()) {
System.out.println(iterator.next( ));
}
}
}
Jody
446
Manila
Savings
27. MAP IMPLEMENTATIONS
TREE MAP
public class MyTreeMap {
public static void main(String args[]) {
TreeMap treeMap = new TreeMap( );
treeMap.put("name", "Jody");
treeMap.put("id", new Integer(446));
treeMap.put("address", "Manila");
Collection values = treeMap.values()
Iterator iterator = values.iterator( );
System.out.println("Printing the VALUES....");
while (iterator.hasNext()) {
System.out.println(iterator.next( ));
}
}
}
import java.util.*;
Printing the VALUES....
Manila
446
Jody
28. CO L L ECT IO N C L A S S E S SUMMARY
Class Map Set List Ordered Sorted
HashMap X No No
Hashtable X No No
TreeMap X Sorted By natural order or
custom comparison rules
LinkedHashMap X By insertion order or
last access order
No
HashSet X No No
TreeSet X Sorted By natural order or
custom comparison rules
LinkedHashSet X By insertion order or
last access order
No
ArrayList X By index No
Vector X By index No
LinkedList X By index No
29. KEY POINTS
𝗈 Collections Framework contains:
1. Interfaces
2. Implementations
3. Operations
A list cares about the index.
A set cares about uniqueness, it does not allow
duplicates.
A map cares about unique identifiers.
𝗈
𝗈
𝗈
