Collection Framework in java
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Collections Framework is a unified architecture for managing collections, Main Parts of Collections Framework 1. Interfaces :- Core interfaces defining common functionality exhibited by collections 2. Implementations :- Concrete classes of the core interfaces providing data structures 3. Operations :- Methods that perform various operations on collections
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Collection Framework in java
- 1. COLLECTION FRAMEWORK www.blog.cpd-india.com Call Us: 011-65164822 CPD TECHNOLOGIES Add:- Block C 9/8, Sector -7, Rohini , Delhi-110085, India www.cpd-india.com
- 2. COLLECTION 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 What is Collection? Collections Framework Collections Hierarchy Collections Implementations Set List Map
- 4. OBJECTIVES Define a collection Describe the collections framework Describe the collections hierarchy Demonstrate each collection implementation
- 5. WHAT IS A COLLECTION? A Collection (also known as container) is an object that contains a group of objects treated as a single unit. Any type of objects can be stored, retrieved and manipulated as elements of collections.
- 6. COLLECTIONS 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. COLLECTIONS FRAMEWORK INTERFACES Core Interface Description Collection specifies contract that all collections should implement Set defines functionality for a set of unique elements SortedSet defines functionality for a set where elements are sorted List 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. OPERATIONS Basic collection operations: Check if collection is empty Check if an object exists in collection. Retrieve an object from collection Add object to collection Remove object from collection Iterate collection and inspect each object Each operation has a corresponding method implementation for each collection type
- 10. COLLECTIONS CHARACTERISTICS Ordered Elements are stored and accessed in a specific order Sorted Elements are stored and accessed in a sorted order Indexed Elements can be accessed using an index Unique Collection does not allow duplicates
- 11. ITERATOR 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 ListSet LinkedHashSet TreeSet LinkedList Vector ArrayList implements implements implements implements extends extends
- 14. COLLECTION 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. LIST A List cares about the index. “Paul”“Paul” “Mark”“Mark” “John”“John” “Paul”“Paul” “Luke”“Luke”value index 0 1 2 3 4 LinkedListLinkedListVectorVectorArrayListArrayList
- 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. SET A Set cares about uniqueness, it doesn’t allow duplicates. “Paul”“Paul” “Mark”“Mark” “John”“John” “Luke”“Luke” “Fred”“Fred” “Peter”“Peter” TreeSetTreeSetLinkedHashSetLinkedHashSetHashSetHashSet
- 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” LinkedHashMapLinkedHashMap TreeMapTreeMapHashtableHashtableHashMapHashMap
- 24. MAP IMPLEMENTATIONS HASH MAP import java.util.HashMap; public class MyHashMap { public static void main(String args[ ]) { HashMap map = new HashMap( ); map.put("name", "Jody"); map.put("id", new Integer(446)); map.put("address", "Manila"); System.out.println("Name: " + map.get("name")); System.out.println("ID: " + map.get("id")); System.out.println("Address: " + map.get("address")); } } Name: Jody ID: 446 Address: Manila
- 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 MAPimport java.util.*; 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( )); } } } Printing the VALUES.... Manila 446 Jody
- 28. COLLECTION CLASSES SUMMARY NoBy indexXLinkedList NoBy indexXVector NoBy indexXArrayList NoBy insertion order or last access order XLinkedHashSet By natural order or custom comparison rules SortedXTreeSet NoNoXHashSet NoBy insertion order or last access order XLinkedHashMap By natural order or custom comparison rules SortedXTreeMap NoNoXHashtable NoNoXHashMap SortedOrderedListSetMapClass
- 29. KEY POINTS 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.
- 30. THANK YOU CPD TECHNOLOGIES Block C 9/8, Sector -7, Rohini, Delhi-110085, India Landmark: Near Rohini East Metro Station, Opposite Metro Pillar No-397 Telephone: 011-65164822 Mobile: +91- 8860352748 Email: support@cpd-india.com
Notes de l'éditeur
- Notes: A collection (sometimes called a container) is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve and manipulate data, and to transmit data from one method to another. Collections typically represent data items that form a natural group, like a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a collection of name-to-phone-number mappings).
- Notes: The Collections Framework in Java, which took shape with the release of JDK1.2 (the first Java 2 version) and expanded in 1.4 gives you lists, sets, and maps to satisfy most of your coding needs. They&apos;ve been tried, tested, and tweaked. Pick the best one for your job and you&apos;ll get - at the lest - reasonably good performance. And when you need something a little more custom, the Collections Framework in the java.util package is loaded with interfaces and utilities. Interfaces Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages like Java, these interfaces generally form a hierarchy. Implementation In essence, these are reusable data structures. Operations These algorithms are said to be polymorphic because the same method can be used on many different implementations of the appropriate collections interface. In essence, algorithms are reusable functionality
- Notes: Ordered A Hashtable collection is not ordered. Although the Hashtable itself has internal logic to determine the order (based on hashcodes), you won’t find any order when you iterate through the Hashtable. An ArrayList, however, keeps the order established by the elements’ index position (just like an array). LinkedHashSet keeps the order established by insertion, so the last element inserted is the last element in the LinkedHashSet (unlike an ArrayList where you can insert an element at a specific index position). Sorted You know how to sort alphabetically – A comes before B… For a collection of String objects, then the natural order is alphabetical. For Integer objects, the natural order is by numeric value. There is no natural order for self-defined classes unless or until the developer provides one, through an interface that defines how instances of a class can be compared to one another.
- Transition: Click the Red List Button to proceed to the topic on List. Click the Green Set Button to proceed to the topic on Set. Click the Blue Map Button to proceed to the topic on Map.
- Notes: A list cares about the index. The one thing that List has that non-lists don’t have is a set of methods related to the index. All three List implementations are ordered by index position – a position that you determine either by setting an object at a specific index or by adding it without specifying position, in which case the object is added to the end. Transition: Click ArrayList to view the sample solution. Click Vector to view the sample solution. Click Linked List to view the sample solution. Click the Red Area to go back to the previous slide.
- Vector is synchronized – only one thread can access it. Synchronization protects an object from multiple threads making modifications to an object’s state. Additionally, Hashtable is also synchronized.
- Notes: A Set cares about uniqueness – it doesn’t allow duplicates. Your good friend the equals( ) method determines whether two objects are identical (in which case only one can be in the se). The three Set implementations are described in the following sections. Transition: Click on the HashSet to view the sample solution. Click on the LinkedHashSet to view the sample solution. Click on the TreeSet to view the sample solution. Click the Green Area to go back to the previous slide.
- Notes: A Map cares about unique identifiers. You map a unique key (the ID) to a specific value, where both the key and the values are of course objects. You’re probably quite familiar with Maps since many languages support data structures that use key/value or name/value pair. Where the keys land in the Map is based on the key’s hashcode, so, like HashSet, the more efficient your hashCode( ) implementation, the better access performance you’ll get. The Map implementations let you do things like search for a value based on the key, as for a collection of just the values, or ask for a collection of just the keys. Transition: Click on the HashMap to view the sample solution. Click on the Hashtable to view the sample solution. Click on the LinkedHashMap to view the sample solution. Click on the TreeMap to view the sample solution. Click the Blue Area to go back to the previous slide.