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    Presentation1 Presentation1 Presentation Transcript

    • The Collection Framework
    • Collections Framework A collection is a group of objects. The Collection Framework Standardizes the way in which group of objects are handled by your program.What c++ calls a Container,Java calls a Collection
    • The Collection interfaces Collection- enable you to work with groups of objects. List- extends collection to handle sequences. Set- extends collection to handle sets, which must contain unique elements.
    • The Collection Classes ArrayList – implements a dynamic array. LinkedList – implements a linked list. HashSet – uses hash table. linkedHashSet – allow insertion-order iterations. TreeSet – implements a set stored in a tree.
    • ArrayList class ArrayList class implements the List interface. ArrayList supports dynamic arrays that can grow as needed. It is a Variable length array of object references. ArrayLists are created with an initial size. When this size is enlarged, the collection is automatically enlarged. And when the objects are removed, the array may be shrunk.
    • Using constructor ArrayList() ArrayList(Collection c) ArrayList(int capacity)
    • Methods and Examples Create an array list ArrayList a1 = new ArrayList(); Add elements to the array list a1.add(“c”); a1.add(1,“A2”);
    •  Display the array list System.out.println(a1); Remove elements from the array list a1.remove(“F”); a1.remove(2); For finding the size of arrayList a1.size();
    • Obtaining an Array from an ArrayList Add elements to the array list a1.add(new Integer(1)); Get array object ia[ ] = a1.toArray();
    • LinkedList Class LinkedList class extends AbstractSequentialList and implements the List interface. It provides a linked list data structure.
    • Constructor LinkedList() LinkedList(collection c)
    • Methods To add elements at the first /last position. addFirst(); addLast(); To retrieve the elements at first /last position. getFirst(); getLast(); To remove the elements at first /last position. removeFirst(); removeLast();
    • TreeSet class TreeSet provides an implementations of the Set interface that uses a tree for storage. Objects are stored in sorted order i.e ascending order. Access and retrieval times are quite fast.
    • Constructors TreeSet() TreeSet(collection c) TreeSet(comparator comp) TreeSet(SortedSet ss)
    • ExampleImport java.util.*;Class TreeSetDemo{Public static void main(String args[]){TreeSet ts=new TreeSet();ts.add(“C”);ts.add(“A”);ts.add(“B”);System.out.println(ts);}}Output- [A,B,C]
    • HashSet class HashSet extends AbstractSet and implements the Set interface. It creates a collection that uses a hash table for storage. Basic operations: add() contains() remove() size()
    • Using constructor HashSet() HashSet(collection c) HashSet(int capacity) HashSet(int capacity, float fillRatio)
    • Methods boolean add(Object o) void clear() Object clone() boolean contains(Object o) boolean isEmpty() Iterator iterator() boolean remove(Object o) int size()
    • Exampleimport java.util.*;class hashset{public static void main(String args[]){HashSet hs = new HashSet();hs.add("B");hs.add("A");hs.add("D");hs.add("E");hs.add("C");hs.add("F");System.out.println(hs);hs.remove("C");System.out.println("elements after removing C"+hs); } }
    • LinkedHashSet class LinkedHashSet extends HashSet, but adds no members of its own. LinkedHashSet maintains a linked list of the entries in the set.
    • Using constructor LinkedHashSet( ) LinkedHashSet(Collection c) LinkedHashSet(int capacity) LinkedHashSet(int capacity, float fillRatio)
    • Remove all elements from LinkedHashSetimport java.util.LinkedHashSet; public class linkedhashset { public static void main(String[] args) { LinkedHashSet lhashSet = new LinkedHashSet(); lhashSet.add(new Integer("1")); lhashSet.add(new Integer("2")); lhashSet.add(new Integer("3")); System.out.println("LinkedHashSet before removal : " + lhashSet); lhashSet.clear(); System.out.println("LinkedHashSet after removal : " + lhashSet); System.out.println("Is LinkedHashSet empty ? " + lhashSet.isEmpty()); }}
    • House Is Open For Queries