the collection framework by kamalakar dandu

8/2/2019 The Collection Framework by Kamalakar Dandu

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The Collection Framework

Java.util package


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Java.util package contains a large assortment ofclasses and interfaces that support a board range offunctionality. For example. Java.util has classes

that generate random numbers, manage date andtime, observe events, manipulate sets of bits,tokenize strings and handle formatted data.

The java.util package also contains one of javas

most powerful subsystems: The CollectionsFramework. The collection framework issophisticated hierarchy of interfaces and classesthat provide state-of-the-art technology for

managing groups of objects. Because java.util contains a wide array of

functionality, it is quite large. There are 49 classesand 16 interfaces in java.util package.


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Collection Overview

The Java Collections Framework standardizes theway in which groups of objects are handled byyour programs. Collections were not part of theoriginal Java release, but were added by J2SE 1.2.Prior to the Collections Frameworks, Javaprovides ad hoc classes such as Dictionary,Vector, Stack and Properties to store and

manipulate groups of objects. But ad hoc approachwas not designed to be easily extended or adapted.Collection are an answer to this problems


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The Collection Interfaces

The collection Framework defines severalinterfaces. Beginning with the collection interfacesis necessary because they determine thefundamental nature of the collection classes.

List of interfaces:

Collection

List Queue(added by J2SE 5)

Set

SortedSet


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Set

Collection

List Queue

SortedSet

Collection : Enables you to work with group of objects; it is at the top of

the collection hierarchy.

List : Extends Collection to handle sequences(list of objects).

Queue : Extends Collection to handle special types of lists in whichelements are removed only from the head.

Set : Extends Collection to handle sets, which must contain unique

elements.

SortedSet : Extends Set to handle sorted sets.


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Collection Interface

The Collection interface is the foundation upon

which the Collections Framework is built because

it must be implemented by any class that defines acollection. Collection is a generic interface.

Collection declares the core methods that all

collections will have. These methods can throw

following Exception UnsupportedOperationException

ClassCastException


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Several of these methods can throw an

UnsupportedOperationException. This

occurs if a collection cannot be modified.

Collections that do not allow their

contents to be changed are called

unmodifiable. All the built-in collectionsare modifiable.

A ClassCastException is generated when object

is incompatible with another, such as when anattempt is made to add an incompatible object

to a collection.


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Methods of Collection interface

public boolean add(Object)public boolean addAll(Collection)

public boolean remove(Object)

public boolean removeAll(Collection)public void clear()

public int size()

public boolean isEmpty()public boolean contains(Object)

public boolean containsAll(Collection)

public boolean equals(Object)


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List Interface

The List interface extends Collection and declares

the behavior of a collectin that stores a sequence ofelements. Elements can be inserted or accessed bytheir position in the list, using zero-based index. AList may contain dulpicate elements.

In addition to the methods defined by Collection,List defines some of its own methods.Thesemethods will throwUnsupportedOperationException,

ClassCaseException and anIndexOutOfBoundsException

IndexOutOfBoundsException will raise when aninvalid index is used.


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Methods of List interface

public void add(int index, Object)

public void addAll(int index, Collection)

public int indexOf(object)

public int lastIndexOf(Object)

public Object get(int index)

public Object set(int index, Object)

public Object remove(int index)

public List subList(int start, int end)


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The Set interface

The Set interface defines a set. It extends

Collection and declares the behaviour of a

collection that does not allow duplicateelements. Therefore, the add() method

returns false if an attempt is made to add

duplicate elements to a set. It does notdefine any additional methods of its own.


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The SortedSet interface

The sortedSet interface extends Set and declaresthe behavior of a set sorted in ascending order.inaddition to those methods defined by Set, theSortedSet interface declares several methods.

These methods throw following exception NoSuchElementException

ClassCastException

NullPointerException

NoSuchElementException is thrown when no items arecontained in the invoking set.

NullPointerException is thrown if an attempt is made to

use a null object and a null is not allowed in the set.


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Methods of SortedSet interface

Public Object first()

Public Object last()

Public SortedSet headSet(Object end)

Public SortedSet tailSet(Object start)

Public SortedSet subSet(Object start, Object end)


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The Queue interface

The Queue interface was added by J2SE 5. It extends Collection

and declares the behavior of a queue, which is often a first-in,first-out list.

Despite its simplicity, queue offers several points of interest.

Elements can only removed from the head of the queue

There are two methods that obtain and remove

elements:pull() and remove(). The difference between themis that poll() returs null if the queue is empty, but remove()throw an exception.

There are two methods, element() and peek(), that obtain butdont remove the elements at the head of the queue. The

difference between them is that element() throws anexception if the queue is empty, but peek() returns null.

Offer() only attempts to add an elements to a queue. Becausesome queue have a fixed length and might be full, offer() canfail.


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Methods of Queue interface

public boolean offer(Object)

public Object element()

public Object peek()

public Object remove()

public Object poll()


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The Collection classes

ArrayList, LinkedList,AbstractList,AbstractSet,AbstractQue

ue, priorityQueue, HashSet, TreeSet

etc.


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The ArrayList class

The ArrayList class extends AbstractList andimplements the List interface.

ArrayList supports dynamic arrays that can growas needed. In java standard arays are of a fixedlength. After arrays are created, they can not grow.An ArrayList is a variable-length array of objectreferences. That is, an ArrayList can dynamicallyincrease or decrease in size.

ArrayList are created with an intial size. Whenthis size is exceeded, the collection isautomatically enlarged.


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The LinkedList class

The LinkedList class extends AbstractSequentialList and

implements the List and Queue interfaces. It provides alinked-list data structure.

In addition to the moethods that it inherits, the LinkedListclass defines some useful methods of its own formanipulating and accessing lists.

Public void addFirst(Object)

Public void addLast(Object)

Public Object getFirst()

Public Object getLast()

Public Object removeFirst()

Public Object removeLast()


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The Vector class

Vector implements a dynamic array. It is similarto ArrayList, but with two differences: Vector issynchronized, and it contains many legancymethods that are not part of the CollectionsFramework.

With the advent of collections, vector wasreengineered to extends AbstractList and toimplement the List interface.

In addition to the collections methods defined byList, Vector defines several legacy methods.


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Methods of Vector class

public void addElement(Object)

public Object elementAt(int index)

public Object firstElement()

public Object lastElement()

public int size()

public int indexOf(object element)

public int indexOf(Object element, int start)

public int lastIndexOf(Object element)

public int lastIndexOf(Object element, int start)

Public boolean is Empty()


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Public void setElementAt(Object element, int index)

Public void insertElementAt(Object element, int

index)

Public boolean contains(object element)

Public boolean removeElement(Object element)

Public void removeElementAt(int index)

public void removeAllElements()

Public boolean contains(Object element)

Public String toString()

Public void trimTosize()

Public boolean containsAll(Collection)


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The Date class

The Date class encapsulates the current date andtime. Its original version defined by java 1.0.When java 1.1 was released, many of the functionscarried out by the original Date class were moved

into the Calendar and DateFormat classes. Date supports the following constructors:

The processing of text often consist of parsing a formattedinput string. Parsing is the division of text into a set of

parts, or tokens. Date()

Date(long)

Date(int,int,int)

Date(int,int,int,int,int)


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Methods of Date class

Public int getDate()

Public int getYear()

Public int getMonth()

Public int getDay()

Public int getHours()

Public int getMinutes(0

Public int getSeconds()

Public long getTime()


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Public void setDate(int)

Public void setYear(int)

Public void setMonth(int)

Public void setHours(int)

Public void setMinutes(int)Public void setSeconds(int)

Public void setTime(long)

Public boolean before(Date date)Public boolen after(Date date)

Public boolean equals(Date date)


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StringTokenizer

The StringTokenizer class provides the first step in thisparsing process, often called the lexer or scanner.

StringTokenizer implements Enumeration interface

To use StringTokenizer, you specify an input string and astring that contains delimiters. Delimiters are characters

that separate tokens. For example, ,;: sets the delimiters to a comma,

semicolon and colon.

The default set of delimiters consists of the whitespacecharacters: space, tab, newline.

The StringTokenizer constructors are shown here: StringTokenizer(String str)

StringTokenizer(String str, String delimiters)


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Methods of StringTokenizer class

Public int countTokens()

Public boolean hasMoreElements()

Public boolean hasMoreTokens()

Public Object nextElement()

Public String nextToken()

Public String nextToken(String delimiters)


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Enumeration Interface

The Enumration interface defines themethods by which you can

enumerate(obtain one at a time) theelements in a collection of objects.

Enumration specifies the following twomethods

public boolean hasMoreElements()

public Object nextElement()


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Example of Enumeration

Vector v = new Vector();

v.addElement(1);

v.addElement(2);v.addElement(3);

System.out.println(v);

System.out.println(elements in vector :);

Enumeration ev = v.elements();

While(ev.hasMoreElement())

System.out.println(ev.nextElement());


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The Iterator interface

The Iterator interface defines the methods bywhich you can enumerate(obtain one at a time) theelements in a collection of objects.

Iterator enables you to cycle through a collection,obtaining or removing elements.

Iterator specifies the following three methods

public boolean hasNext() public Object next()

Public void remove()


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Example of Iterator with iterator()

Vector v = new Vector();

v.addElement(1);

v.addElement(2);v.addElement(3);

System.out.println(v);

System.out.println(elements in vector :);

Iterator iv = v.iterator();

While(iv.hasNext())

System.out.println(iv.next());


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Set classes HashSet classextends AbstractSet and

implements the Set interface. The elements are notstored in sorted order, and the output may very.

LinkedHashSet classextends HashSet.the outputwill be in the order in which the elements were

inserted. TreeSet classextends AbstractSet and

implements the Set and SortedSetinterface.Objects are stored in sorted, ascending

order. Access and retrieval times are quite fast,which makes TreeSet an excellent choice whenstoring large amount of sorted information thatmust be found quickly.


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The Map interfaces

A map is an object that stores associationsbetween keys and values, or key/values pairs.Given a key, you can find its value. Both keys and

values are objects. The keys must be unique, butthe values may be duplicated. Some maps canaccept a null key and null values, others cannot.

Map interfacemaps unique keys to values

Map.entry interfacedescribe an element in amap. This is an inner class of Map.

SortedMapextends Map so that the keys are

maintained in ascending order

the collection framework by kamalakar dandu

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