Introduction to Advance Java Concepts

Subject : Advance Java

Class : SYMCA

Subject Teacher : Dr. V. V Shaga

Unit-IObject Oriented Terminologies

Prepared By : Dr. V.V Shaga

Contents

• Classes & Objects• Methods & Overloading Methods• Constructors & Overloading Constructors• Using Object as Parameter• Returning Object• Static Variables & Methods• Command Line Arguments


What is a Class?

• A class is a blueprint/templates of objects.


•An object holds values for the variables defines in the class.•An object is called an instance of the Class•Everything in Java is an object• Real world Entity

Object life cycle:CreationUsageDestruction

What is an Object?


Object Creation

A variable s is declared to refer to the objects of type/class String:

String s;The value of s is null ; it does not yet refer to any object. A new String object is created in memory with initial “abc” value:

String s = new String(“abc”);Now s contains the address of this new object


Object Usage

Four usage scenarios: one variable, one object two variables, one object two variables, two objects one variable, two objects


Object Usageone variable, one object

String s = new String(“abc”);What can you do with the object addressed by s ?Example :

print the length: System.out.println(s.length() );


Object Usage

Two variable, one object

String s1 = new String(“abc”);String s2;Assignment copies the address, not value:

s2 = s1;Now s1 and s2 both refer to one object. After s1 = null; s2 still points to this object


Object Usage

Two variable, Two object

String s1 = new String(“abc”);String s2 = new String(“abc”);s1 and s2 objects have initially the same values:

s1.equals(s2) == trueBut they are not the same objects:

(s1 == s2) == falseThey can be changed independently of each other.


Object Usage

One variable, Two object

String s = new String(“abc”);s = new String(“xyz”);

The “abc” object is no longer accessible through any variable.


Example : Class & Object

A class with three variable members:class Box {

double width;double height;double depth;

}A new Box object is created and a new value assigned to its width variable:

Box myBox= new Box();myBox.width= 100;


Assignment

Create a Class Shape with attributes length,breadth,radius.Create objects rectangle and circle and set the values for the above attributes and display the area of both the shapes.


MethodsGeneral form of a method definition:

type name(parameter-list) {…return value; …}

Components:1) type : type of values returned by the method. If a method

does not return any value, its return type must be void.2)name : is the name of the method 3)parameter-list : is a sequence of type-identifier lists separated by commas4) return value indicates what value is returned by the method


Example for calling methodsWithin a class, we can refer directly to its member variables:

class Box { double width, height, depth; //Member variables void volume() //Member function or method { System.out.println(“Volume is :” + width* height * depth); }}


Example for calling methodsWhen an instance variable is accessed by code that is not part of the class in which that variable is defined, access must be done through an object:class BoxDemo{

public static void main(String args[]) {

Box mybox1 = new Box(); //creating instance of Boxmybox1.width = 10;mybox1.height = 20;mybox1.depth = 15; mybox1.volume(); //calling method of class

}}


Method Overloading

•It is legal for a class to have two or more methods with the same name.•However, Java has to be able to uniquely associate the invocation of a method with its definition relying on the number and types of arguments.•Therefore the same-named methods must be distinguished:

1) by the number of arguments, or2) by the types of arguments

Note : Overloading and inheritance are two ways to implement polymorphism


Constructors• A constructor initializes the instance variables of an object.• It is called immediately after the object is created but before

the new operator completes.– it is syntactically similar to a method– it has the same name as the name of its class– it is written without return type; the default return type of

a class constructor is the same class• When the class has no constructor, the default constructor

automatically initializes all its instance variables with zero.


Using Object as Parameter

void display(Test t) {

System.out.println("A="+t.a);System.out.println("B="+t.b);System.out.println("C="+t.c);

}public static void main(String args[])

{Test obj=new Test(2,3,4); obj.display(obj); // passing object as parameter

}


Returning Object

Test displayDetails(int a,int b,int c){ Test t=new Test();

t.a=a;t.b=b;t.c=c;return(t); //Returning Object ‘t’ in ‘newobj’

} public static void main(String args[])

{ Test obj=new Test(2,3,4); Test newobj;

newobj=obj.displayDetails(23,32,33);System.out.println(newobj.a + newobj.b +newobj.c);

}


Static Variables • It is a variable which belongs to the class and not to

object(instance)• Static variables are initialized only once , at the start

of the execution . • A single copy to be shared by all instances of the class• A static variable can be accessed directly by the class

name and doesn’t need any objectSyntax : <class-name>.<variable-name>


Static Methods

• It is a variable which belongs to the class and not to object(instance)

• A static method can access only static data. It can not access non-static data (instance variables)

• A static method can call only other static methods and can not call a non-static method from it.

• A static variable can be accessed directly by the class name and doesn’t need any object

Syntax : <class-name>.<method-name>


Command Line Arguments

• Command Line Arguments can be used to specify configuration information while launching your application.

• There is no restriction on the number of command line arguments. You can specify any number of arguments

• Information is passed as Strings.• They are captured into the String argument of

your main method


Command Line Argumentsclass Test{

public static void main(String b[]){System.out.println("Argument one = "+b[0]);System.out.println("Argument two = "+b[1]);}

}On Command Prompt:C:\>javac Test.javaC:\>java Test MCA STUDENTS


What is Inheritance?

• the ability of one class or object to possess characteristics and functionality of another class or object

• Advantages–Less duplication.–More generic code.–More robust design due to code reusability


Class Employee //Base or Parent or Super Class{string name;double wage;void incrementWage(){…}}

//Derived or Child or Sub class Class Manager extends Employee {string managedUnit;void changeUnit(){…}}

Manager m = new Manager(); //Creating instance of derived classm.incrementWage(); // inherited

Example


‘Super’ Keyword

“super” is a reference to the parent class or to access the members of the super class.Two Important uses:1) to access the hidden data variables of the

super class hidden by the sub class.2) is to call super class constructor in the

subclass


Accessing Variable of Super Classclass A{

int a; float b; void Show(){ System.out.println("b in super class: " + b); }}

class B extends A{ int a; float b; B( int p, float q){ a = p; super.b = q; // assigning value to super class variable } void Show(){ super.Show(); //calling super class method in derived class System.out.println("b in super class: " + super.b); System.out.println("a in sub class: " + a); } public static void main(String[] args){ B subobj = new B(1, 5); subobj.Show();}}


Calling Super Class Constructorclass A{

int a,b,c; A(int p, int q, int r){ a=p; b=q; c=r; } }

class B extends A{ int d; B(int l, int m, int n, int o){ super(l,m,n); // calling super class constructor d=o; } void Show(){ System.out.println("a = " + a + "b = " + b + "c = " + c + "d = " + d); } public static void main(String args[])

{ B b = new B(4,3,8,7); b.Show(); }

}


Method Overriding

• When method in a subclass has same name & type signature as method in its super class, then method in subclass is said to override the method in the super class.

• Overridden methods allow Java to support run-time polymorphism


Example

class ORDemo //Base Class{ int i,j; ORDemo(int x,int y) { i=x; j=y; } void show() //overridden method { System.out.println("super class values i & j=" + i + " " + j); }}

Cont…


Example

class MORDemo extends ORDemo{ int k; MORDemo(int x,int y,int z) { super(x,y); k=z; } void show() { //overriding method super.show(); System.out.println("derived class values k=" + k); } public static void main(String args[]) { MORDemo m=new MORDemo(1,2,3); m.show(); //this will call method of derived class } }


Assignment

• Write a program that creates a super class Figure that stores the dimensions of various two-dimensional objects. It also defines a method called area() that computes the area of an object. The program derives two subclasses from Figure. The first is Rectangle & the second is Triangle. Each of these subclasses overrides area() so that it returns the area of a Rectangle & a Triangle.


Rules for method overriding

1. The argument list should be exactly the same as that of the overridden method.

2. The return type should be the same or a subtype of the return type declared in the original overridden method in the super class.

3. The access level cannot be more restrictive than the overridden method's access level. For example: if the super class method is declared public then the overriding method in the sub class cannot be private . However the access level can be less restrictive than the overridden method's access level.

4. A method declared final cannot be overridden.

Cont…


6. A method declared static cannot be overridden but can be re-declared.

7. A subclass within the same package as the instance's superclass can override any superclass method that is not declared private or final.

8. A subclass in a different package can only override the non-final methods declared public or protected.

9. Constructors cannot be overridden.10. The overriding method can throw narrower or fewer

exceptions than the overridden method.

Rules for method overriding


Abstract class & methods

• super class cannot have any instance and such of classes are called abstract classes.

• Abstract classes usually contain abstract methods. Abstract method is a method signature (declaration) without implementation.


Example

public abstract class Player // class is abstract { private String name; public Player(String vname) { name=vname; } public String getName() // regular method { return (name); } public abstract void Play(); // abstract method: no implementation }

NOTE : Subclasses must override the method & provide its implementation If all the abstract methods of super class are not defined in this new class this class also will

become abstract


‘final’ Keyword

In Java programming the final key word is used for three purposes:

a. Making constants b. Preventing method to be overridden c. Preventing a class to be inherited


• The final keyword is a way of marking a variable as "read-only". Its value is set once and then cannot be changed.

For example, if year is declared as final int year = 2005; Variable year will be containing value 2005

and cannot take any other value after words.

‘final’ Keyword


‘final’ Keyword

• Prevents a method from being overridden• Example:

class A { final void show(){…. } }class B extends A{void show(){… // Compile time ERROR ! Can’t override}}


‘final’ Keyword

• Prevents a class from being inherited• Example:

final class A { //implicitly declares all of its methods as final

} }class B extends A{// ERROR ! Can’t inherit}


Packages

• A package is a collection of related classes and interfaces providing access protection and namespace management.


Types of Packages

• Pre-defined – java.lang.*(for achieving language functionalities)– java.io.*(for file handling operations)– java.applet.* (for browser oriented applications)– java.sql.* (for operations on databases)– java.text.*(for formatting date & time)– java.net.* (for client server applications)


Types of Packages

• User-defined : one which is developed by java Programmers

Syntax: keyword

package pack1[.pack2[.pack3….[.pack n…]];

Example:package P1;package P1.P2;


Steps for Developing Packages

1. Choose appropriate package name & package statement must be first executable statement

2. Choose appropriate class name whose modifier must be public

3. The modifier of Constructors & methods of a class must be public

4. Give the filename as class name with extension .java


Examplepackage tp; //package statement with package name tppublic class Test // class modifier public{ public Test() // constructor modifier public { System.out.println("Test - Default Constructor"); } public void show() // function modifier public { System.out.println("Test - Show function"); }}Note : for compiling packages use following on command prompt:

javac - d . Test.java This will create a .class file in ‘tp’ package.


Using package classes

import tp.Test; // import keyword for accessing classesclass PackDemo{ public static void main(String args[]) { Test t1=new Test(); t1.show(); }}


Interfaces

• An interface is like a class with nothing but abstract methods and final, static fields.

• All methods and fields of an interface must be public.

• As Java does not support multiple inheritance, interfaces are seen as the alternative of multiple inheritance, because of the feature that multiple interfaces can be implemented by a class.


Interface Declaration

interface Calculate { float pi=3.14f; //final and static by default double calculateArea(int r); }


Implementing Interface

class InterfaceDemo implements Calculate{ public double calculateArea(int r) { return (3.14*r*r); } public static void main(String args[]) { Calculate d= new InterfaceDemo(); System.out.println("Area is:"+d.calculateArea(4)); }}

Unit-1Exception Handling


Contents

• Exceptions• Exception Hierarchy• Types of Exception• Java Exception Handling• Using Try-Catch• Multiple Catch Blocks• Finally• throw and throws • User Defined (Custom) Exceptions


Exceptions

• An exception is an abnormal condition that arises in a code sequence at run time.

• In other words, an exception is a run-time error

• A Java exception is an object that describes an exceptional (that is, error) condition that has occurred in a piece of code


Exceptions

• When an exceptional condition arises, an object representing that exception is created and thrown in the method that caused the error


Exception HierarchyObject

Throwable

Exception

IOException

SQLException

RuntimeExceptio

nArithmeticException

NullPointerExceptio

nNumberFormatExceptio

n

Error


Types of Exceptions

Checked

• Extends Throwable Class except RuntimeExceptions and Errors

• Eg. IOException , SQLException

• Checked at Compile-time

Unchecked

• Extends RuntimeExceptions

• Eg. ArithematicException,NullPointerException,ArrayIndexOutOfBoundException

• Checked at runtime

Error

• Error is Irrecoverable• Eg.

OutOfMemoryError, VirtualMachineError etc


Examples of Exceptions1. int a=50/0; //ArithmeticException

2. String s=null; System.out.println(s.length());//NullPointerException

3. String s="abc"; int i=Integer.parseInt(s);//NumberFormatException

4. int a[]=new int[5]; a[10]=50; //ArrayIndexOutOfBoundsException

5. int num = s.nextInt(); Enter an Integer: abc // InputMismatchException


Java Exception Handling Keywords

There are 5 keywords used in java exception handling:– try– catch– finally– throw– throws


Using Try and Catch

Try•Java try block is used to enclose the code that might throw an exception. •It must be used within the method.•must be followed by either catch or finally block.

Catch•Java catch block is used to handle the Exception. •You can use multiple catch block with a single try.


Using Try and Catchpublic class TestTryCatch { public static void main(String args[]){ try{ int data=50/0; //throws exception }

catch(ArithmeticException e){System.out.println(e);}

} }


Internal working of Try-catch


Multiple catch blocks:

• You can have any number of catch blocks after a single try block.

• If an exception occurs in the guarded code the exception is passed to the first catch block in the list.

• If the exception type of exception, matches with the first catch block it gets caught, if not the exception is passed down to the next catch block.

• This continue until the exception is caught or falls through all catches.


Multiple catch blocks:public class TestMultipleCatchBlock {public static void main(String[] args) {

try {int a[] = new int[5];a[6] = 30 / 3;

}catch (ArithmeticException e) {

System.out.println("ArithmeticException");} catch (ArrayIndexOutOfBoundsException e) {

System.out.println("ArrayIndexOutOfBoundsException");}

System.out.println("Rest of the code...");} }

1

2


finally block

• Java finally block is a block that is used to execute important code such as closing connection, stream etc.

• Java finally block is always executed whether exception is handled or not.

• Java finally block must be followed by try or catch block.


finally blockclass TestFinallyBlock{ public static void main(String args[]){

try{ int data=25/5;

System.out.println(data); } catch(NullPointerException e) {

System.out.println(e);} finally {

System.out.println("finally block is always executed");}

System.out.println(“Rest of the code..."); } }


finally block


‘throw’ keyword

• The Java throw keyword is used to explicitly throw an exception.

• We can throw either checked or unchecked exception in java by throw keyword.

• The throw keyword is mainly used to throw custom exception.


‘throw’ keywordpublic class TestThrow1{ static void validate(int age){ if(age<18) throw new ArithmeticException("not valid"); else System.out.println("welcome to vote"); } public static void main(String args[]){ validate(13); } }


‘throws’ keyword• Any method capable of causing exceptions

must list all the exceptions possible during its execution, so that anyone calling that method gets a prior knowledge about

which exceptions to handle. • A method can do so by using the throws

keyword.


‘throws’ keywordclass Test {

static void check() throws ArithmeticException { System.out.println("Inside check function");

throw new ArithmeticException("demo"); }

public static void main(String args[]) {

try{ check(); } catch(ArithmeticException e) {

System.out.println("caught" + e); }

}}


User Defined Exceptions (Custom Exceptions)

• We can also create your own exception sub class simply by extending java Exception class.

• We can define a constructor for your Exception sub class (not compulsory) and you can override the toString() function to display your customized message on catch.



class MyException extends Exception{ String str1; MyException(String str2) { str1=str2; } public String toString(){ return ("Output String = "+str1) ; }}



class TestMultipleCatchBlock{ public static void main(String args[]){ try{ throw new MyException("My CustomException"); } catch(MyException exp){ System.out.println(exp) ; } }}

Unit – I

Serialization


Contents

• Serializable Keyword• Object Serialization


Serialization• Serialization is a process of converting an

object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams.

• The reverse process of creating object from sequence of bytes is called deserialization.

• A class must implement Serializable interface present in java.io package in order to serialize its object successfully.


Serialization

• Serializable is a marker interface (has no data member and method) that adds serializable behaviour to the class implementing it.

• Java provides Serializable API encapsulated under java.io package :– java.io.Serializable– java.io.Externalizable– ObjectInputStream– and ObjectOutputStream etc.


Object Serialization

• Object serialization is a mechanism where an object can be represented as a sequence of bytes that includes the object's data as well as information about the object's type and the types of data stored in the object.

• After a serialized object has been written into a file, it can be read from the file and deserialized that is, the type information and bytes that represent the object and its data can be used to recreate the object in memory.


Object Serialization


Object Serialization• The entire process is JVM independent, meaning

an object can be serialized on one platform and deserialized on an entirely different platform.

• Classes ObjectInputStream and ObjectOutputStream are high-level streams that contain the methods for serializing and deserializing an object.

NOTE : Static members are never serialized because they are

connected to class not object of class.


Serializing ObjectStudentInfo.java

import java.io.*;public class StudentInfo implements

Serializable {

int roll;String name;

StudentInfo(int r,String n){this.roll=r;this.name=n;

}}


Serializing ObjectTestStudentInfo.java

import java.io.*;

public class TestStudentInfo {public static void main(String[] args) {

StudentInfo obj=new StudentInfo(10,"Vikrant");try{FileOutputStream fos=new FileOutputStream("Viks.txt");ObjectOutputStream oos=new ObjectOutputStream(fos);oos.writeObject(obj); // writing object to fileoos.close();fos.close();}catch(Exception ex){System.out.println(ex);}

}


Deserialization of ObjectTestStudentInfo.javaimport java.io.*;public class TestStudentInfo {public static void main(String[] args) {

StudentInfo si=null ; try { FileInputStream fis = new FileInputStream("Viks.txt"); ObjectInputStream ois = new ObjectInputStream(fis);

si = (StudentInfo)ois.readObject(); // Deserialization of Object } catch (Exception e) { System.out.println(e); } System.out.println(si.roll); System.out. println(si.name);}


Why to Serialize?

The Objects can be Serialized to achieve following : To save objects into file at the time of execution To read and write later in the same application Transmit object over a network To support persistence in java objects Maintain the java objects type and safety properties in

serialized form To communicate via sockets or Remote Method

Invocation (RMI) To implement java beans


Questions1. What is Serialization ? What we can achieve by

Serializing the Object?2. What is object stream? Explain different types of

object streams.3. List out the different methods of

ObjectOutputStream.4. What are the steps involved in serialization?5. WAP to serialize the object employee whose instance

variable are emp_code and emp_name . There are atleast 5 records of employee are expected. In the same program deserialize the object.


References

• http://www.studytonight.com• http://www.javatpoint.com• https://www.tutorialspoint.com/

http://www.studytonight.com/

http://www.javatpoint.com/

https://www.tutorialspoint.com/


Fill in the blanks

A) The path travelled by data in a program is known as __________________

B) The ability of an object to record its state so that it can be reproduced in future is called___________________

C) The class which is responsible for reading objects from stream is __________________

Unit – I

JDBC(Java Database Connectivity)


Contents

• Introduction to JDBC• JDBC Architecture• JDBC Drivers• Steps to Create JDBC Application• Operations– Insert– Update– Delete– Select


JDBC (Java Database Connectivity)

• JDBC is Java application programming interface (API) that allows the Java programmers to access database management system from Java code

• defines interfaces and classes for writing database applications in Java by making database connections.

• executing SQL statements and supports basic SQL functionality.

• It provides RDBMS access by allowing you to embed SQL inside Java code.


JDBC Architecture

Application JDBC Driver

• Java code calls JDBC library• JDBC loads a driver • Driver talks to a particular database• Can have more than one driver -> more than one

database• Ideal: can change database engines without changing

any application code


JDBC Drivers

JDBC

Type I“Bridge”

Type II“Native”

Type III“Middleware”

Type IV“Pure”

ODBC ODBCDriver

CLI (.lib)

MiddlewareServer


Type I Drivers

• Use bridging technology• Requires installation/configuration on client

machines• Not good for Web• e.g. ODBC Bridge


Type II Drivers

• Native API drivers• Requires installation/configuration on client

machines• Used to leverage existing libraries• Usually not thread-safe• Mostly out-dated now• e.g. Intersolv Oracle Driver, WebLogic drivers


Type III Drivers

• Calls middleware server, usually on database host

• Very flexible -- allows access to multiple databases using one driver

• Only need to download one driver• But it’s another server application to install

and maintain• e.g. Symantec DBAnywhere


Type IV Drivers

• 100% Pure Java• Use Java networking libraries to talk directly

to database engines• Only disadvantage: need to download a

new driver for each database engine• e.g. Oracle, mySQL


Steps for Creating JDBC Application

1.Establish a Connection2.Create JDBC Statements3.Execute SQL Statements4.GET ResultSet 5.Close connections


1. Establish a connection

• import java.sql.*;• Load the vendor specific driver

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");// Dynamically loads a driver class for databases

• Make the connection Connection con = DriverManager.getConnection(“jdbc:odbc:DSNName”,

"","");// Establishes connection to database by obtaining

a Connection object


2. Create JDBC statement(s)

Three kinds of Statements:

Statement: Execute simple sql queries without parameters.Statement st= con.createStatement() ; Creates an SQL Statement object.

Prepared Statement: Execute precompiled SQL queries with or without parameters.PreparedStatement objects are precompiled SQL statements.Ex:PreparedStatement ps=con.prepareStatement("insert into Student values(?,?,?,?)")

Callable Statement: Execute a call to a database stored procedure.CallableStatement cs=con.prepareCall(String sql)returns a new CallableStatement object. CallableStatement objects are SQL stored procedure call statements.


3)Executing SQL Statements

String insertStud = "Insert into Student values (1,’Vikrant’,’Pune’)";

st.executeUpdate(insertStud );


4) Get ResultSet

String query = "select * from Student";

ResultSet rs = st.executeQuery(query);

while ( rs.next() ){

System.out.println(rs.getInt(1) + " " + rs.getString(2)+ “ ” + rs.getString(3));}


5) Close connection

st.close();con.close();


Sample JDBC Program// for insertion of recordsimport java.sql.*;public class Employee {

static Connection con=null;static PreparedStatement pst=null;static String username="postgres";static String pwd="root";static String

connURL="jdbc:postgresql://localhost:5433/postgres";public static void main(String[] args) {try{//loading the driversClass.forName("org.postgresql.Driver");

//Establish the connection

con=DriverManager.getConnection(connURL,username,pwd);pst=con.prepareStatement("insert into employee

values(?,?)");


Sample JDBC Program

pst.setInt(1, 1009);pst.setString(2, "G.D Agrawal");//Executing the SQL statementint x=pst.executeUpdate();System.out.println( x +" Record inserted..");//Close the Connectionscon.close();

}catch(Exception ex) {

System.out.println(ex);}

}}

Unit-1Collections


Contents

• Collections• Collection Interface• Types of Collections– Set– List– Queue


Collections

• Collections is a group of objects which could be homogenous or heterogeneous with some size.

• Collections in Java are data-structures primarily defined through a set of classes and interface

• It is also refer to as a container which contains the group of multiple elements into a single unit.


Collections

• Collections are used :– To generalize the array concept– To store multiple types of objects– Resizable– To define set of interfaces for storing java objects

• So collection is a group of classes which gives the functionality of managing : Vectors, ArrayList, HashMap, LinkedList, Stack and Hashtable.


Collection Interface • Collection Interface uses following methods :– add() – to add element in collection– remove()- to remove element from collection– toArray() - convert collection into array of elements– contains() - to check if a specified element is in the

collection respectively.• Collection Interface is a sub-interface of Iterator

Interface. The Iterator interface provides the iterator() method that goes through all of the elements in the collection.


Types of CollectionsTypes of Collection

Sets

HashSet

TreeSet

LinkedHashSet

Lists

ArrayList

LinkedList

Vector

Queue


Set Interface

Types of Collections

Extends collection interface• Doesn’t allow duplicate elements• Supports all methods present in collection

interface Method Description

boolean add(Object element) It returns false if element already present in Set

boolean addAll(Collection c) If all the elements of specified collection are part of set, it returns false


Set Interface


Set Interface:

HashSet class

•Implemented using a hash table•No ordering of elements.•add, remove, and contains methods constant time complexity O(c)

TreeSet class•Implemented using a tree structure.•Guarantees ordering of elements.•add, remove, and contains methods logarithmic time complexity O(log (n)), where n is the number of elements in the set.


Set InterfaceTypes of Collections

LinkedHashSet class

•Subclass of HashSet•Maintains Doubly linked list of the entries in the set•Fixed order but not sorted manner•Both HashSet and LinkedHashSet have the same constructor


Set InterfaceTypes of Collections

import java.util.*;public class TestHashSet {public static void main(String[] args) {

HashSet obj=new HashSet();obj.add("A");obj.add("B");obj.add("C");obj.add("A");System.out.println(obj+"\n");System.out.println("Size :" + obj.size());}}

OUTPUT:

[A, B, C]

Size :3



List Interface: ( List is ordered collection called as sequence ) .

• ArrayList and LinkedList are implementation classes of List interface.

• Extends collection interface• May have duplicate elements• Elements in list Indexed from 0 to list.size• Elements added at the end of list.• After removing nth element , all next elements shifted

one position up


Types of Collections Method Description

boolean add(Object element)void add (int index,Object element)

Ensures collection contains the specified element. If index given then element added at specified index otherwise at the end of list

boolean addAll(Collection c)boolean addAll(int index , Collection c)

Inserts all the elements from specified collection into this collection. If index is supplied , then position is selected for insertion. Else at the end inserted

List Interface


Types of Collections Method Description

boolean get(int index) Return the indexth entry in the list

boolean remove(Object element)Object remove(int index)

Removes element from collection. We can remove element of specified index number. First method with Boolean returntype returns the value indicating whether element was removed or not

List Interface



List Interface

ArrayList class•ArrayList is an array based implementation where elements can be accessed directly via the get and set methods.•Can be dynamically increase or decrease•Three Constructors:•ArrayList() , •ArrayList(Collection C),•ArrayList(int initialcapacity)

LinkedList class

•Gives better performance on add and remove compared to ArrayList.•Gives poorer performance on get and set methods compared to ArrayList .



Queue Interface:• Queue is a collection used to hold multiple

elements prior to processing. • Besides basic Collection operations, a Queue

provides additional insertion, extraction, and inspection operations.

• Order elements in a FIFO (first-in, first-out) manner

• In a FIFO queue, all new elements are inserted at the tail of the queue.


Collection Framework

• Collection Framework is the unified architecture that represent and manipulate collections.

• The collection framework provides a standard common programming interface to many of the most common abstraction without burdening the programmer with many procedures and interfaces.

• It provides a system for organizing and handling collections.


Collection Framework

This framework is based on:– Interfaces that categorize common collection

types.– Classes which proves implementations of the

Interfaces.– Algorithms which proves data and behaviors need

when using collections i.e. search, sort, iterate etc.


Hierarchical representation of Interfaces in Collection

Framework

Collection

List Set

SortedSet

Map

SortedMap

Education

Introduction to Advance Java Concepts