core java notes

8/8/2019 Core Java Notes

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Module-I

Java is a true object oriented language Every o o

programming language must satisfy three important features

like Encapsulation inheritance and polymorphism.

Encapsulation: is the of binding the data and methods

together into a single unit called class. The purpose of the

feature is more security to data and methods.

Inheritance: is the process by which the objects of one class

acquire the prosperities of objects of another class. Its

purpose is the reusability of data and methods.

Polymorphism: is the ability to take more than one form. It

is the process in which an interface with different method

implementory will be done. Its purpose is to reduce the code.

Benefits of oops:

OOP offers several advantages to both the programmer

and the user. The principle advantages are:-

1 Through inheritance, redundant code can be innovated

and the use of existing classes can be extended.2 The possibility of writing a body of cod once, and than

reusing that code over and over again. This leads to

saving of development time and higher productivity.

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3 Based on the objects work in a project can be

partitioned into different modules.

4The concept of data hiding helps to build secureprograms that can not be invaded by code in other parts

of the program.

5 Object oriented systems can be easily upgraded from

small to large systems.

6 Software complexity can be easily managed.

Dynamic Initialization of Variable:

Java allows variable to be initialized dynamically using any

expression valid at the time the variable in declared.

// dynamic initialization program.

Class dynamic

{ public static void main (String args [ ])

{ int a = 3, b = 4,

int c = math.sqrt(a*a + b*b); // dynamic

initialization.

System. out. println (c is+c) ;

}

}

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Control Statements:-

Control flow statements are used to make decisions

about which statements to execute and to otherwise change

the flow of execution in a program.

These are broadly of three types.

1. Selection Statements: if and switch (if else, nested if

else, else if ladder, nested switch)

2. Iteration (Looping) Statements: for, while, do while.

3. Jumping Statements:break, continue, return.

Static: It is a keyword applied to both variables and method.

These are called class members since both static variables

and static methods are accessed by the class name itself

without creating an object of a class.

These static variables are common to whole class

instead of a single object. Hence all objects of the class have

same constant value for a static variable. A static variable

may change but it is constant for whole class. It is same for

different objects of the same class.

Static methods can also be accessed without creating an

object of a class. main() method is a static method.

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They can not refer to this or super in any way.

final: final key word can be applied to variables, method

and classes. A final variable is one whose value does not

change during the execution of a program. A final class is

one, which cannot be extended; a final method is one, which

can not be overrided by its sub class.

this: It refers to the current object. this is used to avoid

hiding of instance variably by local variables.

Usage of super: The keyword super is used within methods

and usually in constructors of a derived class to refer to the

constructor of the class from which the new class was

derived .super refers to the super class.

Whenever a sub class needs to refer to its, immediate

super class, it can do so by the use of the key word super.

super has two general forms. The first call the super class

constructor. The second is used to access a members of the

super class that has been hidden by a members of sub class.

A sub class can call a constructor method defined by its super

class by use of the following form of super.

super (parameter list);

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Here parameter list specifies any parameters needed by the

constructor in the super class .super ( ) must always be the

first statement executed inside a sub class constructor. super

refers to the super class of the sub class in which it is used.

This has the general form. Super. members, here member can

be either a variable or a method.

Method overriding: When a method in a sub class has the

same name, same parameters and same return type as a

method in its super class,then the method in the subclass is

said to override the method in the super class. when an

overridden method is called from within a subclass, it will

always refer to the method defined by the sub class.

Method overriding is done in different classes. It leads

to polymorphism. Since the appropriate method is called at

run time, it is also called late-binding.

Abstract class: it is a class which may or may not contain

abstract and non-abstract methods. We cant create an object

of an abstract class.

When a class extends an abstract class it must

implement all the abstract methods or else the sub class it self

be declared as abstract.

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final: A final class is one, which can not be extended. The

execution of a final class is very fast since there is no

inheritance for a final class and hence there is no overriding

of methods.

Dynamic method Dispatch: Method overriding forms the

basis for one of Javas most powerful concept called

Dynamic method dispatch. Dynamic method dispatch is the

mechanism by which a call to an overridden method is

resolved at run time, rather than at compile time. This is

important because this is how Java implements run time

polymorphism.

Object class: It is the super class of all classes in Java.

Hence the methods in this class are overridden by its

subclasses. Some of the important methods in this class are

equals( ), finalize ( ), notify ( ), notify All ( ), to String (

), wait ( ) etc.,

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Importing a package :

A package in Java can be imported by using the key

word import

Eg:

import java.awt.*;

means all classes and interfaces in that package are available

to the given Java program

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Exception Handling

A Java exception is an object that describes an

exceptional condition that has occurred in a program.

Exceptions are the errors occurred at run time. By using

Exceptional handling we can make an abnormal program as a

normal program. Bu using exception handling we can predictthe flow of a program and can take necessary steps for its

normal flow.

The super class of all the exceptions is Throwable

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class. It has two subclass namely Error and Exception

classes. Error is the class which we cant avoid those errors

occurred at run time.

Exception is the class where we can handle those

errors.Exception has two sub classes namely Checked

exception and UncheckedException

Checked Exceptions: Those are the subclasses of the

Exception class. These are the errors occurred at run time

which can not be programmatically rectified.

Unchecked Exception: These are the errors occurred at run

time which can be programmatically rectified.

These are also called RunTimeExceptions.Most of the

exceptions are subclasses of RunTimeException class.

There are five key words used in Exception Handling of

Java. They are :

try

catch

finally

throw

throws

try:

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A try block is used to encapsulate a piece of code where

we may be expecting some run time errors.If this try block

finds any run time error,it throws those errors to a suitable

catch block.

If there is no run time error in the try block, then the

execution of the program is normal.

A try block must always be associated with atleast one catch

block or a finally block or both.

A try block may have multiple catch blocks, only one of

those multiple catch blocks will be executed.

catch :

The error thrown by a try block is caught in this catch

block.A catch block is always followed by a try block.

A catch block takes one parameter of type Exception

class.

If there are multiple catch blocks for a given try block,

the catch block which contains Super class Exception should

come after all sub class Exception catch blocks.

finally :

This finally block is used to execute whether an

Exception is caught or uncaught.

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This is followed by catch blocks or a simple try block.

This is mainly used to know the follow of execution of a

given program.

throw :

This is used to throw some predefined Exceptions

explicitly.It is mainly used to create User Defined

Exceptions.

throws :

This is used to throw Exceptions from methods.Most of

the checked exceptions use throws in Java programs.

Generally this is used while writing IO programs,JDBC

programs and other advanced Java Programs like Servlets,

RMI etc

Javas built in Exceptions :

There are many built in Exceptions in Java.These

are of type Exception and its sub class Exceptions.

Some of the important built in Exceptions in Exception

class are:

ArithmeticException

NumberFormatException

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ArrayIndexOutOfBoundsException

IndexOutOfBoundsException

IOException

InterruptedException etc

User Defined Exceptions :

In addition to built in Exceptions or predefined

Exceptions, we can create User Defined Exceptions also

depending upon the type of application.

User Defined Exception can be created by extending

Exception class.

Question: List out by an example the way to create user

defined exception (or) write a program to create user defined

exception.

Solution:

Generally user defined exceptions are used in practical

applications. All user defined exceptions extend Exception

class.

The following MyownException extends exception

class.

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// program to create user defined exception class named

//MyownException

//Program solution

class MyownException extends Exception

{

MyownException ( )

{ }

public String getMessage ( )

{

return in sufficient funds;

}

}

class Exceptiondemo

{

public static void main (String args [ ] )

{

try

{

int amount= Integer. parseInt(args [0]) ;

if (amount < 500)

{

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throw new MyownException ( );

}

}

catch (MyownException m )

{

System.out. println (m. getMessage ( ) ) ;

}

}

}

In the above program, the amount is entered from the

command line and if the amount is less than 500, it will

throw an user defined exception

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Multi Threading :Multi Threading is the concept used in Java based

on Multi tasking.Multi Threading is the technique used to

perform many things simultaneously. By using multithreading, we can make CPU more busy and hence reduce

the idle time of CPU.

Java Thread Model:

This model is also similar to process based multi

tasking. A Thread is a separate path of execution in a

program. In Multi Threading model of multi tasking all

thread have same address and are called light weight

components.Thread Priorities : Thread priorities are used by thread

scheduler to decide when each thread should be allowed to

run.These are the integer values.

There are three types of Thread priorities:

They are :

MIN_PRIORITY

MAX_PRIORITY

NORM_PRIORITY

MIN_PRIORITY........VALUE IS 1

MAX_PRIORITY........VALUE IS 10

NORM_PRIORITY........VALUE IS 5

Synchronization :

When two or more threads need access to a sharedresource,they need some way to ensure that the resource will

be used by only one thread at a time.This is called

Synchronization.

By using this, the code is safe and the resource is not

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corrupted. But the draw back is the execution is little bit

slow.

Creating a thread:

We can create our own thread by extending a Thread class or

implementing a Runnable interface.

Imp.methods in Thread class:

String getName(): Obtain thread's name

int getPriority(): Obtain a thread's priority.

boolean isAlive() : Determine if a thread is still running or

not

static void sleep(long milliseconds): suspend a thread for aperiod of time.

public void start() : Start a thread by calling it's run method.

Imp.methods in Runnable interface;

public void run() :this method must be implemented by

any class that implements this interface.

Creating Multiple Threads :

We can create multiple threads either by using a

Thread class or a Runnable interface.

Eg:

Creating three user defined threads Thread1,Thread2

and Thread3 by extending a Thread class;

//creation of multiple threads

class Thread1 extends Thread{}

class Thread2 extends Thread

{}

class Thread3 extends Thread

{}

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class Threaddemo

{

public static void main(String args[])

{

Thread1 t1=new Thread1();



}

}

Life cycle of a thread: In multithreading a thread is a

separate path of execution in a program. Every thread has 5

life cycle stages. They are:-

1.New born state

2.Runnable state

3.Running state

4.Blocked state

5. Dead state

A thread is in one of these five states .It can move from one

state to other state.

New born state: When a thread object is created the thread

is born and is said to be in new born state.

Runnable state: in this state, the thread is ready for

execution and is waiting for the availability of the processor.

Running state: Running means that the processor has given

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its time to the thread for its execution.

Blocked state: A thread is blocked when it is prevented from

entering into the runnable state and subsequently in the

running state. This happens when the thread is suspended,

sleeping or waiting in order to satisfy certain requirements.

Dead state: it is the last stage of a thread .A running thread

ends its life when it has completed executing its run ( )

method. It is a natural death.

Interthread Communication :

Inter thread communication in Java is done by means of three

methods.

They are wait(),notify() and notifyAll() methods.These

methods are called only from a synchronized method.

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String Handling

String is an array of characters in many programming

languages.In Java String is also an array of characters.

But mainly a String is a class in Java.It is a predefined class

in java.lang package.

Java.lang package is a default package in Java.

There are two String Handling classes available in Java

namely

String

StringBuffer

Both String and StringBuffer are final classes.

Both these classes are available in java.lang package.

String :

It is a final class in java.lang package.

A String class is an object in Java.A String is immutable, which means that it is fixed and the

contents of a String are always constant.

String constructors :

We can create an object of a String class by different ways

by using different types of constructors.

String s1=new String()

String s2=new String(program);

String s3=new String(s2);String s4=program;

char name[]={J,I,T,M};

String s5=new String(name);

There are many methods available in String class.

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Some of the important methods are:

length():

This method is used to find the length or size of a

String.This method returns number of characters present in

the given String.

Syntax of the method:

int length()

Eg:

String s=CoreJava;

int i=s.length();

length() returns the length of the string and its length is

stored in i which is 8concat():

This method is used to join or concat two strings.

The return type of this method is String.

This method takes one parameter which is also a String

String concat(String str)

Where str is the String joined to the given String.

Eg:

String s1=Java;

String s2=Program;

String s3=s1.concat(s2);

Where the output of s3 is JavaProgram

Concatenation operator(+):

The operator + is called a concatenation operator.

It is similar to concat() method.

In Java + is used to join any strings.Eg:

String s1=Java;

String s2=Program;

String s3=s1+s2;

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Where the output of s3 is JavaProgram

toLowerCase():

This method is used to convert upper case letters of a String

to lowercase.The return type of this method is String.

String toLowerCase()

Eg:

String s=JAVA PROGRAM;

The output of

s.toLowerCase() is java program

toUpperCase():

This method is used to convert lower case letters of a String

to uppercase.The return type of this method is String.String toUpperCase()

Eg:

String s= java;

The output of

s.toLowerCase() is JAVA

trim():

This method is used to filter white spaces before and after a

given String.

This mehod is not used to filter white spaces between any

two words of a String.

The return type of this method is String

String trim()

String s= Learn Java Basics ;

The output of

s.trim() is Learn JavaBasicsreplace():

This method is used to replace a given character of a String

with another new character . The return type of this method

is String.

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This method replaces the occurrence of the given character

through out the String by the new character.

String replace(char original,char new)

Eg:

String s=Liver;

The output of

s.replace(L,R) is River

String Comparision Methods:

There are three types of String Comparision in Java.

They are :

(i)equals()

(ii)==(iii)compareTo()

equals():

This method is used to compare actual contents of the two

strings.The return type of this method is a boolean value.

boolean equals(String s)

Eg:

String s1=new String(rama);

String s2=new String(jaya);


String s4=new String(RAMA);

The output of

if(s1.equals(s2)) is false


if(s1.equals(s3)) is true

equalsIgnoreCase():

This method is used to compare actual contents of the two

strings same as equals() except that it neglects case

sensitiveness of letters.

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Eg:


String s2=new String(RAMA);

The output of


if(s1.equalsIgnoreCase(s3)) is true

compareTo():

This method is used to compare two strings depending on the

ASCII values of the characters of the string.

The return type of this method is int.

int compareTo(String s)

Eg:String s1=A123;

String s2=C123;

String s3=A123;

It returns,

0 if s1 is greater than s2 and the output of

s2.compareTo(s1) is 2

=0 if s1 is equal to s2 and he output of

s1.compareTo(s3) is 0

Character Extraction:

The String class provides a number of ways in

which characters can be extracted from a String object.There

are many methods used to extract characters from a

String.The important method is charAt()charAt():

This method is used to extract a single character from a

String.The return type of this method is char.

char charAt(int where)

Here, where is the index of the character.

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Eg;

String s=ABCDEF;

s.charAt(2);

where the output is C,since at location 2 there is characterC.

Modifying a String:

There are many ways of modifying a String.Mostly

used modifying method is substring().

substring():

This method is used to return a substring of the given String

starting from the startindex of the given method.

The return type of this method is also a String.

This method is overloaded.(i)String substring(int startindex)

It returns a substring starting from startindex to the end of

the String.

Eg:

String s=Learn from the Basic Concepts;

012345---posions of characters in the String

The output of

s.substring(5) is from the Basic Concepts

(ii)String substring(int startindex,int endindex):

It returns a substring starting from startindex upto the end of

the end index without including endindex.

Eg:

String s=Learn from the Basic Concepts;

0123456789

s.substring(5,9) is fromIn this character in the location of 9 will not be included.

StringBuffer:It is a final class in java.lang package.

A StringBuffer is mutable,which means thatwhich means

that it is not fixed and the contents of a StringBuffer may

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change.It is dynamic in nature,where we can insert any

character at any location.

A StringBuffer class stores an additional memory for 16

characters.

There are some methods which are available only in

StringBuffer class only.Some of the important methods are:

capacity():

This method is used to return than memory

capacity of a StringBuffer.The return type of this method is

int.

Eg:StringBuffer sb1=new StringBuffer();

StringBuffer sb2=new StringBuffer(ABCDE);

Sb1.length() is 0 and sb2.length() is 5

sb1.capacity() is 16 where as

sb2.capacity is 21

append():

This method is similar to concat() method in

String class.This method is used to join any string to the

StringBuffer.

The return type of this method is StringBuffer.

StringBuffer append(String s)

Eg:

StringBuffer sb=new StringBuffer(Learn);

Sb.append(Basics);Where the output is LearnBasics

reverse():

This method is used to reverse the characters of a

given StringBuffer.The return type of this method is again a

StringBuffer.

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StringBuffer reverse()

Eg:

StringBuffer sb=new StringBuffer(ABCDEF);

sb.reverse();

Where the output is FEDCBA

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Exploring java.lang

java.lang package is the default package in Java

and it is automatically imported into all Java programs.There are many classes available in java.lang

package.Some of the important classes are :

Number

Math

ObjectRuntime

String

StringBuffer

System

Thread

ThreadGroup

Throwable

Some of the important interfaces are :

Cloneable

Comparable

Runnable

Simple Type Wrappers :

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Java uses simple data types like int,float,double,char etc

But these simple types are not objects. Java provides

Wrapper classes to convert simple types to objects.

Wrapper classes:In java all are objects except the primitive

data types.If we want to access primitive data types as

objects we should wrap the primitive data types within a

class.

There are 6 Wrapper classes.They are the sub classes of

Number.They are...

Double,Float,Byte,Short,Integer and Long.

Double d=12.33;

Double dd=new Double(d);

Int i=555;

Integet ii=new Integer(i);

float f=12.33f;

Float ff=new Float(f);

Runtime :

The Runtime class encapsulates the run-time

environment.We cannot instantiate a Runtime object.we can

get an object of Runtime class by calling method

Runtime.getRuntime();

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Memory Management:

Even though Java provides automatic garbage

collection,sometimes you will want to know how large the

object heap is and how much of it is left. To obtain these

values, use totalMemory() and freeMemory() methods

defined in Runtime class.

Object :

Object is the super class of all Java classes.

There are many methods available in Object class.

clone() method is used to create a duplicate copy of the

object on which it is called.Only classes that implements

Cloneable interface can be cloned. Cloneable interface

defines no members and it is a marker interface.

Thread :

A Thread is a predefined class in java.lang package. It is

a separate path of execution in a program.

Java uses Threads for implementing Multi Threading in

Java.By using a Thread we can create our own threads.

Runnable :

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This is an interface that must be implemented by any

class that will initiate a separate thread of

execution.Runnable defines one abstract method called,run(),

which is the entry point to the thread.

ThreadGroup :

A ThreadGroup is a class, which creates a group of

threads.This offer a convenient way to manage groups of

threads as a unit.

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Module-III

Java.util

It is the package which is mainly based on Collections.A Collection is a group of objects.Collection Frame work

standardises the way in which groups of objects are handled

by ur programs.These are available in java.util package.

Some imp. classes in java.util package.

ArrayList

HashMap

HashSetTreeSet

HashTable

LinkedList

StringTokenizer

Vector

Stack

Some imp. interfaces in java.util package are:

CollectionEnumeration

Iterator

List

Map

Set

Collection interface is the foundation upon which the

collections framework is built.A collection can not directly store values of type

int,char,double etc..If you want to

store such objects,you have to use primitive wrapers.

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List :The List interface extends Colletion and declares the

behavior of a collection that stores a sequence of elements.A

List may contain duplicate elements.

Set : A Set extends Collection and declares the behavior of a

collection that does not allow duplicate elements.

LinkedList:The LinkedList class extends

AbstractSequentialList and implements the List

interface.

ArrayList : ArrayList class extends AbstractList and

implements the List interface.ArrayList supports dynamic

arrays that can grow as needed.It can dynamically

increase or decrease in size.ArrayList are created with aninitial size.when this size is exceeded ,it is automatically

enlarged.When objects are removed,the array may be shrunk.

HashSet : HashSet extends AbstractSet and implements the

Set interface.In a HashSet the elements are not stored in a

sorted order.

TreeSet : TreeSet provides an information of the Set

interface that uses a tree for storage.

Objects are stored in sorted,ascending order.Access and

retrieval times are quite fast,which makes TreeSet an

excellent choice when storing large amounts of sorted

information that must be found quickly.

Iterator : An Iterator interface is used to cycle through the

elements in a collection.

This is also done by a ListIterator interface.Iterator enables

you to cycle through a collection,obtaining or removingelements.

ListIterator:

ListIterator extends Iterator to allow bidirectional traversal of

a list.

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Map : A Map interface is an object that stores associations

between keys and values or key/value pairs.Given a key we

can find its value.Both keys and values are objects.The

keysmust be unique,but the values may be duplicated.Some

may accept a null key and a null value.Map.Entry describes

an element(key/value pair)in a map.This is an inner class of

Map.

Enumeration : Enumeration interface defines the methods

by which you can enumerate(obtain one at a time)the

elements in a collection of objects.This is superceded by

Iterator.

Enumeration has two methods.boolean hasMoreElements()

Object nextElement()

Vector : Vector implements a dynamic array.It is similar to

ArrayList, but Vector vector is synchronised.A Vector

extends AbstractList and implements the List interface.

Stack : Stack is a subclass of Vector that implements a Last-

In,First-Out(LIFO) stack.

There are two opearation in Stack.Push n Pop operation.Push

operation adds an object to the

stack n Pop operation deletes an object from stack.

Dictionary : It is an abstract class that represents a key/value

pair like a Map.

HashTable : HashTable class is similar to a HashMap,but

HashTable is synchronized.

HashTable stores key/value pairs in a hash table.When usinga HashTable,you specify an object that is used as a key,and

the value that you want linked to that key.

StringTokenizer:It is mainly used for parsing.To use a

StringTokenizer,you specify an input string and a string that

contains Delimiters.Delimiters are characters that seperate

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tokens.Each character in the delimiters string is considered a

valid delimiter.For example ",;:"sets the delimiters to

comma,semicolon,and colon.

The Collection Algorithms:

The collections framework

Defines several algorithms that can be applied to collections

and maps.These algorithms are defined as static methods

within the Collections class.Several of the methods can throw

a ClassCastException,which occurs when an attempt is made

to compare incompatible types.

The Legacy classes and Interfaces:

Legacy classes and interfaces are sysnchronized.Butnone of the collection classes are synchronized.The legacy

classes defined by java.util package are

Dictionary

Hashtable

Properties

Stack

Vector

There is only one legacy interface called Enumeration

Random:

Random class is a generator of pseudorandom numbers.

Observable:

The Observable class is used to create sub classes that

other parts of your program can observe.When an object ofsuch a sub class undergoes a change, observing classes are

notified.

Observing classes must implement the Observer

interface, which defines the update() method.

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Java.iojava.io is a package in Java to perform input and output

operations.

Stream is an abstraction that either produces or consumesinformation.A stream is linked to a physical device by the

java i/o system.

System class defines three predefined stream variables

namely in,out,err

System.out refers to the standard output stream.By default,

this is the console.System.err refers to the standard error

stream,which is also the console by default.System.in refers

to standard input,which is the keyboard by default.Streams are two types.Byte streams and Character

streams.

(i)Byte Streams :

Byte streams provide a convenient means for handling

input and output of bytes. Byte streams are used when

reading or writing binary data.

Byte streams are defined by two classes namelyInputStream and OutputStream

(ii)Character Streams :

Character streams provide a convenient means for

handling input and output of characters.

Character streams are defined by two classes namely

Reader and Writer.

Serialization:

Serialization is the process of writing the state of an

object to a byte stream.This is useful when you want to save

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the state of your program to a persistent storage area, such as

a file.

Serialization is mainly needed to implement

Remote Method Invocation (RMI)

Serializable :

A Serializable is an interface.This interface has no

variables or methods. It is also called as Marker interface.

A Serialazable interface is used to make a class as

serialized.If a class is serialazable,all of its subclasses are

also serializable.

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Networking:

A network is a set of computers and peripherals, which are

physically connected together. Networking enables sharingof resources and communication. Internet is a network of

networks.

Java applets can be downloaded from a website. Networking

in java is possible through the use of java.net package.

Protocols: Communication between computers in a networkor a different networks require a certain set of rules called

protocol. Java networking is done using TCP/IP protocol.

Some of the different kinds of protocols available are HTTP,

FTP, SMTP.

HTTP: hyper text transfer protocol enables interaction with

the internet. It is the underlying protocol of www

FTP: file transfer protocol enables transfer of files between

computers.

SMTP: SimpleMailTransferProtocol is used to send email

between machines.

Client /Server: A computer which requests for some service

from another computer is called client. The one that

processes the request is called a server.

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Internet Address: Every computer connected to a network

has a unique IP address. An IP address is a 32- bit number

which has four numbers separated by period. A sample IP

address is given below.

80. 0 . 0 . 53

Domain Naming Service: it is very difficult to remember a

set of numbers (IP address) to connect to the internet .The

DomainNaming Service (DNS) is used to overcome this

problem. It maps one particular IP address to a string of

characters Eg: www.yahoo.com.

Port: It is a number given for a particular application

running in a system.

For a system there will be only one connection to

network, but there could be many applications running in the

system. So, for communicating with each of these

applications unique number is given. This number is known

as a port number.

Each port is identified by a number from 0 to 65, 535.

Each port can be allocated to a particular service port number

.7 is assigned for ECHO, 21 is assigned for FTP, 23 is for

Telnet, 25 is for e-mail, 80 for HTTP and 1099 for RMI

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registry.

Networking classes and interfaces: All these classes and

interfaces are contained in java.net package.

DatagramPacket,DatagramSocket,InetAddress,Socket,

ServerSocket, URL, URLConnection etc., are some of the

important classes in networking.

FileNameMap,SocketImplFactory, SocketOptions are

important interfaces in this networking.

Whois: It is a simple directory service protocol. It was

originally designed to keep track of administrators

responsible for internet hosts and domains.

A Whois client connects to one of several central

servers and requests directory information for a person or

persons. It can usually give you a phone number and an

e-mail address.

SocketBasics:

A socket is a connection between two hosts. It can

perform seven basic operations.

1.Connect to a remote machine.

2.Send data

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3.Receive data

4.Close a connection

5.Bind a port

6.Listen for incoming data

7.Accept connections from remote machines on the bound

port.

Javas Socket class, which is used by both clients and

servers, has methods that correspond to the first four of these

operations. The last three are needed only by servers which

wait for clients to connect to them. They are implemented by

the ServerSocket class.

Socket class is used to perform client side TCP

operations.

ServerSocket class contain every thing you need to write

servers in Java.

URL: is called as Uniform Resource Locator and is a

reference or an address to a resource on the internet.

A URL has two main components.

1. Protocol Identifier 2. Resource name.

Eg: The following is an example of a URL which addresses

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the java web site hosted by SunMicroSystem .

http://java.sun.com.

Protocol Identifier is http

Resource name is java.sun.com

URL Connection: it is a general purpose class for accessing

the attributes of a remote resource. Once you make a

connection to a remote server, you can use URLConnection

to inspect the prosperities of the remote object before

actually transporting it locally.

TCP (Transmission Control Protocol)

It is a connection based protocol that provides a reliable

flow of data between two computer, this is analogous to

making phone call. It provides point-to-point channel for

application that require reliable communication HTTP, FTP,

Telnet etc., are TCP protocols.

UDP (User Datagram protocol)

It is a connection less oriented protocol. It sends

independent packets of data from one computer to another

with no guarantees about arrival.This is analogous to sending

a letter through the postal service

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AppletAn Applet is a Java program which runs from a Java

enabled web browser.

It also runs by using an appletviewer which is a tool fromjdk(Java Development Kit)

Applet is a class in java.applet package.

Writing an Applet program:

We have to import two packages to write an Applet

Program.Those packages arejava.awt andjava.applet

There is no main() method in an Applet program.It has

an init() method where the execution of the Applet

begins.

We have to write an tag in order to see the

output of an Applet Program.

tag contains three mandatory attributes

namely code,width and height

We can use an tag in the same Java file where

your Applet program is written by commenting it.We

can also separately use this tag in a html file.Applet Architecture :

Applet is a window based program which runs by using

a Java compatible browser or an appletviewer. Its

architecture is different from a console based application

programs.

Applets are event driven.That is why we have to import

java.awt package also to write Applet programming. All

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Applets runs in a window. They have init() method instead of

main() as in console based programs.

Life cycle of an Applet:

There are four stages in the life cycle of an

Applet.These life cycle methods will be automatically

called by the container or browser where the Applet is

running.

The four life cycle methods are:

(i)init()

(ii)start()

(iii)stop()(iv)destroy()

init():

This is the first method called when an Applet is

initialized.This method is called exactly once.During this

method initialization of the Applet will generally be done.

start():

This is the next method called immediately called after the

init() method.This method will be called one or more

number of times.

stop():

This method is called when an Applet moves from one

page to another page.This method will also be called one

or more number of times.

destroy():

This is the last method called by an Applet.This method is

used to relieve the memory resources used by the

Applet.This method will also be called exactly once.

Applet Skeleton :

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There are five methods defiend in the skeleton of an

Applet. They are :

(i)init()

(ii)start()

(iii)stop()

(iv)destroy()

(v)paint()

The first four methods are also called life cycle methods

of an Applet.

paint() method is called when an Applets window must be

restored. In this method we can display any thing on the

Applet window.

This method is called when each time Applets output is

redrawn.

Note :

There are three interfaces in java.applet package.They

are AppletContext, AudioClip and AppletStub

AppletContext :

AppletContext is an interface that lets you get information

from the Applets execution environment.

The context of the currently executing Applet is obtained by

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a call to the getAppletContext() method defined in Applet

class.

showDocument()

Within an Applet,once you have obtained the Applets

context,you can bring another document into view by calling

showDocument() method. This method has no return values

and throws no exception if it fails.

Writing a SimpleApplet Program:

/*Writing SimpleApplet Program which displays a

message on the Applet window*/

import java.awt.*;

import java.applet.*;

/**/

public class SimpleApplet extends Applet{

public void paint(Graphics g)

{

g.drawString(Welcome to Applets,100,200);

}

}

Passing Parameters to Applets :

We can send parameters to Applet from a HTML file using

tag.A tag contains name and value as a

pair and by giving name we can get the value associated with

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that name.

getParameter() of Applet class is used to retrieve the value of

a given name in the tag.

/*Program in which a HTML file passes parameters to an

Applet and those values are displayed in the Applet

Window.*/

import java.awt.*;


/*

*/

public class ParamApplet extends Applet

{

Public void paint(Graphics g)

{

String s=getParameter(Company1);

g.drawString(s,200,300);

}

}

Explanation:

The output of the above program in an Applet window

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is Infosys

Note :

There are three interfaces in java.applet package.They

are AppletContext, AudioClip and AppletStub

AppletContext :

AppletContext is an interface that lets you get information

from the Applets execution environment.

The context of the currently executing Applet is obtained by

a call to the getAppletContext() method defined in Applet

class.

showDocument()

Within an Applet,once you have obtained the Applets

context,you can bring another document into view by calling

showDocument() method. This method has no return values

and throws no exception if it fails.

*********** E N D *********

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Event Handling

In AWT except Label component all other

components have Listeners.

Event Handling is the technique in which a given component

registers with a Listener and this Listener Handles the event

fired by that Component.

Event Handling Models:

Event Handling models are of two typesThey are :

Hierarchical Event Model

Delegation Event Model

Hierarchical Event Model:

In this type of model, the presentation logic and

business logic are not clearly separated from each other. This

method is now out dated.

Delegation Event Model :

In this type of model, the presentation logic and

business logic are clearly separated from each other.

Hence both presentation and Business logic are independent

of each other and the changes made in one logic has no effect

on other logic.

Event:

An event is an object that describes a state change in a

source.

An Action performed on a component is an Event.Some of

the activities that cause events to be generated are pressing

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a button,entering a character in a text field,selecting an

item in a choice,double clicking an item in a list,clicking

the mouse etc..

Event Source:

The Component on which the event has occurred is calledthe Event Source object.

Event class :

It is the class which is generated by the component

when Event Handling is done.

Suppose when a Button component is clicked,it generated

ActionEvent class.There are many types of Event classes available in

java.awt.event package.Some of the Event classes are:

Event ClassesActionEvent class is occurred

(i)When U click a button an Action Event occurs.(ii)Double clicking a List Item.

(iii)When U click a Menu Item.Adjustment Event class is occurred

When a Scrollbar is manipulatedTextEvent class is occurred

When U change the contents of the Text field or Textarea.

Item Event class is occurred

Generated when a check box or list item is clicked.It

also occurs when a choice selection is made.ComponentEvent class is occurred

Generated when a component ishidden,moved,resized,or becomes visible

ContainerEvent class is occurred

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When U Add a Component or Remove a Componentfrom a Container

FocusEvent class is occurred

When a component is receiving the focus and losingfocus.

WindowEvent class is occurred

Generated when a window isactivated,closed,deactivated,deiconified,iconified,

opened,or quitKeyEvent class is occurred

Generated when input is received from keyboard

MouseEvent class is occurredGenerated when the mouse is

dragged,moved,clicked,pressed,or released.It alsogenerated when the mouse enters or exits acomponent

Event Listener interface :

It is the listener which is registered with a given

component when an event occurs.

Suppose when a Button is clicked, ActionListener is

registered with it and the corresponding method of this

ActionListener interface to be implemented is

actionPerformed() method

Adapter Class:

An Adapter Class is a class that already implement all the

methods in its corresponding interface.

An Adapter class provides an empty implementation of allmethods in an event listener interface.Adapter classes are

used when only some of the events are to be received and

processed that are handled by a particular listener interface.

For example,MouseMotionAdapter class has two

methods.mouseDragged() and mouseMoved().The signatures

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of these empty methods are defined in the

MouseMotionListener interface.If only mouse dragged

events are to be performed then simply extend

MouseMotionAdapter and implement mouseDragged().The

empty implementation of mouseMoved() would handle the

mouse motion events.

Commonly used Adapter classes injava.awt.event package

and the interfaces are:

MouseAdapter class and the corresponding Listener

interface is MouseListener

MouseMotionAdapter class and the corresponding Listener

interface is MouseMotionListenerWindowAdapter class and the corresponding Listener

interface is WindowListener

********* E N D **********

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Module IV

AWT

AWT , Abstract Window Toolkit in Java is used to

write GUI programs.Today most of the front ends are

using Graphical User Interface(GUI) programming due to

many benefits such as user friendly,attractive,uses

different colors,uses many pictures,uses images,simulates

real world components etcJava provides powerful GUI programming by

using AWT.

The super class of all AWT components is Component.The

sub class of Component is Container.

Container has two sub classes namely Window and Panel

Window:

Window is the top level class which sits directlyon the desktop.It has again two sub classes namely Frame

and Dialog.

Frame:

It is the sub class of Window.A Frame contains

title,background,foreground,other controls like

minimize,maximize etc

Most of the AWT Programs are using a Frame window as

their container.The default Layout Manager of a Frame Window is a

BorderLayout.

The two important methods used in a Frame class are

void setSize(int width,int height)

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Font(String s,int style,int size)

Where s is the name of the Font like

TimesRoman,Sanserif,Monospaced etc

Where style is BOLD,ITALIC,PLAIN or combination

of styles and size is the size of Font

Eg:

Font f1=new Font(TimesRoman,Font.BOLD,40);

Font f2=new Font(Monospaced,Font.ITALIC,70);

Where f1,f2 are different objects of class Font

//Program working with Graphics by using Color and

Font classes.

import java.awt.*;


/**/

public class NameApplet extends Applet

{

public void paint(Graphics g)

{

Font f=new Font(TimesRoman,Font.BOLD,50);

g.setFont(f);

Color c=new Color(100,200,60);

g.setColor(c);

g.drawString(Working with Graphics,100,200);

}}

Controls used in AWT:

There are many controls used in AWT.

Some of the important controls used in AWT are

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Label

Button

Checkbox

Choice

List

TextField

TextArea

Except Label Component all other Components

have listeners.

Layout Managers :

It is essential to align the components properly in a

given Container.Alignment of Components is verydifficult .This difficulty is avoided by using a proper Layout

Manager.

There are many types of Layout managers used in

AWT.Some of the important Layout Managers are

(i)BorderLayout

(ii)FlowLayout

(iii)GridLayout

(iv)CardLayout

(v)GridbagLayout

Reflection:Reflection is the ability of a program to analyze itself. The

java.lang.reflect package provides the ability to obtain

information about the fields,constructors,methods, and

modifiers of a class.

Reflection is used to determine dynamically the

characteristics of a component

Remote Method Invocation(RMI) :

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Remote method invocation(RMI) is a distributed

application developed in Java.By using RMI, we can invoke

the method available in a remote machine.\

In RMI we have two machines where one machine acts

as a Server and another machine acts as a Client.

To run an RMI application, we have to start RMIRegistry

and we are using rmic compiler to create stubs and skeleton.

**************** E N D ********

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Swing Swing is an extension of AWT components in Java. Eventhough Java is platform independent language AWT

components are platform dependent.Hence the look and feelof AWT Components varies from one operating system to

other. Swing components are platform independent and hencelook and feel of these components is same on all operating

systems.In addition Swing includes have more features such

as TabbedPanes,Trees,Tables etc

In Swing the visible components starts with J and thesuper class of all components is JComponent.

Some of the important Components in Swing are

JLabel

JButton

JCheckBox

JRadioButton

JCombobox

JListJScrollPane

JTextField

JPassword

JTextArea

JOptionPane

JTable

JTree

JTabbedPane

NOTE:

We have to import java.awt and javax.swing package to write

Swing programs

All the above Swing Components extends JApplet.

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The main difference between Applet and JApplet is,in Applet

we are directly adding components to the Applet where as in

JApplet we are adding components to the ContentPane.

JApplet:Swing version of Applet.All swing visible

components extends JApplet

Icons and Labels:

InSwing,icons are encapsulated by the ImageIcon class.Two

of its constructors are

ImageIcon(String filename) where filename is the name of

the image

ImageIcon(URL url) where url is the location of the image.

JLabel:

We can create an object of a JLabel component by using the

constructor

JLabel() which is an empty constructor

JLabel(String s) where s is the name of the label

JTextField :

We can create an object of a TextField in swing by using the

constrcuctors

JTextField(int width) where width is the width of the text

field

JTextField(String s) where s is a String displayed in the text

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field.

JButton :

We can create an object of a Button in swing by using the

constructors

JButton() where it creates a button without any name

JButton(String s) where it creates a button where s is its

name

JComboBox :

It is similar to Choice in AWT.

We can create an object of a JComboBox by using its

default constructor.

JComboBox()

We can add item to the combo box by using

addItem(Object obj) method

TabbedPane :

It is a component that appears as a group of folders in a file

cabinet.Each folder has a title.When a user selects a folder,

its contents become visible.Only one of the folder is selected

at a time.Tabbed panes are generally used for configuration

options.

We can create an object of a Tabbed Pane by using the class

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JDBC(Java Data Base Connectivity)

Jdbc is a technology used to connect a Java program to any

data base.

We have to import java.sql package for writing JDBC

programs in Java

Types of Drivers used in JDBC :

There are four types of drivers supplied by Sun

Micro Systems to connect a Java Program to any data

base.

They are :

Type I:

JDBC-ODBC Bridge Driver

Type II

Native protocol partly Java Driver

Type III

Net protocol pure Java Driver

Type IV

Native protocol pure Java Driver

Above all Jdbc-Odbc Bridge Driver is the

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simplest Driver used to connect to any data base.

Steps in writing a JDBC program:

The following steps are followed while writing a JDBC

program.

Step 1:

Loading the driver.The statement used for this step is

Class.forName(sun.jdbc.odbc.JdbcOdbcDriver);

Step 2:Getting the Connection object

Connection

con=DriverManager.getConnection(jdbc:odbc:dsn,scott,

tiger); which is used to connect to Oracle data base

Step 3:Creating the Statement object

Statement st=con.createStatement();

Step 4:

Using the sql statements

int i=st.executeUpdate(CREATE TABLE ECEStudent(rnonumber,name varchar(10)));

/*Writng a JDBC program which is used to create a table

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catch(Exception e)

{

System.out.println(Error is +e);

}

}

}

**************** E N D ***********

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core java notes

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