Core Java Notes

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. 1

3 Based on the objects work in a project can be partitioned into different modules. 4 The concept of data hiding helps to build secure programs 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) ; } }

2

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.

3

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);

4

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 can’t 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.

5

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 Java’s 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 ( ), ), wait ( ) etc., **********

E

N

D

*********

6

to String (

Module – II Packages and Interfaces A Package in Java is one which contains classes and interfaces.There are many packages used in Java. Java.lang is the default package in Java. Some of the important packages in Java are : java.io java.net java.util java.awt java.awt.event java.applet java.sql javax.swing Access Specifiers: A modifier assigns characteristics to the method.That is it specifies the availability of the method to the other methods or classes.Similarly you can have specifiers for packages and interfaces. They are : private public protected default 7

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 *********************

E

N

D

**********

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 predict the flow of a program and can take necessary steps for its normal flow. The super class of all the exceptions 8

is Throwable

class. It has two subclass namely Error and Exception classes. Error is the class which we can’t 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:

9

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.

10

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…

Java’s 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

11

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. 12

// 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) {

13

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 *********

E

N

14

D

*********

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 multi threading, 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 shared resource,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 15

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 a period 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 {} 16

class Threaddemo { public static void main(String args[]) { Thread1 t1=new Thread1(); Thread1 t2=new Thread2(); Thread1 t3=new Thread3(); } } 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 17

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.

**************

E

N

D

18

**************

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. 19

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 8 concat(): 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; 20

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 JavaBasics replace(): This method is used to replace a given character of a String with another new character . The return type of this method is String.

21

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 s3=new String(“rama”); String s4=new String(“RAMA”); The output of if(s1.equals(s2)) is false if(s1.equals(s4)) 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. 22

Eg: String s1=new String(“rama”); String s2=new String(“RAMA”); The output of if(s1.equals(s2)) is false 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. 23

Eg; String s=”ABCDEF”; s.charAt(2); where the output is C,since at location 2 there is character C. 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 from In 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 that which means that it is not fixed and the contents of a StringBuffer may

24

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. 25

StringBuffer reverse() Eg: StringBuffer sb=new StringBuffer(“ABCDEF”); sb.reverse(); Where the output is FEDCBA

******* E

N

D

26

**********

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 Object Runtime String StringBuffer System Thread ThreadGroup Throwable Some of the important interfaces are : Cloneable Comparable Runnable Simple Type Wrappers :

27

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();

28

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 :

29

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.

**************

E

N

30

D

*********

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 HashSet TreeSet HashTable LinkedList StringTokenizer Vector Stack Some imp. interfaces in java.util package are: Collection Enumeration 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.

31

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 an initial 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 removing elements. ListIterator: ListIterator extends Iterator to allow bidirectional traversal of a list. 32

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 LastIn,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 using a 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 33

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.But none 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 of such a sub class undergoes a change, observing classes are notified. Observing classes must implement the Observer interface, which defines the update() method.

34

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

35

Java.io java.io is a package in Java to perform input and output operations. Stream is an abstraction that either produces or consumes information.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 namely InputStream 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 36

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.

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

37

Networking: A network is a set of computers and peripherals, which are physically connected together. Networking enables sharing of 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 network or 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.

38

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

39

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

40

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. Java’s 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

41

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

42

postal

service

DatagramPacket,DatagramSocket

etc.,

are

UDP

type

connection less protocols. Differencec Between TCP n UDP TCP UDP It is a connection oriented It is a connectionless oriented protocol protocol It is similar to Telephone It is similar to sending letter from Post office Overheads are high Overheads are low HTTP,FTP,SMTP etc… DatagramPacket,DatagramSocket are Connection oriented etc…are Connectionless oriented protocols protocols It is more reliable Less reliable Order guaranteed

Order of deliver not guaranteed

Delivery guaranteed

Delivery not guaranteed

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

43

Applet An Applet is a Java program which runs from a Java enabled web browser. It also runs by using an appletviewer which is a tool from jdk(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 are java.awt and java.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. It’s 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 44

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 : 45

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 Applet’s window must be restored. In this method we can display any thing on the Applet window. This method is called when each time Applet’s 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 Applet’s execution environment. The context of the currently executing Applet is obtained by

46

a call to the getAppletContext() method defined in Applet class. showDocument() Within an Applet,once you have obtained the Applet’s 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

47

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.*; import java.applet.*; /* */ 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

48

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 Applet’s 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 Applet’s 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

49

*********

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 types They 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 50

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 called the 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 Classes ActionEvent 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 manipulated TextEvent class is occurred When U change the contents of the Text field or Text area. 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 is hidden,moved,resized,or becomes visible ContainerEvent class is occurred 51

When U Add a Component or Remove a Component from a Container FocusEvent class is occurred When a component is receiving the focus and losing focus. WindowEvent class is occurred Generated when a window is activated,closed,deactivated,deiconified,iconified, opened,or quit KeyEvent class is occurred Generated when input is received from keyboard MouseEvent class is occurred Generated when the mouse is dragged,moved,clicked,pressed,or released.It also generated when the mouse enters or exits a component 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 all methods 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 52

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 in java.awt.event package and the interfaces are: MouseAdapter class and the corresponding Listener interface is MouseListener MouseMotionAdapter class and the corresponding Listener interface is MouseMotionListener WindowAdapter class and the corresponding Listener interface is WindowListener

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

53

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 etc… Java 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 directly on 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) 54

where width and height are the dimensions of the Frame in pixels. void setVissible(boolen b) where b is a boolean data type and the Frame window will be visible if boolean value is true Panel : A Panel is a super class of Applet. Generally a Panel is used as a subcontainer of componenets. The default Layout Manager of a Panel and Applet is a FlowLayout Creating a Frame Window: We can create a Frame Window by importing java.awt package and extending a Frame class. //Sample Frame Window program import java.awt.*; class MyFrame extends Frame { public static void main(String args[]) { MyFrame mf=new MyFrame(); Mf.setTitle(“Frame Window Example”); mf.setSize(200,300); mf.setVisible(true); } } Explanation: The above program creates a Frame Window with title name as Frame Window Example with pixels as 200 and 300. Working with Graphics:

55

Graphics is a class available in java.awt package.There are many methods available in Graphics class.This Graphics class is used to display anything on the Frame or Applet Window by using the method called paint() method. Syntax of a paint() method: public void paint(Graphics g) There are many methods available in Graphics class. void drawstring() is used to display any String or Message on the Applet or Frame window. We can use Color and Font classes in Graphics class. Color and Font are also the predefined classes in java.awt package. Color: It is class in java.awt package. We can create an object of a Color class by using the constructor Color(int red,int green, int blue) Where red,green and blue are the integer values lies between 0 and 255. Eg: Color c1=new Color(0,0,0); Color c2=new Color(255,255,255); Color c3=new Color(100,50,200); Color c4=new Color(20,100,240); Where c1,c2,c3 and c4 are different Colors. Font: It is another class in java.awt package. We can create an object of a Font class by using the constructor 56

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.*; import java.applet.*; /**/ 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 57

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 very difficult .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) :

58

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

59

********

Swing Swing is an extension of AWT components in Java. Even though Java is platform independent language AWT components are platform dependent.Hence the look and feel of AWT Components varies from one operating system to other. Swing components are platform independent and hence look 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 the super class of all components is JComponent. Some of the important Components in Swing are JLabel JButton JCheckBox JRadioButton JCombobox JList JScrollPane 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. 60

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

61

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 it’s name JComboBox : It is similar to Choice in AWT. We can create an object of a JComboBox by using it’s 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

62

default constructor of JTabbedPane class ScrollPane: ScrollPane is a component that presents a rectangular area in which a component may be viewed.Horizontal and /or vertical scroll bars may be provided if necessary. We can create aa object by using a default constructor JScrollPane() Tree: A Tree is a component that presents a hierarchical view of data.A user has the ability to expand or collapse individual subtrees in this display. A Tree in swing is obtained by extending JTree which extends JComponent Table : Table is a component that displays rows and columns of data.You can drag the cursor on column boundaries to resize columns. We can create a Table in swing by extending JTable which extends JComponent. ************

E

N

D

63

*********

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

64

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(rno number,name varchar(10))”); /*Writng a JDBC program which is used to create a table 65

ECEStudent and enter any two values */ import java.sql.*; class Jdbcprogram { public static void main(String args[]) { try { Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”); Connection con=DriverManager.getConnection(“jdbc:odbc:dsn”,”scott”, ”tiger”); Statement st=con.createStatement(); int i=st.executeUpdate(“CREATE table ECEStudent(rno number,name varchar(10))”); int

j=st.executeUpdate(“INSERT

into

ECEStudent

into

ECEStudent

values(111,’xyz’); int

k=st.executeUpdate(“INSERT

values(222,’abc’); System.out.println(“Your operation is successfully done”); }

66

catch(Exception e) { System.out.println(“Error is “+e); } } }

**************** E

N

D

67

***********

68