Introduction to JAVA1

8/7/2019 Introduction to JAVA1

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JAVA MIND BENDER JAVA

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A.B.COLLEGE PATHANKOT

Introduction to JAVA

Introduction:

Java is a general purpose, object-oriented programming language

introduced by Sun Microsystems of USA in 1991.Originally called Oak

by James Gosling, one of the inventors of the language. The java team

which included Patrick Naughton discovered that the existing languages

like c and c++ had limitations in terms of both reliability and portability.

They modelled their new language java on C and C++ but removed a

number of features of C and C++ that were considered as sources of

problems and thus made Java is really simple, reliable, portable, simple,

compact, interactive and powerful language. The most striking feature of

the language is that it is a platform neutral Language. Java is the first

language that is not tied to any particular hardware or operating system.

Programs developed in java can be executed anywhere on any system.

JAVA Features:

1.Compiled and Interpreted: - Java combines both theseapproaches thus making java a two stage systems. First, java compiler

translates source code into what is known as bytecode instructions.

Second, java interpreter generates machine code that can be directly

executed by the machine that is running the java programs.


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2.Platform-independent and portable: - The most significantcontribution of java over other language is its portability. Java

programs can be easily moved from one computer system to another,

anywhere and anytime.

3.Object-Oriented: - Java is a true object-oriented language. Almosteverything in java is an object. All program code and data reside

within objects and classes. The object model in java is simple and

easy to extend.

4.Robust and secure: -Java is a robust language. It provides manysafeguards to ensure reliable code. It has strict compile time and run

time checking for data types. Security becomes an important issue for

a language that is used for programming on internet.

5.Distributed: - Java is designed as a distributed language. It has theability to share both data and programs. This enables multiple

programmers at multiple remote locations to collaborate and work

together on a single project.

6.Multithreaded: - Multithreaded means handling multiple taskssimultaneously. Java supports multithreaded programs. This means

we need not wait for the application to finish one task before

beginning another.

7.Dynamic and Extensible: - Java is a dynamic language. Java iscapable of dynamically linking in new class libraries, methods and


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objects. Java programs support functions in other languages such as C

and C++. These are native methods.

Object-Oriented Programming (OOP):

Object-Oriented Programming (OOP) is an approach to perform

organization and development, which attempts to eliminate some of

the pitfalls of conventional programming methods by incorporating

the best of structured programming feature with several new

concepts. Object-Oriented Programming is an approach that

provides a way of modularizing programs by creating partitioned

memory area for both data and function that can be used as

templates for creating copies of such modules on demand. OOP

treats data as a critical element in the program development and does

not allow it to flow freely around the system.


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Basic Concepts ofOOP:

y Objects and Classes: - Objects are the basics runtimeentities in an object-oriented system. They may represent a

person, a place, a bank account, a table of data or any item that

the program may handle. They may also represent user-defined

data types such as vectors and lists. Any programming problem is

analyzed in terms of objects and the nature of communication

between them.

A class may be thought of as a data types and an object as a variable

of that data type. Once a class has been defined, we can create any

number of objects belonging to that class. A class is thus a collection of

objects of similar type.

yEncapsulation: - The wrapping up of data and methods

into a single unit (called class) is known as encapsulation. The

data is not accessible to the outside world and only those

methods, which are wrapped in the class, can access it.

Encapsulation makes it possible for objects to be treated like

black boxes, each performing a specific task.

y Inheritance: -Inheritance is the process by which objects ofone class acquire the properties of objects of another class. The

concepts of inheritance provide the idea of reusability. This


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means that we can add additional features to an existing class

without modifying it.

y Polymorphism:- Polymorphism means the ability to takemore than one form. It plays an important role in allowing objects

having different internal structures to share the same external

interface. It is extensively used in implementing inheritance.

The JAVA Abstract Window Toolkit (AWT)Package:

Java applets are run in a web browser this makes them different from a

standalone java program. Both a Web Browser and JDKs Applet

Viewer can be used to run a java Applet. To display data within a GUI,

an applet must use java classes specifically designed for displaying

information in a GUI environment. The java GUI classes are containedinjava.awt package.

Javas AWT package provides the following: -

y A full set of user-interface (UI) widgets and other components,including windows, menus, buttons etc.

y Support for UI containers, which can contain other embeddedcontainers or UI widgets.

y An event system for managing system and user events amongparts of the AWT.


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The Major Components in the AWT: -

yContainers: - Containers are generic AWT componentsthat can contain other containers. The most common form of

container is a panel, which represent a container that can be

displayed on screen. Applets are a form of panel.

y Canvases: - A canvas is a simple drawing surface.Canvases are good for painting images or performing other

graphics operations.

y UI components:- These components can include buttons,lists, check boxes, text fields etc.

y Window construction components: - Thesecomponents include window, frames and menu bars.

The partial AWT hierarchy is shown in the diagrams:


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Components

Canvas Text components ButtonContainers

Panel Window

TextField

Applet

Frame Dialog


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BASICUSERINTERFACE (UI)COMPONENTS:-

y Label: -

The simplest form of UI component is the label, which is

effectively, a text string that can be used to label other UI

Components. In general a label can be defined as an uneditable

text String that acts as a description for other AWT components.

Syntax:

Label l1=new Label (Label Name);

add (l1);

y Buttons: -Buttons are simple UI components that trigger some action in the

interface when they are pressed.

Syntax:

Button b1=new Button (Button Name);

add (b1);


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y CheckBoxes: -Check boxes are user-interface components that have two States:

on and off. Unlike buttons, check boxes usually dont trigger direct

actions in a UI, but instead are used to indicate optional features of

some other action. Check boxes can be used in two ways:

y Nonexclusive- Given a series of check boxes, any of them can beselected.

y Exclusive- Given a series of check boxes, only one check boxfrom the series can be selected at a time.

Syntax:

Checkbox chk=new Checkbox (Shoes);

add (chk);

yRadio

Button

:

-A Radio button is hollow round. Radio Buttons only one in a series

can be selected at a time.

Syntax:

CheckboxGroup chkgrp=new CheckboxGroup ();

Checkbox chkbx=new Checkbox (item name, chkgrp, false);

add (chkbx);


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y Choice Menus or Choice Lists:-Choice menus are pop-up list of items from which one can select

an item. Choice menus can have only one item selected at a time.

Syntax:

Choice Ch=new Choice ();

Ch.add (apples);

Ch.add (orange);

add (Ch);

y Text Fields: -Text fields provide an area where one can enter and edit a singleline of text. Text fields are generally used for getting text input

from a user.

Syntax:

TextField txt=new TextField (10);

add (txt);

y Text Areas: -Text Areas are editable text fields that can handle more than one

line of text input. Text Areas are created from the TextArea class.


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Text areas have horizontal and vertical scrollbars that enable the

user to scroll through the text contained in the component.

Syntax:

TextArea taDetails=new TextArea (letter, 10, 45);

add (taDetails);

y Scrolling Lists: -Scrolling lists are similar to Choice menus or Choice lists with two

significant differences:

y A scrollbar list can be set up so that more than one item can beselected from the list at a time.

yScrolling lists do not pop-up when selected. Instead, multipleitems are displayed in a manner similar to a textArea. If the list

contains more items they can be displayed, the scrollbar is used to

move through the entire list.

Syntax:

List lt=new List (5, true);

lt. add (Raj);

lt. add (Jyoti);

lt. add (Aruna);

lt. add (Sonia);


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lt. add (Kamal );

lt. add (Preet);

add (lt);

y Scrollbars: -Scrollbars are components that enable a value to be selected by

sliding a box between two arrows. Several components have built-

in scrollbar functionality, including text areas and scrolling lists.

The Scrollbar class is used for creating scrollbars. A scrollbar can

be horizontal or vertical.

Syntax:

Scrollbar bar = new Scrollbar (Scrollbar. VERTICAL, 10, 0, 1, 100);

add (bar);


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LAYOUTS:

A layout refers to arranging and placing of the components in a

container, much like arranging the furniture in a house java has an

interface called the Layout Manager which belongs to the java.awt

package. This is used for placing objects in a container for display on

screen without specifying the row, column position. The AWT package

includes classes of the following layout manager:

y Flow Layout:-The flow layout class lays out components in amanner similar to the way words are laid out in a page, from left

to right until theres no more room, then onto the next row.

Syntax:

FlowLayout flow=new FlowLayout (FlowLayout.LEFT);

setLayout (flow);

y Grid Layout: -The grid layout manager arranges componentsinto a grid of rows and columns.

Syntax:

GridLayout grid=new GridLayout (10, 3);


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setLayout (grid);

y Border Layout:- Border layouts, which created by using theBorderLayout class, divide a container into five sections: north,

south, east, west, center.

Syntax:

BorderLayout border=new BorderLayout (10, 3);

setLayout (border);

add (North,btnNorth);

add (South,btnSouth);

add (East,btnEast);

add (West,btnWest);

add (Center,btnCenter);

y Card Layout: -A card layout is a group of containers orcomponents that are displayed one at a time. Each container in a

group is called a card.

Syntax:

CardLayout card=new cardLayout (10, 3);

setLayout (card);


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Event-Driven Programming:-

A window based application, or an applet, is quite different. The

operation of the program is driven by what is done with the GUI.

Selecting menu items of buttons using the mouse, or through the

keyboard, causes particular action within the program. The action using

the GUI for a window based program or an applet clicking a menu item

or a button, moving the mouse and so on are first identified by the

operating system. The signals that a program receives from the operating

system as a result of the actions are called events. A window based

program is called an event driven program, because the sequences of

events are created as a result of the interaction with the GUI drives and

determines what happens in the program.

Delegating the Event:-

Suppose the user clicks a button in the GUI for a program. The button is

the source of this event. The event generated as a result of the mouse

click is associated with the Button object in the program that represents

the button on the screen. An event always has a source object-in this

case the button object. When the button is clicked, it will create a new

object that represents and identifies this event in this case an object of

type Action Event. This object will contain information about the event

and its source. Any event that is passed to a java program will be

represented by a particular event object and this object will be passed as


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an argument to the method that is to handle the event. In this case it is

actionPerformed ().

Javas Event Types:

11 concrete event types, which are contained in the java.awt.event

package. All the event classes extend from two abstract superclasses:

java.util.EventObject and java.awt. There are AWTEvent. The event

inheritance hierarchy is as follow:

java.util.EventObject

java.awt.AwtEvent

Adjustment Component Item Event Text EventAction Event

Container Event Focus Event Input Event Paint Event Window Event

Mouse Event Key Event


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JDBC:

JDBC has been part of the Java Standard Edition since the release of

JDK 1.1. The JDBC classes are contained in the Java package java.sql.

Starting with version 3.0. JDBC allows multiple implementations to

exist and be used by the same application. The API provides a

mechanism for loading the correct Java packages and registering them

with the JDBC Driver Manager. The Driver Manager is used as a

connection factory for creating JDBC connections.JDBC connections

support creating and executing statements. These statements may be

update statements such as SQL CREATE, INSERT, UPDATE and

DELETE or they may be query statements using the SELECT statement.

Additionally, stored procedures may be invoked through a statement.

Statements are one of the following types:

y Statement The statement is sent to the database server eachand every time.


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y PreparedStatement The statement is cached and then theexecution path is pre determined on the database server

allowing it to be executed multiple times in an efficient manner.

Update statements such as INSERT, UPDATE and DELETE indicates

how many rows were affected in the database. These statements do not

return any other information.Query statements return a JDBC row result

set. The row result set is used to walk over the result set. Individual

columns in a row are retrieved either by name or by column number.

There may be any number of rows in the result set. The row result set

has metadata that describes the names of the columns and their types.

The ConnectivityModel Being Used: -

The java application is the UI. This in turn communicates with a driver

manager using underlying java code. The Driver Manager is a class that

Java

ApplicationThe User

Interface

32-bit

ODBCAccess

Driver

The AccessDatabase And

Its Table

Javas Driver Manager, Responsible for

setting

Up the JDBC ODBC bridge


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belongs to the java.sql package. The Driver manager in turn

communicates with the 32-bit ODBC driver. The 32-bit ODBC driver in

turn communicates with the Access database and its tables.


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Using javas Driver Manager to connect to a Database:

Choosing an appropriate driver:-

The method Class.forName(String) is used to load the JDBC driver

class. The line below causes the JDBC driver fromsome jdbc vendorto

be loaded into the application.

Class.forName( "sun.jdbc.odbc.jdbcOdbcDriver" );

The java DriverManager The ODBCSystem DSN The AccessDatabase, table

With Data in it

Creates a ConnectionObject whichCommunicates with the ODBC driver and in turn spawns a

Result Set object in hold the record set returned by the querymade to the Database table.

The Result Set ObjectThis holds the records retrieved from the Access Database, table.

Data from this result set object can be bound to controls on a java

form, i.e. the UI


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Creating a connection using the Driver Manager class:-

Now when a connection is needed, one of the

DriverManager.getConnection() methods is used to create a JDBC

connection.

Connection conn = DriverManager.getConnection(url);

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