 Learning JAVA.  Understanding Salient features of JAVA.  Implementing JAVA PROGRAMS on your own.  Development of JAVA PROJECTS on your own.

 About JAVA language.  Program structures  Simple program  JVM  OOP principles.  keywords  Data types  Operations  Arrays

Java History L 1.1 Computer language innovation and development occurs for two fundamental reasons: 1) to adapt to changing environments and uses 2) to implement improvements in the art of programming The development of Java was driven by both in equal measures. Many Java features are inherited from the earlier languages: B  C  C++  Java

C language designed by Dennis Ritchie in 1970s. C++ designed by Bjarne Stroustrup in In 1990, Sun Microsystems started a project called Green. Objective: to develop software for consumer electronics. Project was assigned to James Gosling, a veteran of classic network software design. Others included Patrick Naughton, ChrisWarth, Ed Frank, and Mike Sheridan. In 1994, an early web browser called WebRunner was written in Oak. WebRunner was later renamed HotJava. In 1995, Oak was renamed Java.

Java Buzzwords L 1.9  Simple  Secure  Portable  Object-oriented  Robust  Multithreaded  Architecture-neutral  Interpreted  High performance  Distributed  Dynamic

Structure of C

Structure of JAVA Document section Package section Import statements Class definitions { Variables Methods } Main Class { Main Method Definition }

/*A program to add two numbers*/ package mypack; import java.lang. *; import java. util.*; class Addition { int a,b,c; void sum(int a, int b) { c=a+b; System.out.println(“sum is +c”); } class Additionop { public static void main(String args[]) { Addition ad=new Additon(); ad.sum(3,5) }

class Welcome { public static void main(String args[]) { System.out.println(“WELCOME TO JAVA WORLD”); }

Naming conventions specify the rules to be followed by a Java programmer while writing the names of packages, classes, methods etc. Package names are written in small letters. ex: java.io, java.lang, java.awt etc Each word of class name and interface name starts with a capital ex: Sample, AddTwoNumbers Method names start with small letters then each word start with a capital ex: sum (), sumTwoNumbers (), minValue () · Variable names also follow the same above method rule ex: sum, count, totalCount · Constants should be written using all capital letters ex: PI, COUNT · Keywords are reserved words and are written in small letters. ex: int, short, float, public, void

Compiling the Program To compile the program, execute the compiler, javac, specifying the name of the source file on the command line. C:\>javac Welcome.java To actually run the program, you must use the Java interpreter, called java. To do C:\>java Welcome When the program is run, the following output is displayed: “WELCOME TO JAVA WORLD”.

Java Virtual Machine(JVM) Java compiler translate source code into machine code. java compilers produces an intermediate code known as Byte code for a machine. this machine is called Java Virtual Machine, and it exists only inside the computer memory. the virtual machine code is not machine specific, the machine code is generated by Java interpreter.

source code Byte code Process of compilation virtual machine real machine Process of converting byte code into machine code Java program Byte codeJava interpreterMachine code Java compilerVirtual machine

OOP Vs POP Object oriented programingProcedural oriented programing The unit in object-oriented programming is class.The unit in procedural programming is function. It is concerned to develop an application based on real time. POP are more concerned with the processing of procedures and functions. It providing more security to data.It providing less security to data. In OOP the Objects communicate with each other via Functions. There is no communication in POP rather its simply a passing values to the Arguments to the Functions and or procedures. OOP follows Bottom Up Approach of Program Execution. POP follows Top Down Approach of Program Execution. OOP includes Inheritance, Encapsulation and Data Abstraction, Late Binding, Polymorphism, Multithreading, and Message Passing. POP is simply a programming in a traditional way of calling functions and returning values. The list of OOL languages :- JAVA, VB.NET, C#.NET The list of PPL languages :- C, VB, Perl, Basic, FORTRAN.

PRINCIPLES Encapsulation: It is the mechanism that binds together code and the data it manipulates. info. in info. out Data &Method

Inheritance: It is the process by which objects of one class acquire the properties of objects of another class. Bird attributes Flying birds Nonflying birds RobinSwallow PenguinKiwi

Polymorphism: It means the ability to take more than one form. Shape Draw() Circle object Draw(circle) Box object Draw(box) Triangle object Draw(triangle)

CLASS L 4.3 A class is a blueprint,that defines the variables and methods common to all objects of a certain kind. An object holds values for the variables defines in the class. “Object” is an instance of a class. Each object has a class which defines its data and behavior. An object is called an instance of the Class

Structure of Class A class is declared by use of the class keyword. class classname { type instance-variable1; type instance-variable2; //... type instance-variableN; type methodname1(parameter-list) { // body of method } type methodname2(parameter-list } //... type methodnameN(parameter-list) { // body of method }

The Java Keywords abstractcontinuegotopackagesynchronized assertdefaultifprivatethis booleandoimplementsprotectedthrow breakdoubleimportpublicthrows byteelseinstanceofreturntransient caseextendsintshorttry catchfinalinterfacestaticvoid charfinallylongstrictfipvolatile classfloatnativesuperwhile constFornewswitch

Data Types L 1.14 Java defines eight simple types: 1)byte – 8-bit integer type 2)short – 16-bit integer type 3)int – 32-bit integer type 4)long – 64-bit integer type 5)float – 32-bit floating-point type 6)double – 64-bit floating-point type 7)char – symbols in a character set 8)boolean – logical values true and false

Variables L 2.2 Java uses variables to store data. To allocate memory space for a variable JVM requires: 1) to specify the data type of the variable 2) to associate an identifier with the variable 3) the variable may be assigned an initial value All done as part of variable declaration.

Variable Declaration L 2.4 datatype identifier [=value]; datatype must be A simple datatype User defined datatype (class type) We can declare several variables at the same time: type identifier [=value][, identifier [=value] …]; Examples: int a, b, c; int d = 3, e, f = 5; byte g = 22; double pi = ; char ch = 'x';

Variable Scope L 2.5 Scope determines the visibility of program elements with respect to other program elements. In Java, scope is defined separately for classes and methods: 1) variables defined by a class have a global scope 2) variables defined by a method have a local scope A scope is defined by a block: { … } A variable declared inside the scope is not visible outside: { int n; } n = 1;// this is illegal

Arrays L 2.7 An array is a group of liked-typed variables referred to by a common name, with individual variables accessed by their index. Arrays are: 1) declared 2) created 3) initialized 4) used Also, arrays can have one or several dimensions.

Array Declaration L 2.8 Array declaration involves: 1) declaring an array identifier 2) declaring the number of dimensions 3) declaring the data type of the array elements Two styles of array declaration: type array-variable[]; or type [] array-variable;

Array Creation L 2.9 After declaration, no array actually exists. In order to create an array, we use the new operator: type array-variable[]; array-variable = new type[size]; This creates a new array to hold size elements of type type, which reference will be kept in the variable array- variable.

Array Initialization L 2.11 Arrays can be initialized when they are declared: int monthDays[] = {31,28,31,30,31,30,31,31,30,31,30,31}; Note: 1) there is no need to use the new operator 2) the array is created large enough to hold all specified elements

Array Indexing L 2.10 Later we can refer to the elements of this array through their indexes: array-variable[index] The array index always starts with zero! The Java run-time system makes sure that all array indexes are in the correct range, otherwise raises a run-time error.

int[] abc, xyz; abc = new int[5]; // Instantiate an array of 5 integers xyz = abc; // xyz and abc refer to the same array xyz[3] = 100; // Changing xyz changes abc as well. System.out.println (abc[3]); // 100 is displayed

Multidimensional Arrays L 2.12 Multidimensional arrays are arrays of arrays: 1) declaration: int array[][]; 2) creation: int array = new int[2][3]; 3) initialization int array[][] = { {1, 2, 3}, {4, 5, 6} }; Two-dimensional array

Average an array of values class Average { public static void main(String args[]) { double nums[] = {10.1, 11.2, 12.3, 13.4, 14.5}; double result = 0; int i; for(i=0; i<5; i++) result = result + nums[i]; System.out.println("Average is " + result / 5); }

Two-dimensional array class TwoDArray { public static void main(String args[]) { int twoD[][]= new int[4][5]; int i, j, k = 0; for(i=0; i<4; i++) for(j=0; j<5; j++) { twoD[i][j] = k; k++; } for(i=0; i<4; i++) { for(j=0; j<5; j++) System.out.print(twoD[i][j] + " "); System.out.println(); }

Output

Operators Types L 2.13 Java operators are used to build value expressions. Java provides a rich set of operators: 1) assignment 2) arithmetic 3) relational 4) logical 5) bitwise

Arithmetic assignments +=v += expr;v = v + expr ; -=v -=expr;v = v - expr ; *=v *= expr;v = v * expr ; /=v /= expr;v = v / expr ; %=v %= expr;v = v % expr ; L 2.14

Basic Arithmetic Operators +op1 + op2ADD -op1 - op2SUBSTRACT *op1 * op2MULTIPLY /op1 / op2DIVISION %op1 % op2REMAINDER L 2.15

Relational operator ==Equals toApply to any type !=Not equals toApply to any type >Greater thanApply to numerical type <Less thanApply to numerical type >=Greater than or equalApply to numerical type <=Less than or equalApply to numerical type L 2.16

Logical operators &op1 & op2Logical AND |op1 | op2Logical OR &&op1 && op2Short-circuit AND ||op1 || op2Short-circuit OR !! opLogical NOT ^op1 ^ op2Logical XOR L 2.17

Bitwise operators program class Bits { public static void main(String args[]) { byte x,y; x=10; y=11; System.out.println("~x="+(~x));-> -11 System.out.println("x&y="+(x&y));-> 10 System.out.println("x/y="+(x/y));-> 11 System.out.println("x^y="+(x^y));-> 1 System.out.println("x 40 System.out.println("x>>2="+(x>>2));-> 22 System.out.println("x>>>2="+(x>>2));-> 22 }

presented by U. LOVARAJU Assoc. Professor IT-Department