1. 04/07/041 Intro to JAVA By: Riyaz Malbari

2. 04/07/042 History of JAVA  Came into existence at Sun Microsystems, Inc. in 1991.  Was initially called “ Oak ” but was renamed JAVA.  Originally it was not developed for the Internet but as a software to be embedded in various consumer electronic devices.  Derives much of its character from C/C++.

3. 04/07/043 Types of Programs Applications  a program that runs on the computer, under its operating system.  it is like a normal program created using C/C++. Applets  a tiny JAVA program that can be transmitted over the Internet.  it is an intelligent program.

4. 04/07/044 Bytecode  output of a JAVA compiler is Bytecode.  executed by the JAVA run-time system, which is called the JAVA Virtual Machine (JVM).  creates truly portable programs.  assures security while downloading programs over the Internet.

5. 04/07/045 JAVA Virtual Machine

6. 04/07/046 Object-Oriented Programming The core of JAVA  Encapsulation  Inheritance  Polymorphism

7. 04/07/047 A simple program  /* A program to display the message Hello World. Call this file “ hello.java ”. */ class hello { // The program begins with a call to main(). public static void main (String args [ ]) { System.out.println ( “ Hello World. ” ) ; }  save as text file hello.java  at command line type>javac hello.java  execute program by typing>java hello

8. 04/07/048 Data Types TypeSizeRange byte8 bits-128 to 127 short16 bits-32768 to 32767 int32 bits-2147483648 to 2147483647 long64 bits-9223372036854775808 to 9223372036854775807 float32 bits1.7e-308 to 1.7e308 double64 bits3.4e-038 to 3.4e038 char16 bits0 to 65536 boolean---------true or false

9. 04/07/049 Variables  basic unit of storage  a combination of an identifier, a type and an optional initializer  Syntax: type identifier [=value][, identifier[=value], … ];  eg. int a,b,c; int d=4, e, f=7; byte w=12; double pi=3.14159; char x= ‘ x ’ ;  Dynamic initialization: class DyIn { public static void main (String args[ ]) { double a=3.0, b=4.0 ; double c=Math.sqrt (a*a+b*b) ; // c is dynamically initialized System.out.println ( “ Hypotenuse is “ + c); }

10. 04/07/0410 Variable scope  scope is defined by a block { }  variables that are defined within the scope are not visible to the code that is defined outside the scope.  scopes can be nested  objects declared in the outer scope will be visible to code within the inner scope  eg. class Scope { public static void main (String args[ ]) { int x ; // known to all code within main x=10; if (x= =10) { int y=20; // known only to this block System.out.println ( “ x and y: ” + x + “ “ + y +) ; x=y*2; } y = 100; // y is unknown here and so there is a compile-time error }  variables declared in the inner and outer scope cannot have the same name  eg. class scopeerr { public static void main (String args[ ]) { int a=10; { int a=20; // Compile-time error as variable ‘ a ’ is already defined }

11. 04/07/0411 Arrays  collection of variables of the same data type addressed by a common name  an array element is accessed by its index  can have one or more dimensions  one-dimensional array: declaration: type var_name[ ]; eg. int month[]; allocation: var_name=new type[size]; eg. month = new int[12]; both can be done together: int month[ ] = new int[12]; assignment: month[0] = 31; month[1] = 28;  values can also be assigned during declaration: int month[ ] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};  Multi-dimensional arrays: int twoD[ ][ ] = new int[2][3]; [0][0][0][1][0][2] [1][0][1][1][1][2]

12. 04/07/0412 Class  fundamental concept in JAVA  defines a data type which can be used to create objects of that type  class is a template for an object and object is an instance of a class  declared by the class keyword  Syntax: class classname type var; type methodname (parameter list) { // body of method } Class Methods Instance variables Class Members

13. 04/07/0413 Example …  class Box { double width; double height; // This class declares an object of type Box. double depth; } class BoxDemo { public static void main (String args[ ]) { Box mybox = new Box(); // An object called mybox is created double vol; // Assign values to mybox ’ s instance variables. mybox.width = 10; mybox.height = 20; mybox.depth = 15; vol = mybox.width * mybox.height * mybox.depth; System.out.println ( “ The volume is “ + vol) ; }  Save the file as BoxDemo.java  Compilation creates two.class files, one for Box and the other for BoxDemo  Execute the BoxDemo.class file

14. 04/07/0414  changing the instance variables of one object have no effect on that of another  class Box { double width; double height; double depth; } class BoxDemo { public static void main (String args[ ]) { Box mybox1 = new Box(); Box mybox2 = new Box(); double vol; mybox1.width = 10; mybox1.height = 20; mybox 1.depth = 15; mybox2.width = 3; mybox2.height = 6; mybox2.depth = 9; vol = mybox1.width * mybox1.height * mybox1.depth; System.out.println ( “ The volume is “ + vol) ; vol = mybox2.width * mybox2.height * mybox2.depth; System.out.println ( “ The volume is “ + vol) ; }

15. 04/07/0415  adding a method to the box class …  class Box { double width; double height; double depth; void volume() { System.out.println ( “ Volume is ” + (width * height * depth)) ; } class BoxDemo { public static void main (String args[ ]) { Box mybox = new Box(); double vol; mybox.width = 10; mybox.height = 20; mybox.depth = 15; mybox.volume(); }

16. 04/07/0416  Returning a value …  class Box { double width; double height; double depth; double volume() { return width * height * depth ; } class BoxDemo { public static void main (String args[ ]) { Box mybox = new Box(); double vol; mybox.width = 10; mybox.height = 20; mybox.depth = 15; vol = mybox.volume(); System.out.println ( “ Volume is “ + vol) ; }

17. 04/07/0417 Constructors  initializes the object immediately upon creation  has the same name as that of the class  class Box { double width; double height; double depth; Box() { // A constructor for the Box class width = 10; height = 20; depth = 15; } double volume() { return width * height * depth ; } class BoxDemo { public static void main (String args[ ]) { Box mybox = new Box(); double vol; vol = mybox.volume(); System.out.println ( “ Volume is “ + vol) ; }

18. 04/07/0418 Method Overloading  implementation of polymorphism  two or more methods within the same class have the same name but different parameter declarations  overloaded methods must differ in the type and/or number of their parameters  class OverloadDemo { void test() { System.out.println ( “ No parameters ” ) ; } void test(int a) { // Overload test for one integer parameter System.out.println ( “ a: ” + a) ; } void test(int a, int b) { // Overload test for two integer parameters System.out.println ( “ a and b: ” + a + “ “ + b) ; } class Overload { public static void main (String args[ ]) { OverloadDemo ob = new OverloadDemo() ; ob.test(); ob.test(10); ob.test(10, 20); }

19. 04/07/0419 Inheritance  defines a general class that defines traits common to a set of related items  other specific classes add things that are unique to it  a class that is inherited is called a superclass while the one that does the inheriting is called the subclass  the extends19 keyword is used to inherit a class  multilevel hierarchies can be created

20. 04/07/0420 class A { // Creating a superclass A int i, j; void showij() { System.out.println (“i and j: “ + i +” “ + j) ; } class B extends A { // Creating a subclass B by extending class A int k; void showk() { System.out.println (“k: “ + k) ; } void sum() { System.out.println (“i + j + k: “ + (i +j + k)) ; } class Inheritance { public static void main (String args[]) { A superOb = new A(); B subob = new B(); superOb.i = 10; superOb.j = 20; superOb.showij(); subOb.i = 3; subOb.j = 6; subOb.k = 9; subOb.showij(); subOb.showk(); subOb.sum(); }

21. 04/07/0421 Packages  partitions the class name space  classes defined in a package are not accessible by code outside that package  syntax: package package_name;  the import statement is used to bring certain packages or the entire package into visibility  package Demo; class Balance { String name; double bal; Balance(String n, double b) { name = n; bal = b; } void show() { System.out.println(name + “ : $ ” + bal) ; } class AccBal { public static void main(String args[ ]) { Balance current[] = new Balance[3] ; current[0] = new Balance( “ Bush ”, 0.99); current[1] = new Balance( “ Donald ”, 9.99); current[2] = new Balance( “ Rice ”, 19.99); for (int i=0; i<3; i++) current[i].show() ; }

22. 04/07/0422 Access Specifiers  public No restrictions. Accessible from anywhere.  private Only accessible from within the class.  package Accessible from package members.  protected Also accessible from subclasses and package members.

23. 04/07/0423 JAVA for Security Basic concepts:  Authentication  Authorization  Confidentiality  Integrity JAVA tools:  JAAS (JAVA Authentication And Authorization Service)  JSSE (JAVA Secure Socket Extensions)  GSS-API (JAVA Generic Security Service Application Programming Interface)

24. 04/07/0424 JAVA Security Mechanisms AuthenticationAuthorizationConfidentialityIntegrity JAASXX JSSEXXX GSS-APIXXX

25. 04/07/0425 Thank you!