1. 1. Introduction to JAVA 1 Infobizzs.com
2. 2. Introduction History Java is related to C++, which is a direct descendent of C. Much of the character of Java is inherited from these two languages. From C, Java derives its syntax. Many of Javas object-oriented features were determined by C++. Java was developed by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems, Inc.in 1991. It took 18 months to develop the first working version. This language was initially called Oak but was renamed Java in 1995. 2 Infobizzs.com
3. 3. Comparison between OOP and pure OOP Unlike C++, java is pure object oriented programming language. Pure OOP organizes a program around its data (i.e. objects) and set of well defined interfaces (i.e. methods) to that data. Pure OOP means all of the data types in the language are objects and all of the operations on those objects are methods. You cant code anything in java without declaring classes and objects. Everything in java is an object. All the program codes and data resides within classes and objects.3 Infobizzs.com
4. 4. Advantages of java Simple: If you already understand the basic concepts of object-oriented programming, moving to Java will require very little effort because Java inherits the C/C++ syntax and many of the object-oriented features of C++. Java was designed to be easy to use and is therefore easy to write, compile, debug, and learn than other programming languages. 4 Infobizzs.com
5. 5. Continue Secure: When you use a Java-compatible Web browser, you can safely download Java applets without fear of viral infection. Java achieves this protection by providing a firewall between a networked application and your computer. Java system not only verify all memory access but also ensure that no viruses are communicated with an applet. The absence of pointers in java ensures that programs cannot gain access to memory5 Infobizzs.com
6. 6. Continue Portable and Platform Independent: One of the most significant advantages of Java is its ability to move easily from one computer system to another. Today many types of computers and operating systems are in used throughout the world and many are connected to the Internet. We can download a java applet from a remote computer onto our local system via internet and execute it locally. You can run java program on any type of operating system because of its portability.6 Infobizzs.com
7. 7. Continue Object- Oriented: One of the most key features of java is Object Oriented. Java is object-oriented because programming in Java is centered on creating objects, manipulating objects, and making objects work together. This allows you to create modular programs and reusable code. 7 Infobizzs.com
8. 8. Continue Robust: Robust means reliable. It provides many safeguards to ensure reliable code. It has strict compile time and runtime checking for data types. In C/C++, the programmer must manually allocate and free all dynamic memory. This sometimes leads to problems, because programmers will either forget to free memory that has been previously allocated or, worse, try to free some memory that another part of their code is still8 Infobizzs.com
9. 9. Continue Java virtually eliminates these problems by managing memory allocation and deallocation. Deallocation is completely automatic, because Java provides garbage collection for unused objects. Java also incorporates the concept of exception handling which captures serious errors and eliminates any risk of crashing the system. 9 Infobizzs.com
10. 10. Continue Multithreaded: Java supports multithreaded programming, which allows you to write programs that do many things simultaneously. Architecture-Neutral: Nowadays Operating system upgrades, processor upgrades, and changes in core system resources can all combine that make a program failure and doesnt work properly. Once you written a java program, you can run this program anywhere, anytime forever. 10 Infobizzs.com
11. 11. Continue Interpreted and High Performance: The output of a Java compiler is not executable code. Rather, it is bytecode. The Java bytecode was carefully designed so that it would be easy to translate directly into native machine code for very high performance by using a just-in-time compiler. 11 Infobizzs.com
12. 12. Continue Compiled and Interpreted: Usually, a computer language is either compiled or interpreted. Java combines both these approaches. Thus making java a two stage system. First, java compiler translates source code into bytecode. Bytecodes are not machine instructions and therefore, in the second stage, java interpreter generates machine code that can be directly executed by the machine that is running the java program. We can thus say that java is both a compiled and an interpreted language. 12 Infobizzs.com
13. 13. Continue Distributed: Distributed computing involves several computers on a network working together. Java is designed to make distributed computing easy with the networking capability that is inherently integrated into it. Writing network programs in Java is like sending and receiving data to and from a file. For example, three programs running on three different systems, communicating with each other to perform a joint task. 13 Infobizzs.com
14. 14. Continue Dynamic: Java programs carry with them substantial amounts of run-time type information that is used to verify and resolve accesses to objects at run time. This makes it possible to dynamically link code in a safe manner. 14 Infobizzs.com
15. 15. Features of java Encapsulation Encapsulation is the mechanism that binds together code and the data it manipulates, and keeps both safe from outside interference and misuse. Or The wrapping up of data and methods into single unit is known as encapsulation. 15 Infobizzs.com
16. 16. Continue Inheritance Inheritance is the process by which one object acquires the properties of another object. This is important because it supports the concept of hierarchical classification. For example, the bird sparrow is a part of the class flying bird, which is again a part of the class bird. 16 Infobizzs.com
17. 17. Continue 17 Infobizzs.com
18. 18. Continue Polymorphism Polymorphism is a feature that allows one interface to be used for a general class of actions. The concept of polymorphism is often expressed by the phrase one interface, multiple methods. This means that it is possible to design a generic interface to a group of related activities. 18 Infobizzs.com
19. 19. What is byte code? The output of a Java compiler is not executable code. it is bytecode. Bytecode is a highly optimized set of instructions to be executed by the Java run-time system, which is called the Java Virtual Machine (JVM). JVM is an interpreter for Bytecode. Bytecodes are a set of instructions that is not specific to any one processor. When we compile a program written in C or in most other languages, the compiler translates our program into machine codes. Those instructions are specific to the processor your computer is running. 19 Infobizzs.com
20. 20. Continue So, for example, if you compile your code on a Pentium system, the resulting program will run only on other Pentium systems. If you want to use the same program on another system, you have to go back to your original source, get a compiler for that system, and recompile your code. Things are different when you write code in Java. The Java development environment has two parts: a Java compiler and a Java interpreter. The Java compiler takes your Java program and instead of generating machine codes from your source files, it generates bytecodes. 20 Infobizzs.com
21. 21. Continue Traditional compiled programs 21 Infobizzs.com
22. 22. Continue To run a java program, you run a program called a bytecode interpreter, which in turn executes your Java program. Having your Java programs in bytecode form means that instead of being specific to any one system, your programs can be run on any platform and any operating or window system as long as the Java interpreter is available. Only the JVM needs to be implemented for each platform. once the run-time package exists for a given system, any Java program can run on it. 22 Infobizzs.com
23. 23. Continue Java programs 23 Infobizzs.com
24. 24. Applications of java To develop web browser To enhance capabilities of web browser. To develop web server To enhance capabilities of web server To develop protocols Java encryption/decryption algorithm implementation enables security on the internet. 24 Infobizzs.com
25. 25. Basic structure of java program suggested optional optional optional optional Essenti al 25 Infobizzs.com
26. 26. Continue Documentation Section : The documentation section comprises a set of comment lines. In addition to two styles of comments, java also uses a third style of comment /**..*/ known as documentation comment. Package Statement : The first statement allowed in a java file is a package statement. This statement declares a package name and informs the computer that the classes defined here belong to this package. The package statement is optional. Ex: package student26 Infobizzs.com
27. 27. Continue Import Statements: The next thing after package statement is import statements. This is similar to the #include statement in C. Ex: import student test; This statement instructs the interpreter to load the test class contained in the package student. Using import statements, we can have access to classes that are part of other named packages. 27 Infobizzs.com
28. 28. Continue Interface Statements: An interface is like a class but includes a group of method declarations. This is also an optional section and is used only when we wish to implement the multiple inheritance feature in the program. Class Definitions: A java program may contain multiple class definitions. Classes are the primary and essential elements of a java program. 28 Infobizzs.com
29. 29. First simple program 29 Example.java class Example { public static void main (String args []) { System.out.println ("Hello World."); } } Infobizzs.com
30. 30. Compiling the program 30 To compile the Example program, execute the compiler, javac, specifying the name of the source file on the command line, as shown here: C:>javac Example.java The javac compiler creates a file called Example.class that contains the bytecode version of the program. The Java bytecode is the intermediate representation of your program that contains instructions the Java interpreter will execute. Thus, the output of javac is not code that can be directly executed. Infobizzs.com
31. 31. Run the program 31 To actually run the program, you must use the Java interpreter, called java. To do so, pass the class name Example as a command-line argument, as shown here: C:>java Example When the program is run, the following output is displayed: Hello World. Infobizzs.com
32. 32. Continue 32 When Java source code is compiled, each individual class is put into its own output file named after the class and using the .class extension. When you execute the Java interpreter as just shown, you are actually specifying the name of the class that you want the interpreter to execute. It will automatically search for a file by that name that has the .class extension. If it finds the file, it will execute the code contained in the specified class. Infobizzs.com
33. 33. Description 33 class Example This line uses the keyword class to declare that a new class is being defined. Example is an identifier that is the name of the class. public static void main (String args []) This line begins the main ( ) method. This is the line at which the program will begin executing. All Java applications begin execution by calling main ( ). Infobizzs.com
34. 34. Continue 34 The public keyword is an access specifier, which allows the programmer to control the visibility of class members. In this case, main ( ) must be declared as public, since it must be called by code outside of its class when the program is started. The keyword static allows main ( ) to be called without having to instantiate a particular instance of the class. This is necessary since main ( ) is called by the Java interpreter before any objects are made. The keyword void simply tells the compiler that main ( ) does not return a value. Infobizzs.com
35. 35. Continue 35 In main ( ), there is only one parameter, String args [ ], which declares a parameter named args, which is an array of instances of the class String. In this case, args receives any command- line arguments present when the program is executed. System.out.println ("Hello World."); This line outputs the string hello World. followed by a new line on the screen. Output is actually accomplished by the built-in println ( ) method.In this case,println( ) displays the string which is passed to it. Infobizzs.com
36. 36. Continue 36 System is a predefined class that provides access to the system, and out is the output stream that is connected to the console. Infobizzs.com
37. 37. Java input output operators 37 I/O streams A stream in java is a path along which data flows. It has a source and destination. Input stream reads the data from source and pass the data to program. Output stream writes the data from program to destination. Infobizzs.com
38. 38. Java stream classes 38 Java streams Byte Stream Character Stream I/P Stream O/P Stream Reader Writer File I/P Stream Data I/P Stream Object I/P Stream Buffered I/P Stream File O/P Stream Data O/P Stream Object O/P Stream Buffered O/P Stream Infobizzs.com
39. 39. Continue 39 The most basic java I/O is writing to and reading from console. Java contains the built-in system, input stream and print stream classes to perform these operations. To read from the keyboard, the statement System.in.read(); It will read a sequence of characters until the end of stream, i.e.the enter key has been detected or an exception has been thrown. To write data to the screen, Sytem.out.println(hi); Infobizzs.com
40. 40. Reading a data from keyboard 40 import java.io.*; public class Echo { public static void main(String args[]) throws IOException { InputStreamReader reader; BufferedReader bufReader; reader=new InputStreamReader(System.in); bufReader=new BufferedReader(reader); String s; while(null!=(s=bufReader.readLine())) System.out.println(s); } } Output: Hello world Hello world Infobizzs.com