Java Basic PART I

Java Basic PART I Soumen Santra MCA, M.Tech, SCJP, MCP

Java Write Once, Run Anywhere IN ANY PLATFORMONE SOURCE CODE

Java : Components Editor: Write the source code. Linker: Link the Source code with the library files. Java Compiler – Keyword javac use as convert Java source code to bytecode. Bytecode - An intermediate form, known as native code, closer to machine code. JVM-Java Virtual Machine , a concept of target platform which interprets the bytecode. Interpreter-The interpreter demonstrates the platform independent .class file to equivalent machine dependent code to run. Keyword java. Javadoc-API Documentation generator. JRE- Java Runtime Environment.

Java : Features JVM uses bytecodes as .class file. Light-weight Small binary class files for fast execution. Just-in-time (JIT) Compilers for compiling only changes code. Multithreading for high process and memory management. Native Methods Interfaces as JNDI. Native Methods Libraries.

Java : Features (Cont..) Class Loader. Dynamic. Good communication constructs. Secure. Portable and Compatible. Understandable and easy-to-write. Fully Object Oriented. Support Console based, Windows based and Web based application. Case-sensitive. JRE. Jdk (Java Development toolkit).

General Language Features C/C++ like syntax, ends with ; No pointers concept. Objects taken all controls. Objects communicates with objects through messages. Messages result in invocation of class methods.

Java : Security Language designed as safe. Strict compiler javac & JIT. Dynamic Runtime Loading (Verifier). Runtime Security Manager. Jar- Create & manage all the java archive files. Method area. Heap. JVM language stacks. Pc registers. Native method stacks. Java kernel.

Security Manager Prevents unauthorized disk read/writes. Restricts network access without creating dynamic link library files. Restricts Other access (native methods). Implementation is browser or processor dependent.

Object Oriented Languages Comparison with java C++ Objective C Ada Java Encapsulation Yes Yes Yes Yes Inheritance Yes Yes No Yes Multiple Inheritance Yes Yes No No Polymorphism Yes Yes Yes Yes Binding (Early/Late) Both Both Early Both Concurrency Poor Poor Difficult Yes Garbage Collection No Yes No Yes Genericity Yes No Yes No Class Libraries Yes Yes Limited Yes FEATURES

Features Removed From C++ Operator overloading. Pointers of Array/pointers. Multiple-inheritance of implementation through class inherit concept. Enum, typedef, #define. Copy constructors, destructors. Templates. And many more....

Added or Improved over C++ Interfaces over class. Garbage collection. Exceptions (More featureful than C++). Strings and many implementation. Instanceof. Package. Multi-threads.

Java better than C++ No Typedefs, Defines, or Preprocessor. No Global Variables. No goto statement. No Pointers. No Unsafe Structures. No Multiple Inheritance. No Operator Overloading. No Automatic Coercions. No Fragile Data Types. No copy constructor.

Basic Data Types Data Types boolean either true of false char 16 bit Unicode 1.1 byte 8-bit integer (signed) short 16-bit integer (signed) int 32-bit integer (signed) long 64-bit integer (signed) float 32-bit floating point double 64-bit floating point String (class for manipulating strings) String, StringBuilder, StringBuffer, StringTokenizer  Java uses Unicode to represent characters internally.

Java Integrates Power of Compiled Languages and Flexibility of Interpreted Languages  Applet.  Swing & Layout Manager.  Hibernate.  Struts.  Spring  Servlet  Java Server Pages (JSP)  Java Bean.  Enterprise Java Bean (EJB).  J2ME.  Junit.  & Many More.

Power of Java and the Web Deliver .exe, not just .class. Remove porting. Remove end-user installation. Remove software distribution costs. Access by millions of customers through web.

Applications : Types Different possibilities to write/run a Java codes are: Application- A stand-alone program that can be invoked from command line through console which has a “main” method. Applet- A program embedded in a web page , to be run when the page is browsed . A program that contains no “main” method. Application -Java interpreter Applets- Java enabled web browser (Linked to HTML via <APPLET> tag. in html file or run through Appletviewer).

Java Bytecodes move locally or through network Java Source code (.java) Java Compiler Java Bytecode (.class ) Java Interpreter Just in Time Compiler Runtime System Class Loader Bytecode Verifier Java Class Libraries Operating System Hardware Java Virtual machine Runtime Environment Compile-time Environment Life Cycle of Java Code

Java Development Kit javac – Name of the Java Compiler. java - Name of the Java Interpreter. jdb- Name of the Java Debugger. appletviewer - Name of the Tool to run the applets code and give Applet window. javap – Use to print the Java bytecodes. javaprof - Name of the Java profiler. javadoc - Name of the documentation generator. javah - Name of the creates C header files. Javak= Name of the Kernel of the java.

Bytecode Verifier It Called when the class is first loaded in runtime environment by JRE. It Verifies the bytecodes meet certain set of properties. Verified code runs faster through JRE. After verification, interpreter defines memory layout. Release all memories through Garbage collector.

Java Example : Hello World // HelloWorld.java: Hello World program class HelloWorld { public static void main(String args[]) { System.out.println(“Hello World of Java”); } }

Program Processing for Output Compilation # javac HelloWorld.java outputs in HelloWorld.class Execution # java HelloWorld Hello World of Java #

Simple Java Applet Example // HelloApplet.java: A sample applet import java.applet.*; public class HelloApplet extends Applet { public void paint(Graphics g) { g.drawString(“Hello Applet !”,250,250); } } Prints Hello Applet ! In Applet window At (250,250) (x,y) coordinate

Execution of an Applet by HTML <HTML> <TITLE> Hello Applet </TITLE> <APPLET code=“HelloApplet.class” width=500 height=500 align=“right ”> </APPLET> </HTML>

Mechanism of Applets Hello Applet HelloApplet Java <app= “HelloApplet ”> 4 APPLET Development “HelloApplet.java” At terminal The Web HelloApplet .class AT WEB SERVER 2 31 5 Create Applet tag in HTML document Accessing from Client The browser creates a new window and a new thread and then runs the code

Sequence Diagram : Classic Web Perspective

Sequence Diagram : Java Web Interaction

Significance of downloading Applets Interaction with World wide web w3 consortium. Dynamic animated web page instead of static web pages. Applets react to users interactive application. Could not connect network activity. Do not create dynamic link library files in cookies.

Used Java Main Packages java.lang (by default added) java.util java.io java.awt java.awt.image java.applet java.net java.sql

Java Basic PART I

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Java Basic PART I