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

More Related Content

What's hot (20)

Similar to Java Basic PART I (20)

More from Soumen Santra (20)

Recently uploaded (20)

Java Basic PART I