INTRODUCTION TO JAVA PROGRAMMING

A. A LITTLE BIT OF HISTORY

Java was created in 1991 by James Gosling et al. of Sun Microsystems. Initially calledOak, in honor of the tree outside Gosling's window, its name was changed to Javabecause there was already a language called Oak.The original motivation for Java was the need for platform independent language thatcould be embedded in various consumer electronic products like toasters andrefrigerators. One of the first projects developed using Java was a personal hand-heldremote control named Star 7.At about the same time, the World Wide Web and the Internet were gaining popularity.Gosling et. al. realized that Java could be used for Internet programming.

B. WHAT IS JAVA TECHNOLOGY?

1 . A programming languageAs a programming language,

Java can create all kinds of applications that you couldcreate

using any conventional programming language.

2. A development environmentAs a development

environment, Java technology provides you with a large

suite oftools: a compiler, an interpreter, a documentation

generator, a class file packaging tool,and so on.

3. An application environmentJava technology

applications are typically general-purpose

programs that run on anymachine where

the Java runtime environment (JRE) is installed.

4. A deployment environmentThere are two main

deployment environments: First, the JRE supplied

by the Java 2Software Development Kit (SDK)

contains the complete set of class files for all the

Javatechnology packages, which includes basic

language classes, GUI component classes,and

so on. The other main deployment environment

is on your web browser. Mostcommercial

browsers supply a Java technology interpreter

and runtime environment.

C. SOME FEATURES OF JAVA

1. The Java Virtual MachineThe Java Virtual Machine

is an imaginary machine that is implemented

by emulatingsoftware on a real machine. The

JVM provides the hardware platform specifications

towhich you compile all Java technology code.

This specification enables the Java softwareto

be platform-independent because the compilation

is done for a generic machineknown as the

JVM.A bytecode is a special machine language

that can be understood by the Java

VirtualMachine (JVM). The bytecode is

independent of any particular computer

hardware, soany computer with a Java

interpreter can execute the compiled Java

program, no matterwhat type of computer

the program was compiled on.

2. Garbage CollectionMany programming

languages allows a programmer to allocate

memory during runtime.However, after

using that allocated memory, there should

be a way to deallocate thatmemory block

in order for other programs to use it again.

In C, C++ and otherlanguages the programmer

is responsible for this. This can be difficult

at times sincethere can be instances wherein

the programmers forget to deallocate memory

andtherefor result to what we call memory

leaks.In Java, the programmer is freed

from the burden of having to deallocate that

memorythemselves by having what we call the

garbage collection thread. The garbagecollection

thread is responsible for freeing any memory

that can be freed. This happensautomatically

during the lifetime of the Java program.

3. Code SecurityCode security is attained in Java

through the implementation of its Java RuntimeEnvironment

(JRE). The JRE runs code compiled for a JVM and

performs class loading(through the class loader),

code verification (through the bytecode verifier)

and finallycode execution.The Class Loader is

responsible for loading all classes needed for

the Java program. Itadds security by separating

the namespaces for the classes of the local file

system fromthose that are imported from

network sources. This limits any Trojan horse

applicationssince local classes are always

loaded first. After loading all the classes, the

memorylayout of the executable is

then determined. This adds protection against

unauthorizedaccess to restricted areas of the

code since the memory layout is determined

duringruntime.After loading the class and layouting

of memory, the bytecode verifier then tests

the format of the code fragments and checks

the code fragments for illegal code that canviolate

access rights to objects.After all of these have been

done, the code is then finally executed.

D. PHASES OF A JAVA PROGRAM

The following figure describes the process of compiling

and executing a Java program.· The first step in creating a Java

program is by writing your programs in a text editor.Examples

of text editors you can use are notepad, vi, emacs, etc. This

file is stored in adisk file with the extension .java.·After creating

and saving your Java program, compile the program by using

the JavaCompiler. The output of this process is a file

of Java bytecodes with the file extension.class.·The

class file is then interpreted by the Java interpreter

that converts the bytecodesinto the machine language

of the particular computer you are using.

Task

1. Write the program
2. Compile the program
3. Run the program

Tool to use

1. Any text editor
2. Java Compiler
3. Java Interpreter

Output

1. File with .java extension2. File with .class

extension(Java Byte Codes)3. Program Output

E. DIFFERENCE BETWEEN JAVA APPLICATIONS AND JAVA APPLETS

• Java applets are java programs that run in a web browser, it is dependent on web browsers.
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• Java applications are stand alone java programs. It can be run in a console window or a graphical user interface.
  

F. WHAT MAKES JAVA AN OBJECT ORIENTED LANGUAGE

• Java is considered as an object oriented programming language because it uses "objects" – data structures consisting of datafields and methods together with their interactions – to design applications and computer programs. Java includes features such as data abstraction, encapsulation, modularity, polymorphism, and inheritance.