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Satellite Phones - Contents Functioning of a Satellite Phones

1. Introduction

JAVA is a high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes.

Some features of java:

     1. Simple: Some of the features that make java a simple language are no direct use of pointers, strong  memory management, automatic memory allocation and deallocation.

     2. Portable: Java language is portable as programs written in java can be run on any system having interpreter for JVM. Also, java has standard size irrespective of operating system or processor.

    3. Robust: Features that make java robust include powerful exception handling, type checking mechanism, strong memory allocation and automatic garbage collection mechanism.

4.    Architecture neutral: Code written in java is compiled into byte code instructions which can be interpreted on any machine using JVM and can be easily translated into native machine code. Also, compiler generates an architecture-neutral object file format that enable a Java application to execute anywhere on the network.

5.      Object oriented: Java is an object-oriented language it uses all object-oriented concepts including classes, objects, Inheritance, polymorphism, data binding. Also java has an extensive class library in core language package.

6.      Secure: All the programs in java are run in virtual machine sand box. Java uses the public key encryption system to allow the java applications to transmit over the Internet in the secure encrypted form. The byte code Verifier checks the classes after loading, class loader confines objects to unique namespace and security manager determines the accessibility options of a class like reading and writing a file to the local disk.

7.  Threading: Threads can be used in java for multiprocessing.

2. Language Basics

 

a. Variables: There can be three types of variables in java. 

      1. Instance Variables : These are Non-Static Fields. Individual states of objects are stored in Instance variables. These 
        are declared without the static keyword. For number of objects created from a class all objects use same copy of instance
        variable.  

Example:  

import java.io.*; 


class Student{
   // this instance variable is visible for any child class.
   public String name;   
   // percentage variable is visible in Student class only.
   private double percentage;   
   // The name variable is assigned in the constructor. 
   public Student (String StudName){
      name = StudName;
   } 


   // The percentage variable is assigned a value.
   public void setPercentage(double StudPercent){
      percentage = StudPercent;
   }   
   // This method prints the Student details.
   public void PrintStudentDetails(){
      System.out.println("name  : " + name );
      System.out.println("Percentage :" + percentage);
   } 


   public static void main(String args[]){
      Student S1 = new Student("John");
      S1.setPercentage(68.89);
      S1.PrintStudentDetails();
   }
} 

 

      2.Class Variables : These are Static Fields. These are declared using static modifier. There will be only one copy of each
        class variable per class for all the objects created from that class.   

import java.io.*; 


class Student{
   // marks  variable is a private static variable
   private static int marks; 


   // Course is a constant
   public static final String Course = "IT"; 


   public static void main(String args[]){
      marks = 67;
      System.out.println(Course +"marks:"+marks);
   }
} 

      3. Local Variables : The syntax for declaring a local variable is similar to declaring a field (for example, int count = 0;).
        These are created when a method, block or constructors are entered and destroyed when it exits. There are no default
        vales for local variables and internally these are maintained at stack level. 

public class LocalVar{ 
   public void GetTotal(){
      int total = 0;
      total = total + 3;
      System.out.println("Total is : " + total)
   }   
   public static void main(String args[]){
      LocalVar L1 = new LocalVar();
      L1.GetTotal();
   }
}
Satellite Phones - Contents Functioning of a Satellite Phones
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