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While writing code, comments are important to consider because it is helpful for others to read your code and for yourself as well.

There are two different styles of Java comments:  C style and C++ style.  A C style comment begins with /* and ends with */.   C style comments are used to document information that applies to the entire program or the block of code.   For example: 

/**************************************************************************** 
 Due date: 1/1/2015
Author:  Albert Einstein
Description: This program is to prompt user to enter student scores, calculate the average, and display the result to the console. 
*****************************************************************************/ 


  A C++ style comment begins with double slashes // and is followed one line of explanation.  You must begin each line of a multi-line comment block with //.  It is used to describe what a specific statement or group of the statements do.   For example: 
 float sum, average;  //declare float type of variables 
 //compute the average and display the result 
 average = sum / 5; 
 System.out.println(“Average = “ + average);  //Concatenation using a "+" sign


Identifiers : 

            Identifiers are the names created by a programmer within a program.  Variable names, class names, and method names are examples of identifiers.  Identifiers cannot be any keywords reserved by the Java language.  You must use the following rules in creating an identifier: 

• An identifier starts with one of any letter, underscore _, or dollar sign $. 


• It is followed by the combination of any letters, numbers (0-9), underscores, and dollar signs. 


• It cannot be the same as any Java keyword. 


The following are 53 Java keywords: (cannot be used by the programmer!)

  abstract assert  boolean break  byte  case  catch char  class  const  continue default  do  double else  enum  extends  false  final  finally  float for   goto  if  implements import  instanceof  int interface  long  native  new  null   package private protected  public  return  short   static  strictfp  super switch  synchronized this  throw  throws  transient true  try  void    volatile  while 


Primitive Data types:
               Variable is a memory location where data can be stored. Java Provides 8 Different data types to store data.
  
             Type                        Name                  Memory Requirement(in bytes)                  Value Range
    
           byte                    integer in byte                               1                                                           -128 , -127


          short                   short integer                                   2                                                     -32768,  -32767


            int                           integer                                          4                        -2,147,483,648 to -2,147,483,647


         long                   integer in long                                  8   -9,223,372,036,854,775,808 9,223,372,036,854,775,807 


           float                    single float                                        4                              -3.4E38 – 3.4E38 (up to 7 significant digits)


     double                        double float                                     8                         -1.7E308 – 1.7E308 (up to 16 significant digits)


        char                    single character                               2                                                 Unicode character 


  boolean                  Boolean                                               1                                                      true or false




Integer type variables, such as byte, short, int, and long, can only store whole numbers, while float and double variables store data as floating-point numbers.  If a single-precision floating-point variable exceeds 7 significant digits, e.g., 123456.75, the eighth digit will be rounded up in the stored value.  Java will display bigger or smaller floating-point numbers with scientific notation E.   For example, 28600000.0 will be 2.86E7, and .000123 will be 1.23E-4. 

NOTE  :  String is not a primary data type.  It is provided by the Java language as an API (Application Programming Interface) class, or library class.  We can tell String is a class as its name begins with an uppercase letter.  Since String is a commonly used data type, Java provides a convenient way, direct referencing  (referencing, in short) to define a String object.  For example: 

 String obj = “I am a String”;     //obj referencing to a String object 
   
  
      
Variable Initialization:  
Examples : 
    int a;
    a = 1;  //storing or assigning 1 to a

or    int a  = 1;   //Single Statement

double value ;
value = 2.49;
or
double value  =2.49   // Single Statement 
   

boolean  isValid  =   true  ;


char letterB = 'B';   //Storing Letter B in the variable "letterB"

Operators:
 
     2 + 3  // Arithmetic operation
In the above operation , "+" is a operator and 2, 3 are operands.


+      ---MEANING-----> adding of two operands
-       ---MEANING-----> Subtraction of the right operand from the left operand
*      ---MEANING------>Multiplication of two operands
/      ---MEANING------>Division of left operand from the right operand
%   ---MEANING------->Reminder after division.
++  ---MEANING------->Increment
--  ---MEANING------> Decrement
+  ---MEANING ------> Positive Sign
-  ----MEANING------> Negative Sign

There are 4 different ways to increase a variable by 1: 
 x = x + 1;             //regular 
  x += 1;                //short-cut 
  ++x;                    // prefix incrementing 
  x++;                    // postfix incrementing



Concatenation:
            Joining Strings are very easy in Java.

               String  firstName = "John", 
           String lastName = "Smith"; 
           String fullName = firstName + " "+ lastName;    
 //Joining Strings 

Output  : John Smith

Using Special Character in Java  :
      
We must place a backslash “\” before a special character when it is used in a string.  This notation is called an escape sequence. The first 3 escape sequences in the table control the cursor’s locations.  The fourth one is used with a double quote. 
   
 Escape Sequence                      Example                                                                                USE       

            \n                               String newline = "\nn";                                          Move cursor to beginning of 

                                                                                                                                              next line and display n
                                                                                                                                              when string is displayed 


             \t                                String val = "u\tv";                                                   Separate u and v with a tab 
                                                                                                                                             character in the output


             \r                              String end = "none\r";                                              Position cursor at character "n"
                                                                                                                                             when string is displayed.


             \"                             String lang = "\"C++\" OOP";                            Will display " C++"  OOP
    
            \\                              String backSlash =" D:\\\\dir"  ;                       Will display D:\\dir                                 




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  • Home
  • React.js
  • Java Tutorial
    • Introduction
    • Setting up the environment : Netbeans
    • Basics
    • FirstApp
    • Classes and Objects
    • Commonly Used Packages
    • Celsius to Fahrenheit Converter App
    • Celsius to Fahrenheit Using JOptionPane
    • Exception Handling
    • TestGradeApp
  • Objective-C
  • Python-Django
  • Contact