Showing posts with label Java tutorials. Show all posts
Showing posts with label Java tutorials. Show all posts

Monday, 21 January 2013

Code Comments in Java Program

Commenting Methods used in Java Program

Code comments in JAVA Source Code

Code comments are placed in source files to describe what is happening in the code to someone who might be reading the file, to comment-out lines of code to isolate the source of a problem for debugging purposes, or to generate API documentation. To these ends, the Java language supports three kinds of comments: double slashes, C-style, and doc comments.

Double Slashes

Double slashes (//) are used in the C++ programming language, and tell the compiler to treat everything from the slashes to the end of the line as text.

//A Very Simple Example

class ExampleProgram {
          public static void main(String[] args){
          System.out.println("I'm a Simple Program");

C-Style Comments

Instead of double slashes, you can use C-style comments (/* */) to enclose one or more lines of code to be treated as text.

/* These are C-style comments */
class ExampleProgram {
         public static void main(String[] args){
         System.out.println("I'm a Simple Program");

Doc Comments

To generate documentation for your program, use the doc comments (/** */) to enclose lines of text for the javadoc tool to find. The javadoc tool locates the doc comments embedded in source files and uses those comments to generate API documentation.

/** This class displays a text string at 
* the console.
class ExampleProgram {
          public static void main(String[] args){
          System.out.println("I'm a Simple Program");

Saturday, 19 January 2013

JAVA Program to Add Two Numbers


A program to accept two numbers from keyboard and calculate the sum.

//A small java program to add two numbers

import java.util.Scanner;

class AddTwoNumbers
   public static void main(String args[])
      int a, b, c;
      System.out.println("Enter two integers to calculate the sum ");
      //A simple text scanner which can parse primitive types and strings using regular                                      expressions.
      Scanner in = new Scanner(;
      //Capturing the scanned token as Int and storing it to the variables a and b.
      a = in.nextInt();
      b = in.nextInt();
      c = a + b;
      System.out.println("Sum of entered integers = "+c);


Enter two integers to calculate the sum
Sum of entered integers = 25

Thursday, 17 January 2013

Addition of Two Numbers Java Programming Code

Java program to add two numbers

Simple Program to Add two numbers in Java

//A Simple Program to Add Two Numbers in Java Program.

class AddTwoNumbers        //Class Declaration
   public static void main(String args[]) //Main Function
      int x, y, z;      // Variable Declaration
      x = 10;           //Assigning 10 to the variable x.
      y = 20;           //Assigning 20 to the variable y.
      z = x + y;        //Expression to Add two variables x, y and save the result to z
      System.out.println("Sum of x and y = "+z); //This line output the value of z on the Screen


Sum of x and y =30

Wednesday, 16 January 2013

Java Separators

Separators in Java

Separators used in Java Programming Lanuage

Separators help define the structure of a program. The separators used in HelloWorld are parentheses, ( ), braces, { }, the period, ., and the semicolon, ;. The table lists the six Java separators (nine if you count opening and closing separators as two). Following are the some characters which are generally used as the separators in Java.

It is used to separate the package name from sub-package name & class name. It is also used to separate variable or method from its object or instance.
It is used to separate the consecutive parameters in the method definition. It is also used to separate the consecutive variables of same type while declaration.
It is used to terminate the statement in Java.
This holds the list of parameters in method definition. Also used in control statements & type casting.
This is used to define the block/scope of code, class, methods.
It is used in array declaration.
Separators in Java

Sunday, 13 January 2013

Java Literals

Literals in Java

A literal is the source code representation of a fixed value.

Literals in Java are a sequence of characters (digits, letters, and other characters) that represent constant values to be stored in variables. Java language specifies five major types of literals. Literals can be any number, text, or other information that represents a value. This means what you type is what you get. We will use literals in addition to variables in Java statement. While writing a source code as a character sequence, we can specify any value as a literal such as an integer.
They are:

  • Integer literals

  • Floating literals

  • Character literals

  • String literals

  • Boolean literals
Each of them has a type associated with it. The type describes how the values behave and how they are stored. 

Integer literals:

Integer data types consist of the following primitive data types: int,long, byte, and short. byte, int, long, and short can be expressed in decimal(base 
10), hexadecimal(base 16) or octal(base 8) number systems as well. 
Prefix 0 is used to indicate octal and prefix 0x indicates hexadecimal when using these number systems for literals.

int decimal = 100;
int octal = 0144;
int hexa =  0x64;

Floating-point literals:

Floating-point numbers are like real numbers in mathematics, for example, 4.13179, -0.000001. Java has two kinds of floating-point numbers: float and double. The default type when you write a floating-point literal is double, but you can designate it explicitly by appending the D (or d) suffix. However, the suffix F (or f) is appended to designate the data type of a floating-point literal as float. We can also specify a floating-point literal in scientific notation using Exponent (short E ore), for instance: the double literal 0.0314E2 is interpreted as:

0.0314 *10² (i.e 3.14).
6.5E+32 (or 6.5E32) Double-precision floating-point literal
7D Double-precision floating-point literal
.01f Floating-point literal

Character literals:

char data type is a single 16-bit Unicode character. We can specify a character literal as a single printable character in a pair of single quote characters such as 'a', '#', and '3'. You must know about the ASCII character set. The ASCII character set includes 128 characters including letters, numerals, punctuation etc. Below table shows a set of these special characters.

 Escape  Meaning
 \n  New line
 \t  Tab
 \b  Backspace
 \r  Carriage return
 \f  Formfeed
 \\  Backslash
 \'  Single quotation mark
 \"  Double quotation mark
 \d  Octal
 \xd  Hexadecimal
 \ud  Unicode character

If we want to specify a single quote, a backslash, or a non-printable character as a character literal use an escape sequence.  An escape sequence uses a special syntax to represents a character. The syntax begins with a single backslash character. You can see the below table to view the character literals use Unicode escape sequence to represent printable and non-printable characters.

 'u0041'  Capital letter A
 '\u0030'  Digit 0
 '\u0022'  Double quote "
 '\u003b'  Punctuation ;
 '\u0020'  Space
 '\u0009'  Horizontal Tab 

String Literals:

The set of characters in represented as String literals in Java. Always use "double quotes" for String literals. There are few methods provided in Java to combine strings, modify strings and to know whether to strings have the same values.

 ""  The empty string
 "\""  A string containing
 "This is a string"  A string containing 16 characters
 "This is a " + "two-line string"  actually a string-valued constant expression, formed from two string literals

Null Literals

The final literal that we can use in Java programming is a Null literal. We specify the Null literal in the source code as 'null'. To reduce the number of references to an object, use null literal. The type of the null literal is always null. We typically assign null literals to object reference variables. For instance
s = null;

Boolean Literals:

The values true and false are treated as literals in Java programming. When we assign a value to a boolean variable, we can only use these two values. Unlike C, we can't presume that the value of 1 is equivalent to true and 0 is equivalent to false in Java. We have to use the values true and false to represent a Boolean value. 

boolean chosen = true;

Remember that the literal true is not represented by the quotation marks around it. The Java compiler will take it as a string of characters, if its in quotation marks.