Comments And Data Types in Java

Comments In Java

Whenever we write a program, we should first  think about writing comments.

Comments are description about the features of a program.

There are three types of comments in java 

1. Single line comments
2. Multi line comments
3. Java documentation comments

Single Line Comments

• The single line comment is used to comment only single line.
• These comments start with double slash symbol ' // '.
• After this symbol // , whatever is written till the end of the line is taken as a comment.

Eg:  

       //This is  a one line comment.

Multi Line Comments

•  These comments are used for representing multiple lines.
• Multi line comments start with /* and ends with */.
• In between /* and */ , whatever is written is treated as a comment.

Eg.

      /* This is a multi line comment.

            This is line two of the comment.

            This is line three of the comment.*/

Java Documentation Comments

• These comments start with /** and end with */.
• These comments are used to provide description for every features in a java program.

Eg. 

     /** description about a class*/

         class code

    /*description about a method*/

        method code

Data Types in Java

A variable represents a memory location which holds ' data'.

1. Integer Data Types
2. Float Data Types
3. String Data Types
4. Boolean Data Types

Integer Data Types

These data types represent integer numbers.

Eg.

       int x ;

       x=25;

Here, x is a variable, which can store int(integer) type of data. x is a variable and = represents that the value 25 is stored in to x.This value stored in to x is also called literal.

Float Data Types

These data types are useful to represent numbers with decimal point.

Eg.

       float x = 3.426 ;

Character Data Types

These data type represents a single character like a,b,d,etc,

Eg.

       char ch = 'x' ;

Here, we are storing the single character 'x' in to the variable ch.  x is also called character literal. Whenever the character literals are  written they should be enclosed inside the single quotes.

String Data Types

A string represents a group of characters.

Eg.

      String str = " anu " ;

   Now the string type variable str  contains "anu". Note that any string written directly in a program should be enclosed by using double quotes.

Boolean Data Types

Boolean data type represent any of the two values - true or false.

Eg.

       boolean response = true;

Literals

A literal represents a  value that stored in to a variable directly in the program.

As the data type of the variable changes, the type of literal also changes. so, we have different types of literals.

• Integer literals
• Float literals
• Character literals
• Boolean literals
• String literals

Eg.

       char gender = 'M' ;

        boolean result = false ;

The right hand side values are called literals. Because these values are being stored in to the variable shown at the left hand side.

 Operators In Java 

An operator is a symbol that performs operation. An operator acts on variables called operands.

 Eg;

                  

         a + b   =>  a,b are called operands

                             + is operator

Arithmetic Operator

These operators are used to perform fundamental arithmetic operations like addition, Subtraction,etc.

+    Arithmetic Operator

-      Subtraction Operator

*     Multiplication Operator

/     Division Operator

%    Modulus operator

Unary Operator

As the name indicates, unary operator act on only one operand.

There are three kinds of unary operators :

1. Unary Minus Operator (-)

• This operator is used to negate a given value.
• Negation means converting a negative value in to positive and vise versa.

int x = 3;

System.out.println(-x);  will display -3.

System.out.println(-(x)); will display 3.

   2. Increment Operator (++)

• This operator increases the value of variable by 1.
• Writing ++ before a variable is called pre incrementation.
• Writing  ++ after a variable is called post incrementation.

Eg;

 Finding the difference between pre and post increment of x

Pre incrementation

int x =1;

System.out.println(x);

System.out.println(++x);

System.out.println(x);

Output:

1

2

2

Post incrementation

int x = 1;

System.out.println(x);

System.out.println(x++);

System.out.println(x);

output:

1

1

2

 3. Decrement operator (--)

• This operator is used to decrement the values of a variable by 1.
• Writing -- before a variable is called pre decrementation.
• Writing -- after a variable is called post decrementation.

Eg.

       int x = 1;

       --x  will make the value of x as 0

       x-- will make the value of x as -1

              

Assignment Operator(=)

• This operator is used to store some values in to a variable.
• It is used in 3 ways:

1. It is used to store a value in to a variable.

          Eg. int x = 7 ;

     

     2. It is used to store value of  a variable in to another variable.

        

           Eg. int x = y ;

     

     3. It is used to store value of an expression in to a variable.

         Eg. int x = y+z-2 ;

Relational Operator

These operators are used  for the purpose of comparing. Relational operators are of 6 types.

• > greater than
• < less than
• >= greater than or equal to
• <= less than or equal to
• == equal to operator
• != not equal to operator

Logical Operators

Logical operators are used to construct compound conditions. A compound condition is a combination of several simple conditions. Logical operators are of three types.

1. || or operator
2. && and operator
3. ! not operator

Eg.

  

      if(a == 1 || b = = 1 || c ==1) System.out.println("yes");

Here, there are three conditions a==1  b==1 and c==1 which are combined by || (or operator). In this case, if either of the a or b or c value becomes equal to 1 , "yes "will be displayed.

Click on the link below to know about

Statements In Java

Anu K Joy