Java - Lexical Issues

Java Programs are collection of white spaces, identifiers, literals, comments, operator, separator and keywords.

White space

White space is a space, tab, new line.

Identifiers

An identifier is the name of class, method and variable.

Identifiers can have uppercase, lowercase letter, numbers, underscore and dollar sign.

They must not begin with a number.

Keyword must not be an identifier, even though keyword can be a part of an identifier.

Example

·       int a

·       class A

·       void sum()

·       (a,sum,A are  identifiers)

Literals

A constant value in java can be known as literal.

Ex: int a=100(100 is a literal)

Literals can be written with underscores.(added in 1.7)

int x=12_34_56;

Comments

There are three types of comments defined by java

·      single line comment //

·      Multiline Comment /* … */

·      Documentation Comment /**……*/

Keywords

·         There are 50 keywords available in java.

·         48 keywords are in use.

·          2 keywords are reserved but not in use. These keywords are goto, const.

·         true, false, null are the values and not keywords.

·         enum keyword is added in J2SE 5

Separator

·        {} - braces

·        [] - brackets

·        () – parentheses

·        . – dot or period

·        , - comma

·        ; - semicolon

Escape Sequences

         \’                 Single quote

         \”                 Double quote

         \\                 Backslash

         \r                 Carriage return

         \n                 Newline

         \f                 Formfeed

         \t                 Tab

         \b                 Backspace