Lexical Issues

By: aathishankaran Printer Friendly Format    

Lexical Issues

 

Now we will see atomic elements of java. Java programs are a collection of white space identifiers, comments, literals, operators, separators, and keywords. The operators are described in the next article

 

Whitespace

 

            Java is a free-form language. This means that you do not need to follow any special indentation rules. For example, the Example program could have been written all on one line or in any other strange way you felt like typing it, as long as there was at least one whitespace character between each token that was not already delineated by an operator or separator. In java, whitespace is a space, tab, or new line.

 

Identifiers

 

            Identifiers are used for class names, method names, and variable names. An identifier may be any descriptive sequence of uppercase and lowercase letters, numbers or the underscore and dollar sign characters. They must not begin with a number, lest they be confused with a numeric literal. Again, java is case-sensitive, so VALUE is a different identifier the Value.  Some examples of valid identifiers are:

 

AvgTemp            count            a4            $test            this_is_ok

 

Invalid variable names include:

 

2count  high-temp     Not/ok

 

Literals

 

Using a literal representation of it creates a constant value in java. For example, here are some literals:

 

100      98.6            ‘X’            “This is a test”

 

            Left to right, the first literal specifies an integer, the next is a floating-point value, the third is a character constant, and the last is a string. A literal can be used anywhere a value of its type is allowed.

 

Comments

 

            As mentioned, there are three types of comments defined by java. You have already seen two: single-line and multilane. The third type is called a documentation comment. This type of comment is used to produce an HTML file that documents your program. The documentation comment begins with a /** and ends with a*/. Documentation comments are explained in Appendix A.





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